Geography

1VENKAT RAMAN REDROWTU

CONCEPTS OF GEOGRAPHY

UNIVERSE & ORIGIN

The origin of the Universe is unknown — it is theultimate mystery of this whole story OF UNIVERSE. Thelaws of physics which applied in the beginning are notclear, so it is hard to guess where it might have come from.There are several theories of how the Universe began. Butthe one most acceptable and plausible is BIGBANGTHEORY. The Universe is what we can see from Earth -sometimes called the observable Universe. The Universe isjust a tiny part of the Cosmos. It is because the Cosmosinflated that the Universe seems flat. Space in theMacrocosms might have been curved, so that, for example,the angles in a triangle did not add up to 180 degrees. Butas the tiny region, which would eventually become theUniverse was expanded, this curvature was almost entirelyflattened out, in the same way as the curvature of thesurface of a soccer ball would be flattened out if you blewit up to the size of the Earth. We use the wordMacrocosm0s to mean “everything there is”. We will seethat the Cosmos and the Universe are just small parts ofthe Macrocosmos. cosmic inflation removes vast parts ofthe total universe from our observable horizon, mostcosmologists accept that it is impossible to observe thewhole continuum and may use the expression our universe,referring to only that which is knowable by human beingsin particular. In cosmological terms, the universe is thoughtto be a finite or infinite space-time continuum in which allmatter and energy exist. Some scientists hypothesize thatthe universe may be part of a system of many otheruniverses, known as the multiverse.

MULTIVERSE

There is some speculation thatmultiple universes exist in a higher-levelmultiverse (also known as a megaverse),our universe being one of thoseuniverses. For example, matter that fallsinto a black hole in our universe could emerge as a BigBang, starting another universe. However, all such ideasare currently untestable and cannot be regarded as anythingmore than speculation..

BIG BANG THEORY:

It explains how everything we see today was createdby a single point of matter.The Big Bang was thebeginning of space and time, as many physicists believetoday. Note that this is only a theory and has not yetbeen proven, but several key observations have been

made that support it. In the beginning of our time frame,all of the matter that exists today in the universe waspacked into a single point inspace-time, known as asingularity.

A singularity is a point thathas infinite density and is infinitelysmall. At one moment, all of thismatter exploded outward in whatis called a Big Bang. This matterhas been expanding and forming different structures likegalaxies and other celestial bodies ever since. Dependingon the average density of matter and energy in the universe,it will either keep on expanding forever or it will begravitationally slowed down and will eventually collapse backon itself in a “Big Crunch”. Currently the evidencesuggests not only that there is insufficient mass/energy tocause a recollapse, but that the expansion of the universeseems to be accelerating and willaccelerate for eternity.Up untilthe 1920s, it was believed thatUNIVERSE was static andeverlasting. But until EdwinHubble came along. In 1929,Edwin Hubble made amonumental observation thatchanged the course of astronomy.He discovered that galaxies far away from us have a redshift. This means that they are moving away from us andthus, must have been closer together at some point; andso, ultimately they must have existed in one point in space,a singularity. According to the Big Bang, the universeemerged from an extremely dense and hot state (bottom).Since then, space itself has expanded with the passage oftime, carrying the galaxies with it. A fundamental aspectof the Big Bang can be seen today in the observation thatthe farther away from us galaxies are, the faster they moveaway from us. The Big Bang is the scientific theory thatthe universe emerged from a tremendously dense and hotstate about 13.7 billion years ago. The theory is based onthe observations indicating the expansion of space (inaccord with the Robertson-Walker model of generalrelativity) as indicated by the Hubble redshift theory,which can be explained by DOPPLER’S EFFECT.

Hubble’s law is the statement in physical cosmologythat the redshift in light coming from distant galaxies isproportional to their distance. The law was first formulatedby Edwin Hubble and Milton Humason.

How the pioneers of cosmology found theinformation necessary to prove the Big Bang with only atelescope and a spectrograph?

DOPPLER’S EFFECT proves the expansion ofthe universe. The Doppler effect, named after ChristianAndreas Doppler, is the apparent change in frequencyand wavelength of a wave that is perceived by an observermoving relative to the source of the waves. The Dopplereffect produces different types of shift in respect to thewaves and their frequency. The shorter the wavelength oflight, the more blue shifted it is, and the longer thewavelength, the more red shifted it is. These shifts are usedby modern-day cosmologists to determine whether an objectin space is heading towards or away from us. Many of theobjects seen in the night sky, the average stars, nebulasand galaxies, emit light that becomes red shifted as it fliestowards us. This was first seen by Edwin Hubble in the1920s. At the time, the popular theory of the universe wasthat it was a static entity. However, this newfound fact,that many objects were heading away from us, seen in alldirections, pointed to one theory, that the universe wasexpanding. It was also found that the farther one delvesinto the midst of space, the quicker the objects are recedingfrom us.• Cosmology The astrophysical study of the history,

structure, and dynamics of the universe.• Astronomy the scientific study of matter in outer

space, especially the positions, dimensions, distribution,motion, composition, energy, and evolution of celestialbodies and phenomena

• Astrophysics The part of astronomy that dealsprincipally with the physics of the universe, includingluminosity, density, temperature, and the chemicalcomposition of stars, galaxies, and the interstellar

• Big Bang is the theory of cosmology in which theexpansion of the universe is presumed to have begunwith a primeval explosion (referred to as the “BigBang”).

• Ptolemy (ca.100-ca.170): Ptolemy believed the planetsand Sun to orbit the Earth in the order Mercury,Venus, Sun, Mars, Jupiter, and Saturn. This systembecame known as the Ptolemaic system

• Nicolas Copernicus, (1473-1543) Polish astronomerwho advanced the theory that the Earth and otherplanets revolve around the Sun (the “heliocentric”theory). This was highly controversial at the time, sincethe prevailing Ptolemaic model held that the Earthwas the center of the universe, and all objects,including the sun, circle it. The Ptolemaic model hadbeen widely accepted in Europe for 1000 years whenCopernicus proposed his model. (It should be noted,however, that the heliocentric idea was first put forthby Aristarcus of Samos in the 3rd century B.C., afact known to Copernicus but long ignored by othersprior to him).

• EUD: Exploration of the Universe Division, located

at NASA’s Goddard Space Flight Center. The scientists,programmers and technicians working here study theastrophysics of objects which emit cosmic ray, x-rayand gamma-ray radiation.

• Galaxy: A component of our universe made up ofgas and a large number (usually more than a million)of stars held together by gravity.

• GalileoGalilei,(1564-1642):An Italian scientist, Galileowas renowned for his epoch making contribution tophysics, astronomy, and scientific philosophy. He isregarded as the chief founder of modern science. Hedeveloped the telescope, with which he found craterson the Moon and discovered the largest moons ofJupiter. Galileo was condemned by the CatholicChurch for his view of the cosmos based on thetheory of Copernicus.

• Edwin Hubble,(1889-1953):American astronomerwhose observations proved that galaxies are “islanduniverses”, not nebulae inside our own galaxy. Hisgreatest discovery, called “Hubble’s Law”, was thelinear relationship between a galaxy’s distance and thespeed with which it is moving. The Hubble SpaceTelescope is named in his honor.

• Nebula (pl.nebulae): A diffuse mass of interstellardust and gas

• Implosion: A violent inward collapse. An inwardexplosion

• WMAP (Wilkinson Microwave Anisotropy Probe)A NASA satellite designed to detect fluctuations inthe cosmic microwave background. From its initialresults published in Feb 2003, astronomers pinpointedthe age of the universe, its geometry, and when thefirst stars appeared.

TIMELINE OF COSMOLOGY:

The timeline of cosmology lists the sequence ofcosmological theories and discoveries in chronological order.The most modern developments follow the scientificdevelopment of the discipline of physical cosmology.

c500 onwards - Several astronomers propose a Sun-centered Universe, including Aryabhata, Bhaskara I,Ibn al-Shatir, and Copernicus

2nd century - Ptolemy proposes an Earth-centredUniverse, with the Sun and planets revolving aroundthe Earth

1687 - Sir Isaac Newton’s laws describe large-scalemotion throughout the universe

1791 - Erasmus Darwin pens the first description ofa cyclical expanding and contracting universe

1905 - Albert Einstein publishes the Special Theoryof Relativity, positing that space and time are notseparate continuums

1915 - Albert Einstein publishes the General Theoryof Relativity, showing that an energy density warps

spacetime

1922 - Alexander Friedmann finds a solution to theEinstein field equations which suggests a generalexpansion of space

1929 - Edwin Hubble demonstrates the linear redshift-distance relation and thus shows the expansion of theuniverse

1948 - Ralph Alpher, Hans Bethe(“in absentia”), andGeorge Gamow examine element synthesis in a rapidlyexpanding and cooling universe and suggest that theelements were produced by rapid neutron capture

1948 - Hermann Bondi, Thomas Gold, and FredHoyle propose steady state cosmologies based on theperfect cosmological principle

1950 - Fred Hoyle derisively coins the term “BigBang”.

1963 - Fred Hoyle and Jayant Narlikar show that thesteady state theory can explain the isotropy of theuniverse because deviations from isotropy andhomogeneity decay exponentially in time

1965 - Arno Penzias and Robert Wilson, astronomersat Bell Labs discover the 2.7 K microwave backgroundradiation, which earns them the 1978 Nobel Prize inPhysics. Robert Dicke, James Peebles, Peter Roll andDavid Todd Wilkinson interpret it as relic from thebig bang.

1966 - Stephen Hawking and George Ellis show thatany plausible general relativistic cosmology is singular

1967 - Andrei Sakharov presents the requirements forbaryogenesis, a baryon-antibaryon asymmetry in theuniverse

1990 - Preliminary results from NASA’s COBE missionconfirm the cosmic microwave background radiationis an isotropic blackbody to an astonishing one partin 105 precision, thus eliminating the possibility of anintegrated starlight model proposed for the backgroundby steady state enthusiasts.

1998 - Adam Riess, Saul Perlmutter and others discoverthe cosmic acceleration in observations of Type Iasupernovae providing the first evidence for a non-zerocosmological constant. This is confirmed bymeasurements of the cosmic microwave backgroundradiation by the BOOMERanG experime

2003 - NASA’s WMAP takes more detailed picturesof the cosmic microwave background radiation thanwere obtained by the BOOMERanG experiment. Theimage can be interpreted to indicate that the universeis 13.7 billion years old (within one percent error) andconfirm that the Lambda-CDM model and theinflationary theory are correct.

2006 - The long-awaited three-year WMAP results are

released, confirming previous analysis, correctingseveral points, and including polarization data

SNIPPETS• HUBBLE’S LAW is considered the first

observational basis for the expanding spaceparadigm and today serves as one of the most oftencited pieces of evidence in support of the Big Bang

• The observed expansion of the universe (Hubble’s law)began — calculated to be 13.7 billion (1.37 × 1010)years ago (±2%).

• The composition of primordial matter throughnucleosynthesis( as explained by BIG BANG) waspredicted by the Alpher-Bethe-Gamow theory.

• NASA’s Wilkinson Microwave Anisotropy Probe(WMAP) project estimates the age of the universe tobe: (13.7 ± 0.2) × 109 years.

• Dark matter : Dark matter is matter that does notemit or reflect enough electromagnetic radiation (such aslight, X-rays and so on) to be detected directly, butwhose presence may be inferred from its gravitationaleffects on visible matter.

• The composition of dark matter is unknown, but mayinclude new elementary particles such as WIMPs andaxions, ordinary and heavy neutrinos, dwarf stars andplanets collectively called MACHOs, and clouds ofnonluminous gas.

CELESTIAL BODIES

GALAXIES: Galaxies are MAGNANIMOUSsystems of stars and interstellar matter. Galaxies arelocated in the billions all throughout the universe andcontain many MILLIONS of stars; these numbers rangefrom the millions to the trillions. A typical galaxy is100,000 light-years in diameter. There are four differenttypes of galaxies the universe contains—or the only fourtypes that have been discovered: spiral, irregular,lenticular and elliptical.

Spiral galaxies, like *our own Milky Way, have twomain parts to them: the main, flat disk in the center, withthe younger generations of stars arranged in a spiral patternemerging from the central disk. Our galaxy, the Milky Way,has several of these arms spiraling outward from the centraldisk: arms such as the Orion Arm, in which we are located,the Sagittarius Arm and more.

Lenticular galaxies in effect spiral galaxies withoutany arms emerging from the center. They appear to besimply flat disks in the sky. The reason why these galaxieshave not become spiral is because all of the interstellarmatter they had in the beginning was used up. Therefore,Lenticular Galaxies are mostly if not fully composed ofthe older generations of stars.

Elliptical Galaxies usually appear to be eitherstrangely circular or highly eccentric in shape. The galaxiesoften seem to be just large masses of stars without a

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CONCEPTS OF GEOGRAPHYcommon center because the stars in these types ofgalaxies do not rotate together as a group. EllipticalGalaxies, as Lenticular ones, have little interstellarmatter to create new stars with and are, again,composed of mostly older generation stars.

Irregular Galaxies, as their name suggests, have noparticular shapes as the spiral or Lenticular Galaxies do.This is due to the many neighboring celestial objects thatexert a gravitational pull on these galaxies making themirregular. Some galaxies float through space by themselvesand are lonely wanderers. But many galaxies occur in largegroups in which they create large gravitational fields thatalter the galaxies’ appearances. The numbers of galaxies ina cluster could range from a few to a dozen to severalthousand.• Our Milky Way galaxy: The Milky Way (a translation

of the Latin Via Lactea, in turn derived from theGreek Galaxia Kuklos) is the galaxy in which the Earthis found. When viewed from the Earth and itsenvirons, it appears in the night sky as a hazy bandof white light (hence “milky”) across the celestialsphere, formed by stars within the disc of its namesakegalaxy. It is also simply known as the Galaxy, as theEarth’s solar system is a part of it. The Milky Wayappears brightest in the direction of Sagittarius, wherethe galactic center lies. Our galaxy is a part of clusterof 13 other galaxies called LOCAL GROUP.

• Andromeda Galaxy: The Andromeda Galaxy (alsoknown as Messier Object 31, M31, or NGC 224; oldertexts often call it the Andromeda Nebula) is a giantspiral galaxy in the Local Group, together with theMilky Way galaxy. It is at a distance of approximately2.9 million light years or 900 kpc, in the direction ofthe constellation Andromeda.With a mass of about1.5 times more than the Milky Way, it is the dominantgalaxy of the Local Group, which consists of about30 small galaxies plus three large spirals: Andromeda,Milky Way and M33.

• The two nearest galaxies to our home galaxy areLARGE MAGELLANIC CLOUD and SMALLMAGELLANIC CLOUD.

• A system of galaxies containing from a few to a fewthousand-member galaxies which are all gravitationallybound to each other are called cluster of galaxies.

• Cluster of galaxies typically organized in to distinctshapes are called constellations and are namedaccording to such shapes and geometric figures. Thereare 88 constellations identified so far. HYDRA is thelargest, crux is the smallest constellation. Thebrightest stars within a constellation is named fromthe name of the constellation it self, using Greekalphabet and Latin genitive form for the constellation.For Example alphe urse majoris is the brighteststar in Ursa Major constellation.

ASTERIODS: An asteroid is a small, solid object in our

Solar System, orbiting the Sun. An asteroid is anexample of a minor planet (or planetoid). Theseminor planets are much smaller than the smallplanets such as Mercury or Mars. It is believedthat most asteroids are remnants of theprotoplanetary disc. The incorporation of theseremnants into the planets during the formation ofthe Solar System was prevented by largegravitational perturbations induced by Jupiter.Some asteroids have moons. The vast majority ofthe asteroids are within the main asteroid belt, withelliptical orbits between those of Mars and Jupiter.There are two OTHER main groups of asteroidsin our solar system.One of these groups is called the Near Earth

Asteroids :These rocks, while orbiting the sun, often are in close

proximity to the Earth and there have been some fearsthat possible collisions may occur, but so far nothing onany great scale has taken place in the past decade or so.So these asteroids rarely cause any disturbances or worryamong people and the likelihood for an asteroid to impactthe earth is very small. The other group is called the TrojanAsteroids. These pieces of rock and debris orbit Jupiterand are usually either a little ahead or a little behind theplanet in its orbit.• Johann Bode popularized a relationship giving

planetary distances from the Sun, which becameknown as “Bode’s law”; predicted an undiscoveredplanet between Mars and Jupiter, where the asteroidswere later found

• In the last years of the 18th century, Baron FranzXaver von Zach organized a group of 24 astronomersto search the sky for the “missing planet” predictedat about 2.8 AU from the Sun by the Titius-Bodelaw, partly as a consequence of the discovery, by SirWilliam Herschel in 1781, of the planet Uranus atthe distance “predicted” by the law.

• The first asteroid, Ceres, was not discovered by amember of the group, but rather by accident in 1801by Giuseppe Piazzi director, at the time, of theobservatory of Palermo, in Sicily. Piazzi named it afterCeres, the Roman goddess of agriculture

• Three other asteroids (Pallas, Juno, Vesta) werediscovered over the next few years.

• The three most important groups of near-Earthasteroids are the Apollos, Amors, and the Atens.

• NASA is planning to launch the Dawn Mission in2007, which will orbit both Ceres and Vesta in 2011-2015.It has been suggested that asteroids might beused in the future as a source of materials which maybe rare or exhausted on earth (asteroid mining).

NEBULA :Nebulas are magnificently beautiful celestial clouds

composed mostly of hydrogen gas and interstellar dust


CONCEPTS OF GEOGRAPHYparticles. Many nebulas throughout the universe existin galaxies. There are many types of nebulas; morespecifically, four main types. The categories arePlanetary, Diffuse, Supernova Remnants and DarkNebulas. There are also nebulas under the categoryHerbig-Haro. These types are very bright and small.This effect is due to jets of gas and other particles, whichare expelled by a star during its stages of formation.Planetary Nebulas, as their name suggests, resembleplanets. In actuality, however, these nebulas are theshells of star material a red giant sheds during its deathstages (when it transforms into a white dwarf star). Sincethese red giants shedlayers, or clouds of gasand other material, thisgoes along with thedefinition of a nebula.

COMETS :

A comet isbasically a ball of iceand dust that looks likea star with a tail. Somecomets do not havetails, looking like hazy,round spots of light.Comets are believed tooriginate in a cloud (the Oort cloud) at large distancesfrom the sun consisting of debris left over from thecondensation of the solar nebula; the outer edges ofsuch nebulae are cool enough that water exists in asolid (rather than gaseous) state. Asteroids originate viaa different process, but very old comets which havelost all their volatile materials may come to resembleasteroids. Most comets have three parts: a nucleus, ahead (coma), and a tail. The comets in our solar systemusually have very long orbits and spend most of thistime away from the sun. During these periods, cometsappear to be just simple heaps of rock, dust and icetraveling through the cosmos. But when a comet istraveling towards and near the sun, it has several clearparts: the nucleus, coma, hydrogen cloud, dust tail andion tail. Many comets in our solar system often havehuge orbits; some even exceed the orbit of Pluto. Today,most comets are located outside our solar system inpart of the original cloud of dust and gas that hasremained virtually untouched for billions of years. Theseregions are referred to as the Oort cloud and the KuiperBelt. The total number of comets within this belt wasestimated as a trillion.

• The Oort Cloud was first theorized by the Dutchastronomer Jan Oort in 1950.

• The Kuiper Belt is a region first theorized by theDutch-American astronomer Gerard Kuiper in 1951.Kuiper conjectured that a belt of comets probablyexisted outside the orbit of Neptune within the rangeof 30 to 50 astronomical units (2.8 to 4.6 billion miles)

from the sun

• Collisions and perturbations by the planets of oursolar system are believed to be the reasons for theejection of bodies from this belt.

• Comet Halley or Halley’s Comet (its officialdesignation is 1P/Halley). Its next appearance is duein 2061.

• The second comet to be discovered to have a periodicorbit was Comet Encke.

METEORS AND METEORITES

A meteor is the visible path of a meteoroid thatenters the Earth’s (or another body’s) atmosphere,commonly called a shooting star or falling star. It isprobably a piece of remnant piece of comets, whichare scattered in interplanetary spaces. They give off astreak of bright light when it burns up in Earth’satmosphereMeteorite:

A meteorite is an extraterrestrial body that survivesits impact with the Earth’s atmosphere without beingdestroyed. While in space it is called a meteoroid. Whenit enters the atmosphere, air resistance causes the body toheat up and emit light, thus forming a fireball, also knownas a meteor or shooting star.• A very bright meteor may be called a fireball or

bolide. The International Meteor Organizationdefines fireballs as being meteors of magnitude -3or brighter.

• A meteor striking the Earth or other object is calledMeteorite and may produce an impact called crater.Ex Baringer crater near flag staff

• Molten terrestrial material “splashed” from such acrater can cool and solidify into an object known as atektite.

• The only known examples of meteorites that didn’tfall on Earth are Heat Shield Rock, which was foundon Mars, and two tiny fragments of asteroids that werefound among the samples collected on the Moon byApollo 12 (1969) and Apollo 15 (1971) astronauts.

• Meteor shower can be seen when Earth passesthrough a trail of dust left by any comet ininterplanetary spaces.

• Leonid Shower was a meteor shower, whichoriginated in the constellation LEO and actuallycaused by the dust of comet Temple turtle.

THE STARRY WORLD

STARS : Scientifically, stars are defined as self-gravitating spheres of plasma in hydrostatic equilibrium,which generate their own energy through the process ofnuclear fusion. Stars are not spread uniformly across theuniverse, but are typically grouped into galaxies. A typicalgalaxy contains hundreds of billions of stars. The energy

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CONCEPTS OF GEOGRAPHYproduced by stars radiates into space as electromagneticradiation, as a stream of neutrinos* from the star’s core,and as a stream of particles from the star’s outer layers(its stellar wind). The peak frequency of the light dependson the temperature of the outer layers of the star.Besides the emitted visible light, the ultraviolet andinfrared components are typically far from negligible.The apparent brightness of a star is measured by itsapparent magnitude. Stellar astronomy is the study ofstars and the phenomena exhibited by the variousforms/developmental stages of stars There are manytypes of stars ranging from the very small and dense, tothe very large and hot. All have different properties aswell and are categorized into four main groups: Dwarfs,Giants, Binary stars and Neutron stars.

* Neutrino: A fundamental particle produced inmassive numbers by the nuclear reactions in stars.

Dwarf stars are classified in four groups: red,yellow, white and brown dwarfs. Red dwarfs are small,somewhat cool stars; yellow dwarfs are relatively small andnot very hot, like our sun. These stars are very commonthroughout our universe. White dwarfs are small, very hotand very dense stars; their sizes are close to that of Earth.White dwarfs are mainly composed of carbon and are theremnants of a Red Giant that has lost its outer layersduring the final stages of its life. Brown dwarfs are starsthat do not have enough mass to continue nuclear fusionwithin the core.

Giant stars: There are three main categories of giants:red, blue and super-giants. A Red giant is a star thathas expanded from its original size in the last stages of itslife. If they become cooler and are usually orange in color.Blue giants are also very large and very massive, but unlikered giants, they are very hot as well. Super-giants areextremely large stars, sometimes the size of our solarsystem. These stars are rare in the universe and they die inthe form of a cataclysmic explosion called a supernovaand result in the formation of a black hole.

Neutron stars form in the aftermath of a supernovaexplosion. They are extremely dense and very small, about5-16 kilometers in diameter. The reason why they do notbecome black holes is because the star they formed fromwas not massive enough to create such an effect. Pulsarsare also neutron stars, only they spin very rapidly andemit short but strong bursts of energy. If one noticesa pulsar in the night sky, it will look like an ordinary starthat is simply flashing.

A Binary star system is one that contains two starsorbiting around a common center of mass larger thantheirs. An eclipsing binary system is one that contains alarge star and a smaller star orbiting it. This type of systemproduces either a brightening or occluding effect, dependingon whether the smaller star enhances the larger star’sbrightness or occludes it; this depends on the position ofthe smaller star in its orbit.

An X-Ray binary system is made up of a normal,living star and a collapsed star, which could be a whitedwarf, a black hole or a neutron star. If these two starsare close enough to each other, the collapsed star will beginto suck material away from the normal one. As thematter is sucked into the white dwarf, black hole orneutron star, an immense amount of heat is produced,which results in the emissions of x-rays.

Pulsar: A rotating Neutron star, which generatesregular pulses of radiation. Pulsars were discovered byobservations at radio wavelengths but have since beenobserved at optical, X-ray, and gamma-ray energies.

Nova (plural: novae): A star that experiences asudden outburst of radiant energy, temporarily increasingits luminosity by hundreds to thousands of times beforefading back to its original luminosity

SUPERNOVA (PLURAL : SUPERNOVAE)(a) The death explosion of a massive star, resulting in a

sharp increase in brightness followed by a gradualfading. At peak light output, these types of supernovaexplosions (called Type II supernovae) can outshinea galaxy. The outer layers of the exploding star areblasted out in a radioactive cloud. This expandingcloud, visible long after the initial explosion fades fromview, forms a supernova remnant (SNR).

(b) The explosion of a white dwarf, which hasaccumulated enough material from a companion starto achieve a mass equal to the *Chandrasekhar limit.These types of supernovae (called Type Ia) haveapproximately the same intrinsic brightness, and canbe used to determine distances.

• Chandrasekhar limit A limit, which mandates that no whitedwarf (a collapsed, degenerate star) can be more massive thanabout 1.4 solar masses. Any degenerate object more massivemust inevitably collapse into a neutron star

Black hole: Black hole formation owes some thingto supernova. A black hole is the result of the collapseof a very massive star. A supernova, however, does notalways lead to the formation of a black hole. White dwarfsand neutron stars are the products of these explosions aswell. A black hole is only created when the star isextremely massive and large called super giants. Undernormal conditions, a star will burn hydrogen fuel,converting it into helium. During the last stages of thestar’s life, when the hydrogen fuel runs out, the star beginsto burn helium into a heavier element. These elements thatare burned, other than hydrogen, create an imbalancebetween the gravitational forces and the nuclear forces thatunder normal conditions keep the star stable. Due to thisimbalance, gravity takes over and the star begins to collapseupon itself until it reaches a point of infinite density andinfinitely small size, in other words, a singularity. Thissingularity, now known as a black hole, creates a massivegravitational effect unlike any other. This effect is so great,that even light cannot escape its gravitational pull.


CONCEPTS OF GEOGRAPHYA black hole also has an event horizon, the

boundary of the black hole from where anything canbe pulled in with enormous gravitational pull.

QUASARS are enormously bright object at the edgeof our universe, which emits massive amounts of energy.In an optical telescope, they appear point-like, similar tostars, from which they derive their name (quasar =quasi-stellar). Quasars are thought to be the most distantobjects yet discovered by mankind. The name quasar isshort for the term: ‘quasi stellar radio source.’ Thereason why this celestial body has this full name isbecause the method at first used to discover these objectsinvolved a relationship between radio-sources andoptical-sources. Astronomers have discovered thatQuasars are enormously red shifted. What this meansis that as the universe is expanding, the light waves froma Quasar are being stretched. The more the red shift,the farther they are away. Hence, the farther they areaway, the longer it takes for its light to reach us. SoQuasars basically give scientists a view of the early,primordial universe. Quasars produce enormous amountsof energy. These values can be as much as 100 galaxiescombined. Quasars also can be as bright as a trillion ofour suns. In other words, in one second, a Quasar producesenough power to satisfy the electrical needs of earth forthe next billion years. The reason for this amazing powerand illumination is because in the center of a Quasar theremay be a super-massive black hole with many starssurrounding it. Current theories hold that quasars are onetype of AGN.

Active Galactic Nuclei (AGN)

A class of galaxies, which spew massive amounts ofenergy from their centers, far more than ordinary galaxies.Many astronomers believe super massive black holes maylie at the center of these galaxies and power their explosiveenergy output.

Quasi-Stellar Source (QSS)

Sometimes also called quasi-stellar object (QSO); Astellar-appearing object of very large red shift that is astrong source of radio waves; presumed to be extragalacticand highly luminous.• A star generates energy through nuclear fusion and

therefore emits light.• All stars except the Sun appear as shining points in

the nighttime sky that twinkle because of the effectof the Earth’s atmosphere and their distance from us.

• The nearest star to the Earth, apart from the Sun, isProxima Centauri, which is 39.9 trillion kilometers,or 4.2 light years away (light from Proxima Centauritakes 4.2 years to reach Earth).

• Astronomers estimate that there are at least 70sextillion (70×1021) stars in the known universe. Thatis 70 000 000 000 000 000 000 000, or 230 billiontimes as much as the 300 billion in our own Milky

Way.• The smallest known star undergoing fusion in its

core is AB Doradus C, a companion to ABDoradus A, which has a mass only 93 times thatof Jupiter.

• High mass stars powerfully illuminate the cloudsfrom which they formed. One example of such anebula is the Orion Nebula.

• A black dwarf constitutes the remains of a Sun-sized star, which has evolved to a white dwarf andsubsequently cooled down such that it only emits blackbody radiation. The sun: The Sun is the closest star to Earth. The

strong gravitational pull of the Sun holds Earth and theother planets in the solar system in orbit. The Sun’s lightand heat influence all of the objects in the solar systemand allow life to exist on Earth. The Sun is an averagestar its size, age, and temperature fall in about the middleof the ranges of these properties for all stars. Astronomersbelieve that the Sun is about 4.6 billion years old and willkeep shining for about another 7 billion years.Mean distance fromEarth : 149.6×106 km(92.95×106

mi)(8.31 minutes at the speedof light)

Visual brightness (V) : “26.8m

Absolute magnitude : 4.8m

Spectral classification : G2VOrbital characteristicsMean distance from theMilky Way core : ~2.5×1017 km(26,000-28,000

light-years)Galactic period : 2.25-2.50×108 aVelocity : 217 km/s orbit around the

center of the Galaxy, 20 km/srelative to average velocity ofother stars in stellarneighborhood

Physical characteristicsMean diameter : 1.392×106 km(109 Earth

diameters)Circumference : 4.373×106 km(342 Earth

diameters)Oblation : 9×10"6

Surface area : 6.09×1012 km²(11,900 Earths)Volume : 1.41×10 18 km³(1,300,000

Earths)Mass : 1.988 435×1030 kg(332,946

Earths)Density : 1.408 g/cm³Surface gravity : 273.95 m s-2(27.9 g)

IN SIDE THE SUNCore :

The core of the Sun is considered to extend fromthe center to about 0.2 solar radii. It has a density of up

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CONCEPTS OF GEOGRAPHYto 150,000 kg/m3 (150 times the density of water onEarth) and a temperature of close to 13,600,000 Kelvins(by contrast, the surface of the Sun is close to 5,785Kelvins (1/2350th of the core)). Through most of theSun’s life energy is produced by nuclear fusion througha series of steps called the p-p (proton-proton) chain; thisprocess converts hydrogen into helium. The core is the onlylocation in the Sun that produces an appreciable amountof heat via fusion: the rest of the star is heated by energythat is transferred outward from the core. All of theenergy produced byfusion in the core musttravel through manysuccessive layers to thesolar photospherebefore it escapes intospace as sunlight orkinetic energy ofparticles.

Radiation zone :

From about 0.2 to about 0.7 solar radii, solarmaterial is hot and dense enough that thermal radiationis sufficient to transfer the intense heat of the coreoutward.Escape velocity fromthe Surface : 617.54 km/s (55 Earths)Surface temperature : 5785 KTemperature of corona : 5 MKCore temperature : ~13.6 MKLuminosity (Lsol) : 3.827×1026 W~3.75×1028 lm

(~98 lm/W efficacy)

STRUCTURE OF THE SUN

Convection zone :

From about 0.7 solar radii to the Sun’s visible surface,the material in the Sun is not dense enough or hot enoughto transfer the heat energy of the interior outward viaradiation. As a result, thermal convection occurs as thermalcolumns carry hot material to the surface (photosphere)of the Sun. Once the material cools off at the surface, itplunges back downward to the base of the convection zone,to receive more heat from the top of the radiative zone.Convective overshoot is thought to occur at the base ofthe convection zone, carrying turbulent downflows into theouter layers of the radiative zone.

Photosphere :

The visible surface of the Sun, the photosphere, isthe layer below which the Sun becomes opaque to visiblelight. Above the photosphere visible sunlight is free topropagate into space, and its energy escapes the Sun entirely.The change in opacity is because of the decreasing overallparticle density: the photosphere is actually tens to hundredsof kilometers thick.

Atmosphere :

During a total solar eclipse, the sun’s atmosphere ismore apparent to the eye.The parts of the Sun abovethe photosphere are referred to collectively as the solaratmosphere. They can be viewed with telescopes operatingacross the electromagnetic spectrum, from radio through visiblelight to gamma rays, and comprise five principal zones:

The Chromosphere, the Transition region, theCorona, and the Heliosphere.

The Heliosphere, which may be considered thetenuous outer atmosphere of the Sun, extends outward pastthe orbit of Pluto to the heliopause, where it forms a sharpshock front boundary with the interstellar medium. TheChromosphere, the Transition region, and Corona aremuch hotter than the surface of the Sun; the reason whyis not yet known.

The Chromosphere : The coolest layer of the Sunis a temperature minimum region about 500 km above thephotosphere, with a temperature of about 4,000 K.Abovethe temperature minimum layer is a thin layer about2,000 km thick, dominated by a spectrum of emission andabsorption lines. It is called the chromosphere from the Greekroot chroma, meaning color, because the chromosphereis visible as a colored flash at the beginning and end oftotal eclipses of the Sun. The temperature in thechromosphere increases gradually with altitude, ranging upto around 100,000 K near the top.

Transition region :Above the chromosphere is atransition region in which the temperature rises rapidly fromaround 100,000 K to coronal temperatures closer to onemillion K. The increase is because of a phase transition ashelium within the region becomes fully ionized by the hightemperatures.

The corona:It is the extended outer atmosphere ofthe Sun, which is much larger in volume than the Sun itself.The corona merges smoothly with the solar wind that fillsthe solar system and heliosphere. The dark linesin the coronaare called FRAUNHOFER LINES.

The heliosphere:It extends from approximately 20solar radii (0.1 AU) to the outer fringes of the solar system.

SOLAR ACTIVITY :

Sunspots : When observing the Sun with appropriatefiltration, the most immediately visible features are usuallyits sunspots, which are well-defined surface areas thatappear darker than their surroundings because of lowertemperatures. Sunspots are regions of intense magneticactivity where convection is inhibited by strong magneticfields, reducing energy transport from the hot interior tothe surface.

Solar cycle : The number of sunspots visible on theSun is not constant, but varies over a 10-12 year cycleknown as the Solar cycle. The solar cycle has a greatinfluence on space weather, and seems also to have a stronginfluence on the Earth’s climate. Solar minima tend to be


CONCEPTS OF GEOGRAPHYcorrelated with colder temperatures, and longer thanaverage solar cycles tend to be correlated with hottertemperatures. In the 17th century, the solar cycle appearsto have stopped entirely for several decades; very fewsunspots were observed during this period. During thisera, which is known as the Maunder minimum or LittleIce Age, Europe experienced very cold temperatures.

Solar flare : It is a violent explosion in the Sun’satmosphere with an energy equivalent to a billion megatonnuclear bombs, traveling at about 1 million km per hour.Solar flares take place in the solar corona and chromosphere,heating plasma to tens of millions of kelvins andaccelerating the resulting electrons, protons and heavier ionsto near the speed of light. They produce electromagneticradiation across the electromagnetic spectrum at allwavelengths from long-wave radio to the shortest wavelengthGamma rays. Most flares occur around sunspots, whereintense magnetic fields emerge from the Sun’s surface intothe corona.

A solar wind is a stream of charged particles (i.e., aplasma) which are ejected from the upper atmosphere ofa star. When originating from stars other than the Earth’sSun, it is sometimes called a stellar wind.It consists mostlyof high-energy electrons and protons (about 1 keV) thatare able to escape the star’s gravity in part because of thehigh temperature of the corona and the high kinetic energyparticles gain through a process that is not well understoodat this time. Many phenomena are directly related to thesolar wind, including: geomagnetic storms that can knockout power grids on Earth, auroras, why the tail of a cometalways points away from the Sun, and the formation ofdistant stars.

solar constant is the amount of incoming solarradiation per unit area, measured on the outer surface ofEarth’s atmosphere, in a plane perpendicular to the rays. Itis measured by satellite to be roughly 1366 watts per squaremetre.Thus, for the whole Earth, with a cross section of127,400,000 km², the power is 1.740×1017 W. The solarconstant is not quite constant

VAN ALLEN RADIATION BELT

Solar activity has several effects on the Earth and itssurroundings. Because the Earth has a magnetic field,charged particles from the solar wind cannot impact theatmosphere directly, but are instead deflected by themagnetic field and aggregate to form the Van Allen belts.The Van Allen Radiation Belt is a torus of energeticcharged particles (plasma) around Earth, trapped by Earth’smagnetic field. The Van Allen belts are closely related tothe poles where particles strike the upper atmosphere andfluoresce.The Van Allen belts consist of an inner beltcomposed primarily of protons and an outer belt composedmostly of electrons. Radiation within the Van Allen beltscan occasionally damage satellites passing through them.TheVan Allen belts form arcs around the Earth with their tipsnear the north and south poles. The most energetic particles

can ‘leak out’ of the belts and strike the Earth’s upperatmosphere, causing a bright streak of light that sweepsthe sky, known by name aurorae borealis in the northernhemisphere and aurorae australis in the southernhemisphere.• Apastron : The point of greatest separation between

two stars, which are in orbit around each other. (Incase of Binary stars) Opposite of periastron

• Cataclysmic variable (CV) : Binary star systems withone white dwarf star and one normal star, in close orbitabout each other. Material from the normal star fallsonto the white dwarf, creating a burst of X-rays.

• Cepheid variables are a type of variable stars, whichexhibits a regular pattern of changing brightness as afunction of time. The period of the pulsation patternis directly related to the star’s intrinsic brightness. Thus,Cepheid variables are a powerful tool for determiningdistances in modern astronomy

• S.Chandrasekhar, (1910-1995) Indian astrophysicistrenowned for creating theoretical models of whitedwarf stars, among other achievements. His equationsexplained the underlying physics behind the creationof white dwarfs, neutron stars and other compactobjects. Chandra X–ray Observatory (CXO) Oneof NASA’s Great Observatories in Earth orbit,launched in July 1999, and named after S.Chandrasekhar. It was previously named the AdvancedX-ray Astrophysics Facility (AXAF).

• Evolved star: A star near the end of its lifetime whenmost of its fuel has been used up. This period of thestar’s life is characterized by loss of mass from its surfacein the form of a stellar wind.

• Flux : A measure of the amount of energy given off byan astronomical object over a fixed amount of time andarea. Because the energy is measured per time and area,flux measurements make it easy for astronomers tocompare the relative energy output of objects with verydifferent sizes or ages.

• Hawking radiation (S.W. Hawking; 1973) :A theoryfirst proposed by British physicist Stephen Hawking,that due to a combination of properties of quantummechanics and gravity, under certain conditions blackholes can seem to emit radiation.

• Hawking temperature: The temperature inferred for ablack hole based on the Hawking radiation detected fromit.

• Spörer’s law states that ‘as the sunspot cycleprogresses, the number of sunspots increases and theymove closer to the equator of the Sun.

• Most of solar flares occur around sunspots, whereintense magnetic fields emerge from the Sun’s surfaceinto the corona.

• The Schwabe solar cycle or Schwabe-Wolf cycle is theeleven-year cycle of solar activity of the sun by way ofsolar spots,solar flares etc.

• Spörer’s law predicts the variation of sunspot latitudesduring a solar cycle. It was discovered by Englishastronomer Richard Christopher Carrington around 1861.Carrington’s work was refined by German astronomerGustav Spörer.

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A planetary system consists of the various non-stellarobjects orbiting a star such as planets, moons, asteroids,meteoroids, comets, and cosmic dust. The Sun and itsplanetary system, which includes Earth, is known asthe Solar System.

ORIGIN AND EVOLUTION

Planetary systems around sun-like stars aregenerally believed to form as part of the same processwhich results in star formation. Some early theoriesinvolved another star passing extremely close to the sun,and drawing material out from it which then coalescedto form the planets. However, the probability of such anear collision is now known to be far too low to makethis a viable model. Accepted theories today argue thatplanetary systems form from a solar nebula.Someplanetary systems are very unlike our own, however:planetary systems around pulsars have been inferredfrom slight variations in the period of the pulses ofelectromagnetic radiation. Pulsars are formed in violentsupernova explosions, and a normal planetary systemcould not possibly survive such a blast - planets wouldeither evaporate, or the sudden loss of most of the massof the central star would see them escape thegravitational hold of the star. One theory is that existingstellar companions were almost entirely evaporated bythe supernova blast, leaving behind planet-sized bodies.Alternatively, planets may somehow form in theaccretion disk surrounding pulsars.

Solar System - The Sun and its planetary system,the first such system discoveredPSR 1257+12 - the first extrasolar planetary systemdiscovered, the first pulsar planetary system discovered,the first multi exoplanet system discovered, the firstmulti planet system with a pulsar discoveredUpsilon Andromedae - the first multiplanet extrasolarplanetary system discovered around a main sequencestar, found to be so in April 1999PSR B1620-26 - the first multistar planetary systemdiscovered55 Cancri - the largest extra solar planetary systemdiscovered (4 planets, as of August 2004, along witha distant stellar companion)Gliese 876 - the first system around a red dwarf starand the first discovered to be in an orbital resonanceHD 69830 - found to have three Neptune-massplanets and an asteroid belt, all within 1 AU2M1207 - the first imaged system and the first browndwarf system with a planet discovered

PLANETARY SYSTEMCha 110913 - the first substellar/planetary systemdiscovered

SOLAR SYSTEM :

Major features of the Solar System are: The Sun, theeight planets, the asteroid belt containing the dwarf planetCeres, outermost there is the dwarf planet Pluto (the dwarfplanet Eris not shown), and a comet.

The Solar System or solar system comprises the Sunand the retinue of celestial objects gravitationally boundto it: the eight planets, their 162 known moons, threecurrently identified dwarf planets and their four knownmoons, and thousands of small bodies. This last categoryincludes asteroids, meteoroids, comets, and interplanetarydust.

The principal component of the Solar System is theSun a main sequence G2 star that contains 99.86% of thesystem’s known mass and dominates it gravitationally.

Because of its large mass, the Sun has an interiordensity high enough to sustain nuclear fusion, releasingenormous amounts of energy, most of which is radiatedinto space in the form of electromagnetic radiation,including visible light.

The Sun’s two largest orbiting bodies, Jupiter andSaturn, account for more than 90% of the system’sremaining mass. (The currently hypothetical Oort cloud,should its existence be confirmed, would also hold asubstantial percentage).

In broad terms, the charted regions of the SolarSystem consist of the Sun, four rocky bodies close to itcalled the terrestrial planets, an inner belt of rocky asteroids,four gas giant planets, and an outer belt of small, icy bodiesknown as the Kuiper belt.

In order of their distances from the Sun, the planetsare Mercury ( ), Venus ( ), Earth ( ), Mars ( ), Jupiter( ), Saturn ( ), Uranus ( ), and Neptune ( ). Allplanets but two are in turn orbited by natural satellites(usually termed “moons” after Earth’s Moon), and everyplanet past the asteroid belt is encircled by planetary ringsof dust and other particles. The planets, with the exceptionof Earth, are named after gods and goddesses from Greco-Roman mythology.

From 1930 to 2006, Pluto ( ), the largest knownKuiper belt object, was considered the Solar System’s ninthplanet. However, in 2006 the International AstronomicalUnion (IAU) created an official definition of the term“planet”.

Under this definition, Pluto is reclassified as a dwarfplanet, and there are eight planets in the Solar System.

In addition to Pluto, the IAU currently recognizes twoother dwarf planets: Ceres ( ) , the largest object in theasteroid belt, and Eris, which lies beyond the Kuiper belt


CONCEPTS OF GEOGRAPHYin a region called the scattered disc. Of the known dwarfplanets, only Ceres has no moons.

LAYOUT :

Most objects in orbit round the Sun lie within thesame shallow plane, called the ecliptic, which is roughlyparallel to the Sun’s equator.

The planets lie very close to the ecliptic, while cometsand kuiper belt objects often lie at significant angles to it.All of the planets, and most other objects, also orbit withthe Sun’s rotation in a counter-clockwise direction as viewedfrom a point above the Sun’s north pole.

There is a direct relationship between how far away aplanet is from the Sun, and how quickly it orbits. Mercury,with the smallest orbital circumference, travels the fastest,while Neptune, being much farther from the Sun, travelsmore slowly.

A planet’s distance from the Sun varies in the courseof its year. Its closest approach to the Sun is known as itsperihelion, while its farthest point from the Sun is calledits aphelion.

Though planets follow nearly circular orbits, withperihelions roughly equal to their aphelions, many comets,asteroids and objects of the Kuiper belt follow highlyelliptical orbits, with large differences between perihelionand aphelion.

Astronomers most often measure distances within thesolar system in astronomical units, or AU. One AU is theaverage distance between the Earth and the Sun, or roughly149 598 000 km (93,000,000 mi).

Informally, the Solar System is sometimes divided intoseparate “zones”; the first zone, known as the inner SolarSystem, comprises the inner planets and the main asteroidbelt.

The outer solar system is sometimes defined aseverything beyond the asteroids; however, it is also the nameoften given to the region beyond Neptune, with the gasgiants as a separate “middle zone.

Planets, dwarf planets, and small solar system bodies

In a decision passed by the International AstronomicalUnion General Assembly on August 24, 2006, the objectsin the Solar System were divided into three separate groups:planets, dwarf planets and small solar system bodies.

Under this classification, a planet is any body in orbitaround the Sun that a) has enough mass to form itselfinto a spherical shape and b) has cleared its immediateneighborhood of all smaller objects. Eight objects in theSolar System currently meet this definition; they areMercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus,and Neptune.

Dwarf planet is a newly defined classification forastronomical objects. The key difference between planets

and dwarf planets is that while both are required toorbit the Sun and be of large enough mass that theirown gravity pulls them into a nearly round shape,dwarf planets are not required to clear theirneighborhood of other celestial bodies. Three objectsin the solar system are currently included in thiscategory; they are Pluto (formerly considered a planet),the asteroid Ceres, and the scattered disc object Eris.

The IAU will begin evaluating other known objectsto see if they fit within the definition of dwarf planets.The most likely candidates are some of the larger asteroidsand several Trans-Neptunian Objects such as Sedna, Orcus,and Quaoar.

The remainder of the objects in the Solar System wereclassified as small solar system bodies. A small solarsystem body (SSSB) is a term defined in 2006 by theInternational Astronomical Union to describe Solar Systemobjects which are neither planets nor dwarf planets.

All other objects ... orbiting the Sun shall be referred tocollectively as “Small Solar System Bodies” .... These currently includemost of the Solar System asteroids, most Trans-Neptunian Objects(TNOs), comets, and other small bodies.

AGE

Using radiometric dating, scientists can estimate thatthe solar system is 4.6 billion years old.

The oldest rocks on Earth are approximately 3.9 billionyears old. Rocks this old are rare, as the Earth’s surface isconstantly being reshaped by erosion, volcanism and platetectonics.

To estimate the age of the solar system scientists mustuse meteorites, which were formed during the earlycondensation of the solar nebula. The oldest meteorites(such as the Canyon Diablo meteorite) are found to havean age of 4.6 billion years, hence the solar system must beat least 4.6 billion years old.

The current hypothesis of Solar System formation isthe nebular hypothesis, first proposed in 1755 by ImmanuelKant and independently formulated by Pierre-SimonLaplace.

Inner planets :

The four inner or terrestrial planets are characterisedby their dense, rocky composition, few or no moons, andlack of ring systems.

They are composed largely of minerals with highmelting points such as silicates to form the planets’ solidcrusts and semi-liquid mantles, and metallic dust grains suchas iron, which forms their cores.

Three of the four inner planets have atmospheres. Allhave impact craters, and all but one possess tectonic surface


CONCEPTS OF GEOGRAPHYfeatures, such as rift valleys and volcanoes.

The term inner planet should not be confused withinferior planet, which designates those planets which arecloser to the Sun than the Earth is (i.e. Mercury and Venus).

THE FOUR INNER PLANETS ARE

Mercury :

Mercury (0.4 AU), the closest planet to the Sun, isalso the least massive of the planets, at only 0.055 Earthmasses.

Mercury has a very thin atmosphere consisting ofatoms blasted off its surface by the solar wind. BecauseMercury is so hot, these atoms quickly escape into space.Thus in contrast to the Earth and Venus whoseatmospheres are stable, Mercury’s atmosphere is constantlybeing replenished.

Mercury is surrounded by an extremely small amountof helium, hydrogen, oxygen, and sodium. This envelopeof gases is so thin that the greatest possible atmosphericpressure (force exerted by the weight of gases) on Mercurywould be about 0.000000000002 kgf/cm² (0.00000000003psi or 0.2 µPa).

The atmospheric pressure on the Earth is about 1.03kgf/cm² (14.7 psi or 101 kPa). It has no natural satellite.

Its relatively large iron core and thin mantle have notyet been adequately explained. Hypotheses include that itsouter layers were stripped off by a giant impact, and thatit was prevented from fully accreting by the Sun’s gravity.

The MESSENGER probe should aid in resolving thisissue when it arrives in Mercury’s orbit in 2011.

Venus :

Venus (0.7 AU), the first truly terrestrial planet, is ofcomparable mass to the Earth (0.815 Earth masses), and,like Earth, possesses a thick silicate mantle around an ironcore, as well as a substantial atmosphere and evidence ofone-time internal geological activity, such as volcanoes.

However, it is much drier than Earth and itsatmosphere is 90 times as dense and is composedoverwhelmingly (96.5%) of carbon dioxide.

Unlike Earth, evidence suggests that Venus’s crust isnot divided into tectonic plates but instead comprises asingle very thick rind.]

Venus has no natural satellite.

It is the hottest planet, despite being farther from thesun than Mercury, with temperatures reaching more than400 degrees Celsius. This is most likely because of theamount of greenhouse gases in the atmosphere.

Earth

The largest and densest of the inner planets, Earth(1 AU) is also the only one to demonstrate unequivocal

evidence of current geological activity.

Earth is the only planet known to have life. Itsliquid hydrosphere, unique among the terrestrials, isprobably the reason Earth is also the only planet wheremulti-plate tectonics has been observed, because wateracts as a lubricant for subduction.]

Its atmosphere is radically different from the otherterrestrials, having been altered by the presence of lifeto contain 21 percent free oxygen.

Its satellite, the Moon, is sometimes considered aterrestrial planet in a co-orbit with its partner, becauseits orbit around the Sun never actually loops back onitself when observed from above.

The Moon possesses many features in commonwith other terrestrial planets, though it lacks an ironcore.

Mars

Mars (1.5 AU), at only 0.107 Earth masses, is lessmassive than either Earth or Venus. It possesses atenuous atmosphere of carbon dioxide.

Its surface, peppered with vast volcanoes and riftvalleys such as Valles Marineris, shows that it was oncegeologically active and recent evidence suggests this mayhave been true until very recently.

Mars possesses two tiny moons (Deimos andPhobos) thought to be captured asteroids.

Asteroid belt :

Asteroids are mostly small solar system bodies thatare composed in significant part of rocky, non-volatileminerals.

The main asteroid belt occupies the orbit betweenMars and Jupiter, between 2.3 and 3.3 AU from the Sun.

It is thought to be the remnants of a smallterrestrial planet that failed to coalesce because of thegravitational interference of Jupiter.

Asteroids range in size from hundreds ofkilometers to as small as dust. All asteroids save thelargest, Ceres, are classified as small solar system bodies;however, a number of other asteroids, such as Vestaand Hygeia, could potentially be reclassed as dwarfplanets if it can be conclusively shown that they arespherical.

The asteroid belt contains tens of thousands - andpotentially millions - of objects over one kilometre indiameter.

However, despite their large numbers, the totalmass of the main belt is unlikely to be more than athousandth of that of the Earth

In contrast to its various depictions in sciencefiction, the main belt is very sparsely populated;


CONCEPTS OF GEOGRAPHYspacecraft routinely pass through without incident.Asteroids with a diameter of less than 50 m are calledmeteoroids.

Ceres :

Ceres (2.77 AU) is the largest astronomical bodyin the asteroid belt and the only known dwarf planet inthis region.

It has a diameter of slightly under 1000 km, largeenough for its own gravity to pull it into a spherical shape.

Ceres was considered a planet when it was discoveredin the nineteenth century, but was reclassified as an asteroidas further observation revealed additional asteroids. It hassince been again reclassified as a dwarf planet.

Asteroid groups :

Asteroids in the main belt are subdivided into asteroidgroups and families based on their specific orbitalcharacteristics.

Asteroid moons are asteroids that orbit larger asteroids.They are not as clearly distinguished as planetary moons,sometimes being almost as large as their partners.

The asteroid belt also contains main-belt comets whichmay have been the source of Earth’s water.

Trojan asteroids are located in either of Jupiter’s L4or L5 points, (gravitationally stable regions leading andtrailing a planet in its orbit) though the term is alsosometimes used for asteroids in any other planetaryLagrange point as well.

The inner solar system is also dusted with rogueasteroids, many of which cross the orbits of the innerplanets.

Outer planets :

The four outer planets, or gas giants, (sometimescalled Jovian planets) are so large they collectively makeup 99 percent of the mass known to orbit the Sun.

Jupiter and Saturn are true giants, at 318 and 95 Earthmasses, respectively, and composed largely of hydrogen andhelium.

Uranus and Neptune are both substantially smaller,being only 14 and 17 Earth masses, respectively.

Their atmospheres contain a smaller percentage ofhydrogen and helium, and a higher percentage of “ices”,such as water, ammonia and methane.

For this reason some astronomers suggested thatthey belong in their own category, “Uranian planets,”or “ice giants.”

All four of the gas giants exhibit orbital debris rings,although only the ring system of Saturn is easily observablefrom Earth.

The term outer planet should not be confused with

superior planet, which designates those planets whichlie outside Earth’s orbit (thus consisting of the outerplanets plus Mars).

Jupiter :

Jupiter (5.2 AU), at 318 Earth masses, is 2.5 timesthe mass of all the other planets put together. Itscomposition of largely hydrogen and helium is not verydifferent from that of the Sun, and the planet has beendescribed as a “failed star”.

Jupiter’s strong internal heat creates a number of semi-permanent features in its atmosphere, such as cloud bandsand the Great Red Spot.

The four largest of its 63 satellites, Ganymede,Callisto, Io, and Europa (the Galilean satellites) shareelements in common with the terrestrial planets, such asvolcanism and internal heating. Ganymede, the largestsatellite in the Solar System, has a diameter larger thanMercury.

Saturn :

Saturn (9.5 AU), famous for its extensive ring system,has many qualities in common with Jupiter, including itsatmospheric composition, though it is far less massive, beingonly 95 Earth masses.

Two of its 56 moons, Titan and Enceladus, show signsof geological activity, though they are largely made of ice.

Titan, like Ganymede, is larger than Mercury; it isalso the only satellite in the solar system with asubstantial atmosphere, similar in composition to that ofthe atmosphere of the early Earth.

Uranus :

Uranus (19.6 AU) at 14 Earth masses, is the lightestof the outer planets. Uniquely among the planets, it orbitsthe Sun on its side; its axial tilt lies at over ninety degreesto the ecliptic.

Its core is remarkably cold (compared with the othergas giants; it is still several thousand degrees Celsius) andradiates very little heat into space.

Uranus has 27 satellites, the largest being Titania,Oberon, Umbriel, Ariel and Miranda.

Neptune :

Neptune (30 AU), though slightly smaller than Uranus,it is denser and slightly more massive, at 17 Earth masses, andradiates more internal heat than Uranus, but not as much asJupiter or Saturn.

Its peculiar ring system is composed of a number ofdense “arcs” of material separated by gaps.

Neptune has 13 moons. The largest, Triton, isgeologically active, with geysers of liquid nitrogen, and isthe only large satellite to revolve around its host planetin a prograde (clockwise) motion.


CONCEPTS OF GEOGRAPHYKuiper belt :

The area beyond Neptune, often referred to as theouter solar system or simply the “trans-Neptunian region”,is still largely unexplored.

This region’s first formation, which actually beginsinside the orbit of Neptune, is the Kuiper belt, a greatring of debris, similar to the asteroid belt but composedmainly of ice and far greater in extent, which lies between30 and 50 AU from the Sun.

This region is thought to be the place of origin forshort-period comets, such as Halley’s comet.

Though it is composed mainly of small solar systembodies, many of the largest Kuiper belt objects could soonbe reclassified as dwarf planets.

There are estimated to be over 100,000 Kuiper beltobjects with a diameter greater than 50 km; however, thetotal mass of the Kuiper belt is relatively low, perhaps barelyequalling the mass of the Earth.

Many Kuiper belt objects have multiple satellites andmost have orbits that take them outside the plane of theecliptic.

Pluto and Charon :

Pluto (39 AU average), is the largest known object inthe Kuiper belt and was previously accepted as the smallestplanet in the Solar System.

In 2006, it was reclassified as a dwarf planet by theAstronomers Congress organized by the InternationalAstronomers Union (IAU).

Pluto has a relatively eccentric orbit inclined 17 degreesto the ecliptic plane and ranging from 29.7 AU from theSun at perihelion (within the orbit of Neptune) to 49.5 AUat aphelion.

Prior to the 2006 redefinitions, Charon was considereda moon of Pluto, but in light of the redefinition it isunclear whether Charon will continue to be classified as amoon of Pluto or as a dwarf planet itself.

Charon does not exactly orbit Pluto in a traditionalsense; Charon is about one-tenth the mass of Pluto andthe center of gravity of the pair is not within Pluto.

Both bodies orbit a barycenter of gravity above thesurface of Pluto (in empty space), making Pluto-Charon abinary system. Two much smaller moons, Nix and Hydra,orbit Pluto and Charon.

Those Kuiper belt objects which, like Pluto, possess a3:2 orbital resonance with Neptune (ie, they orbit twicefor every three Neptunian orbits) are called Plutinos.

Other Kuiper belt objects have different resonantorbits (2:1, 4:7, 3:5 etc) and are grouped accordingly.

The remaining Kuiper belt objects, in more “classical”orbits, are classified as Cubewanos, after the first of their

kind to be discovered, 1992 QB1.

Comets :

Comets are small solar system bodies (usually onlya few kilometres across) composed largely of volatileices, which possess highly eccentric orbits, generallyhaving a perihelion within the orbit of the inner planetsand an aphelion far beyond Pluto.

When a comet approaches the Sun, its icy surfacebegins to sublimate, or boil away, creating a coma; a longtail of gas and dust which is often visible with the nakedeye.

There are two basic types of comet: short-periodcomets, with orbits less than 200 years, and long-periodcomets, with orbits lasting thousands of years.

Short-period comets are believed to originate in theKuiper belt, while long period comets, such as Hale-Boppare believed to originate in the Oort Cloud.

Some comets with hyperbolic orbits may originateoutside the solar system. Old comets that have had mostof their volatiles driven out by solar warming are oftencategorized as asteroids.

Centaurs are icy comet-like bodies that have less-eccentric orbits so that they remain in the region betweenJupiter and Neptune.

The first centaur to be discovered, 2060 Chiron, hasbeen called a comet since it has been shown to develop acoma just as comets do when they approach the sun.]

Scattered disc :

Overlapping the Kuiper belt but extending muchfurther outwards is the scattered disc.

Scattered disc objects are believed to have beenoriginally native to the Kuiper belt, but were ejected intoerratic orbits in the outer fringes by the gravitationalinfluence of Neptune’s outward migration.

Most scattered disc objects have perihelia within theKuiper belt but aphelia as far as 150 AU from the Sun.Their orbits are also highly inclined to the ecliptic plane,and are often almost perpendicular to it.

Some astronomers, such as Kuiper belt co-discovererDavid Jewitt, consider the scattered disc to be merelyanother region of the Kuiper belt, and describe scattereddisc objects as “scattered Kuiper belt objects.

Eris :

Eris (68 AU average) is the largest known scattereddisc object and was the cause of the most recent debateabout what constitutes a planet since it is at least 5% largerthan Pluto with an estimated diameter of 2400 km(1500 mi).

It is now the largest of the known dwarf planets.Ithas one moon, Dysnomia.


CONCEPTS OF GEOGRAPHYThe object has many similarities with Pluto: its orbit

is highly eccentric, with a perihelion of 38.2 AU(roughly Pluto’s distance from the Sun) and an aphelionof 97.6 AU, and is steeply inclined to the ecliptic plane,at 44 degrees, more so than any known object in thesolar system except the newly-discovered object 2004XR190 (also known as “Buffy”) and is believed to consistlargely of rock and ice.

Farthest regions :

The point at which the solar system ends andinterstellar space begins is not precisely defined, since itsouter boundaries are delineated by two separate forces: thesolar wind and the Sun’s gravity.

The solar wind extends to a point roughly 130 AUfrom the Sun, whereupon it surrenders to the surroundingenvironment of the interstellar medium.

It is generally accepted, however, that the Sun’s gravityholds sway to the Oort cloud. This great mass of up to atrillion icy objects, currently hypothetical, is believed to bethe source for all long-period comets and to surround thesolar system like a shell from 50,000 to 100,000 AU beyondthe Sun, or almost a quarter the distance to the next starsystem.

The vast majority of the solar system, therefore, iscompletely unknown; however, recent observations of boththe solar system and other star systems have led to anincreased understanding of what is or may be lying at itsouter edge.

Sedna :

Sedna is a large, reddish Pluto-like object with agigantic, highly elliptical orbit that takes it from about 76AU at perihelion to 928 AU at aphelion and takes 12,050years to complete.

Mike Brown, who discovered the object in 2003,asserts that it cannot be part of the scattered disc or theKuiper Belt as it has too distant a perihelion to have beenaffected by Neptune’s migration.

He and other astronomers consider it to be the firstin an entirely new population, one which also may includethe object 2000 CR105, which has a perihelion of 45 AU,an aphelion of 415 AU, and an orbital period of 3420years.

Sedna is very likely a dwarf planet, though its shapehas yet to be determined with certainty.

Heliopause :

The heliosphere expands outward in a great bubbleto about 95 AU, or three times the orbit of Pluto.

The edge of this bubble is known as the terminationshock; the point at which the solar wind collides with theopposing winds of the interstellar medium.

Here the wind slows, condenses and becomes more

turbulent, forming a great oval structure known as theheliosheath that looks and behaves very much like a comet’stail; extending outward for a further 40 AU at its stellar-windward side, but tailing many times that distance inthe opposite direction.

The outer boundary of the sheath, the heliopause,is the point at which the solar wind finally terminates,and one enters the environment of interstellar space.

Beyond the heliopause, at around 230 AU, lies thebow shock, a plasma “wake” left by the Sun as it travelsthrough the Milky Way.

Galactic context

The solar system is located in the Milky Waygalaxy, a barred spiral galaxy with a diameter estimatedat about 100,000 light years containing approximately200 billion stars.

Our Sun resides in one of the Milky Way’s outerspiral arms, known as the Orion Arm or Local Spur.

The immediate galactic neighborhood of the solarsystem is known as the Local Fluff, an area of dense cloudin an otherwise sparse region known as the Local Bubble,an hourglass-shaped cavity in the interstellar mediumroughly 300 light-years across.

The bubble is suffused with high-temperature plasmathat suggests it is the product of several recent supernovae.

Estimates place the solar system at between 25,000and 28,000 light years from the galactic center. Its speed isabout 220 kilometres per second, and it completes onerevolution every 226 million years.

The apex of solar motion—that is, the direction inwhich the Sun is heading—is near the current location ofthe bright star Vega. At the galactic location of the solarsystem, the escape velocity with regard to the gravity ofthe Milky Way is about 1000 km/s.

Presumed location of the solar system within ourgalaxy

Discovery and exploration

The first exploration of the solar system wasconducted by telescope, with astronomers learning that theMoon and other planets possessed such Earthlike featuresas craters, ice caps, and seasons.

Galileo Galilei was the first to discover physical detailsabout the individual bodies of the Solar System. Hediscovered that the Moon was cratered, that the Sun wasmarked with sunspots, and that Jupiter had four satellitesin orbit around it.

Christiaan Huygens followed on from Galileo’sdiscoveries by discovering Saturn’s moon Titan and theshape of the rings of Saturn.

Giovanni Domenico Cassini later discovered four more


CONCEPTS OF GEOGRAPHYmoons of Saturn, the Cassini division in Saturn’s rings,and the Great Red Spot of Jupiter.

In 1682, Edmund Halley realised that repeatedsightings of a comet were in fact recording the sameobject, returning regularly once every 75-6 years. Thisproved once and for all that comets were notatmospheric phenomena, as had been previouslythought, and was the first evidence that anything otherthan the planets orbited the Sun.

In 1781, William Herschel was looking for binarystars in the constellation of Taurus when he observedwhat he thought was a new comet. In fact, its orbitrevealed that it was a new planet, Uranus, the first everdiscovered.

In 1801, Giuseppe Piazzi discoverd Ceres, a smallworld between Mars and Jupiter that was initially considereda new planet. However, subsequent discoveries of thousandsof other small worlds in the same region led to theireventual separate reclassification: asteroids.

In 1846, discrepancies in the orbit of Uranus led manyto suspect a large planet must be tugging at it from fartherout. Urbain Le Verrier’s calculations eventually led to thediscovery of Neptune.

Further discrepancies in the orbits of the planets ledPercival Lowell to conclude yet another planet, “Planet X”must still be out there. After his death, his LowellObservatory conducted a search, which ultimately led toClyde Tombaugh’s discovery of Pluto in 1930.

Pluto was, however, found to be too small to havedisrupted the orbits of the outer planets, and its discoverywas therefore coincidental. Like Ceres, it was initiallyconsidered to be a planet, but after the discovery of manyother similarly sized objects in its vicinity it was eventuallyreclassified as a Kuiper belt object.

In 1992, astronomers David Jewitt of the Universityof Hawaii and Jane Luu of the Massachusetts Institute ofTechnology discovered 1992 QB1, the first object foundbeyond Neptune in 62 years. This object proved to bethe first of a new population, which came to be known asthe Kuiper Belt; an icy analogue to the asteroid belt ofwhich such objects as Pluto and Charon were deemed apart.

Many of the largest of these objects, such as Chaos,Quaoar, Varuna and Ixion, where discovered by astronomerMike Brown.

In 2005, Mike Brown announced the discovery of Eris,a Scattered disc object larger than Pluto and the largestobject discovered in the solar system since Neptune.

Observations by spacecraft

Since the start of the space age, a great deal ofexploration has been performed by unmanned spacemissions that have been organized and executed by various

space agencies.

The first probe to land on another solar systembody was the Soviet Union’s Luna 2 probe, whichimpacted on the Moon in 1959.

Since then, increasingly distant planets have beenreached, with probes landing on Venus in 1965, Mars in1976, the asteroid 433 Eros in 2001, and Saturn’s moonTitan in 2005. Spacecraft have also made close approachesto other planets: Mariner 10 passed Mercury in 1973.

The first probe to explore the outer planets was Pioneer10, which flew by Jupiter in 1973. Pioneer 11 was the firstto visit Saturn, in 1979.

The Voyager probes performed a grand tour of theouter planets following their launch in 1977, with bothprobes passing Jupiter in 1979 and Saturn in 1980 – 1981.Voyager 2 then went on to make close approaches to Uranusin 1986 and Neptune in 1989.

The Voyager probes are now far beyond Neptune’sorbit, and astronomers anticipate that they will encounterthe heliopause which defines the outer edge of the solarsystem in the next few years.

No Kuiper belt object has been visited by a man-madespacecraft. Launched in 19 January 2006, the New Horizonsis currently enroute to becoming the first man-madespacecraft to explore this area. This unmanned mission isscheduled to fly by Pluto in July 2015. Should it provefeasible, the mission will then be extended to observe anumber of other Kuiper belt objects.

Following is a list of solar system objects by orbit,ordered by increasing distance from the Sun. Most namedobjects in this list have a diameter of 500 km or more.

The Sun, a spectral class G2V star . The inner solarsystem and the terrestrial planetsMercury

Mercury - crosser asteroidsVenus

Venusosser asteroidsVenus’ quasi-satellite

EarthMoon (Luna)Possible Kordylewski CloudNear-Earth asteroidsEarth-crosser asteroidsEarth’s quasi-satellites

MarsDeimosPhobosMars trojansMars-crosser asteroidsAsteroid belt and surrounds


CONCEPTS OF GEOGRAPHYCeres, a dwarf planet in the asteroid beltAsteroids in the Main Asteroid Belt, between

the orbits of Mars and JupiterPallas, Juno,Vesta

Jupiter SatellitesIo -Europa -Ganymede -CallistoJupiter’s trojan asteroids

SaturnTethys -Dione -Rhea -Titan ---apetus -EnceladusMimas -Hyperion -

UranusAriel -Umbriel -Miranda -Titania -Oberon

NeptuneTriton -Nereid -Proteus -Trans-Neptunian objects beyond the orbit of

NeptuneKuiper belt objects (KBOs)Pluto, a dwarf planet and plutinoCharon -Nix -Hydra -Plutinos -90482 Orcus -

TwotinoScattered disc objectsEris, a dwarf planetDysnomia( Sedna (possibly inner Oort Cloud)

The solar system also contains:Comets (icy bodies with eccentric orbits). periodic comets non-periodic cometsSmall objects, including:MeteoroidsDust, including interstellar dust.Helium Focusing Cone, around the Sun.

Planets size by mass.

Following is a list of solar system objects moremassive than 1021 kilograms (one Yottagram [Yg]).Even the least massive of these objects is anapproximate sphere. Eris, a new trans-Neptunianobject, is larger than Pluto but has an undeterminedmass. An estimate is listed.

Zettagram range

Objects of mass between 1018 kg to 1021 kg (1to 1000 Zettagrams (Zg) ). The larger objects in thisrange, such as Tethys, 1 Ceres, and Mimas, haverelaxed to an equilibrium oblate spheroid due to theirgravity, while the less massive (e. g. Amalthea andJanus) are roughly rounded, but not spherical, dubbed“irregular”.

All the spheroidal bodies have some polarflattening due to the centrifugal force from their rotation,but a characteristic feature of the “irregular”-shapedbodies is that there is a significant difference in thelength of their two equatorial diameters.

Exagram range

Objects of mass between 1015 kg to 1018 kg (1 to1000 Exagrams (Eg) ). These objects are not spherical

Petagram range

Objects of mass between 1012 kg to 1015 kg (lessthan 1000 Petagrams (Pg) ). A few of the smallest of theirregular satellites of the gas planets are listed here, aswell as the largest near-Earth asteroids due to unusualinterest for their nearness. (See also: list of NEAs bydistance from Sun.) Other NEOs that are not asteroids(e. g. inner-solar-system comets) are almost always lessmassive than 1 Pg.

Teragram range

Objects of mass between 109 kg to 1012 kg (lessthan 1000 Teragrams (Tg) ). Currently all the bodieslisted here are Near-Earth asteroids (See also: list ofNEAs by distance from Sun.)

Gigagram range

Objects of mass between 106 kg to 109 kg (lessthan 1000 Gigagrams (Gg) ). Currently all the objectslisted here are Near-Earth asteroids (See also: list ofNEAs by distance from Sun.)



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CONCEPTS OF GEOGRAPHYAstronomical symbols are symbols used to represent various celestial objects, theoretical constructs and observational

events in astronomy. The symbols listed here are commonly used by professional and amateur astronomers.

PLANETS Name symbol Unicode image Represented by image

Mercury � U+263F

Mercury's winged helmet and caduceus

Venus ♀ U+2640

Venus' hand mirror

Earth � U+2295

globe with equator and a meridian

Mars ♂ U+2642

Mars' shield and spear

Jupiter � U+2643

Jupiter's thunderbolt or eagle

Saturn � U+2644

Saturn's sickle or scythe

Uranus

From a symbol for platinum, a combination of the symbols for Mars and the Sun

Neptune � U+2646

Neptune's trident

DWARF PLANETS Name symbol Unicode image Represented by image

Ceres

Handle-down sickle; cf. the handle-up sickle symbol of Saturn

Pluto � U+2647

PL monogram for Pluto and Percival Lowell

Eris No symbol Unlikely to gain an official symbol

ASTEROIDS Name symbol Unicode image Represented by image

2 Pallas

Modified symbol for female?

3 Juno

Peacock (totem of Juno).

4 Vesta

Hearth or fire-altar.

5 Astraea

Anchor (inverted), or possibly scales of justice.

6 Hebe

Cup

7 Iris

Rainbow with star under it (asteroid means star-like)

8 Flora

Stylised flower

9 Metis

Eye, with star above it (Asteroid means star-like)

10 Hygeia

Rod of Asclepius

OTHER CELESTIAL BODIES Name symbol Unicode image Represented by image

Sun � U+2609

Solar symbol

Moon � U+263D

A crescent moon


CONCEPTS OF GEOGRAPHYOTHER SYMBOLS

Name symbol Unicode image Represented by image comet � U+2604

ascending node � U+260A

descending node � U+260B

conjunction � U+260C

opposition � U+260D

ZODIAC

The term zodiac (from Greek MEANING”circle oflittle animals) denotes several places where a circle of twelveanimals occurs. Indo-European cultures developed azodiac of twelve signs associated with a yearly cycle andwith constellations of stars that lie along the apparent pathof the Sun across the heavens (the ecliptic). Likewise inChinese astrology, months and years pass through a cycleof twelve animals that imply certain fortunes or misfortunesrelated to events occurring within those signs.

Below are the Roman names of the signs of thezodiac (with the ecliptic longitudes of their first points

Wheel of the zodiac: 6th century mosaic pavementadapting Greek-Byzantine elements from a synagogue, BeitAlpha, Israel

Aries (0°)Taurus (30°)Gemini (60°)Cancer (90°)Leo (120°)Virgo (150°)Libra (180°)Scorpius (210°)Sagittarius (240°)Capricornus (270°)Aquarius (300°)Pisces (330°)

Traditional Hindu astrology has a siderial coordinatezodiac system with twelve signs. The names of the Hinduzodiacal signs, or râúis, are similar to Graeco-Babyloniansigns, apparently as a result of Indo-Greek contact:

meca “ram” (Aries)v[cabha “bull” (Taurus)mithuna “a pair” (Gemini)karka “crab” (Cancer)siCha “lion” (Leo)kanyâ “girl” (Virgo)tula, from tulâ “balance” (Libra)âli “scorpion” (Scorpius), also kaurpi, loaned from

the Greekkârmuka, câpa, dhanus “bow, arc”, câpin

“armed with a bow” (Sagittarius)eGa, m[ga “antelope”, also makara “sea-monster”

(Capricornus)kumbha “pitcher, water-pot” (Aquarius)matsya “fish”, also jhaca, timi, mîna after

specific kinds of fish (Pisces)



Astronomical units of length :Astronomers use a number of different length units

for different objects. The length unit used is typicallydetermined by two criteria:

the unit should create manageable numbersthe unit should be easily derivable from observationThe distances are closely related to the cosmic

distance ladder.Units used for various astronomical distances

Astronomical Range : Typical UnitsDistances to satellites : kilometresPlanetary distances : astronomical unitsDistances to nearby stars : light years, or parsecsDistances at the galactic scale: kiloparsecsDistances to nearby galaxies : megaparsecs

The distances to distant galaxies are typically notquoted in distance units at all, but rather in terms ofredshift. The reasons for this are that converting redshiftto distance requires knowledge of the Hubble constantwhich was not accurately measured until the early 21st

The dates can vary by as much as 2 days from year to year, depending on the cycle of leap years.

century.Light-year1 light yearInternational units9.461×1015 m = 9.461×1012 km9.461×1018 mm = 94.607×1024 Å63.241×103 AU = 1 LYUS customary / Imperial units :372.47×1015 in = 31.039×1015 ft10.346×1015 yd = 5.879×1012 mi

A light-year or lightyear, symbol ly, is the distance lighttravels in vacuum in one Julian year. Units related to thelight year are the light-minute and light-second, thedistance light travels in a vacuum in one minute and onesecond, respectively. Since the speed of light is definedas 299,792,458 metres per second, a light-second is exactly299,792,458 m in length and a light-minute is exactly17,987,547,480 m. In contrast to the light-year, the lengthsof the light-minute and light-second are fixed with 100%precision.

Distances measured in fractions of a light-year usuallyinvolve objects within a star system.One astronomicalunit (the distance from the Sun to the Earth) is 1.58 ×10-5 light-years.


CONCEPTS OF GEOGRAPHYThe most distant space probe, Voyager 1, was 1.50

× 10-3 light-years away from Earth in September 2004. Ittook Voyager 27 years to cover that distance.

One kilolight-year, abbreviated “kly”, is one thousandlight-years, or 307 parsecs. Kilolight-years are typically usedto measure distances between parts of a galaxy.

The Galaxy is about 98 kilolight-years across.One megalight-year, abbreviated “Mly”, is one million

light-years, or 306,601 parsecs. Megalight-years are typicallyused to measure distances between neighboring galaxiesand galaxy clusters.

One gigalight-year, abbreviation “Gly”, is one billionlight-years — one of the largest distance measures used.One gigalight-year equals 306.601 million parsecs, orroughly one-thirteenth the distance to the horizon of theobservable universe (dictated by the cosmic backgroundradiation). Gigalight-years are typically used to measuredistances to supergalactic structures, such as clusters ofquasars or the Great Wall.

The Triangulum Galaxy (M33), at a little under 2.6megalight-years away, is the most distant object visible tothe naked eye.

The particle horizon (observable part) of theuniverse has a radius of about 13 gigalight-years.

Astronomical unit1 astronomical unit =

International units149.598×109 m = 149.598×106 km149.598×1012 mm = 1.496×1021 Å1 AU = 15.813×10"6 LYUS customary / Imperial units5.89×1012 in = 490.807×109 ft163.602×109 yd = 92.956×106 miThe astronomical unit (AU or au or a.u. or sometimes

ua) is a unit of length. It is approximately equal to themean distance between the Earth and Sun. The currentlyaccepted value of the AU is 149 597 870 691 ± 30 metres(about 150 million kilometres or 93 million miles).

Parsec1 parsec =International units30.857×1015 m = 30.857×1012 km30.857×1018 mm = 308.568×1024 Å206.265×103 AU = 3.262 LYUS customary / Imperial units1.215×1018 in = 101.236×1015 ft33.745×1015 yd = 19.174×1012 miThe parsec (symbol pc) is a unit of length used in

astronomy. It stands for “parallax of one arc second”.It is based on the method of trigonometric parallax, one

of the most ancient and standard methods of determiningstellar distances. The parallax of a star is half of theangular distance a star appears to move against thecelestial sphere compared to the orbit of the Eartharound the Sun (see the diagram at right). Equivalently, itis the angle subtended at a star by the radius of theEarth’s orbit. One parsec is defined to be the distance fromthe Earth to a star that has a parallax of 1 arcsecond. Itis, therefore, approximately:

360 × 60 × 60/(2ð) = 206,264.8062 AU

3.085 677 58 × 1016 m1.917 351 16 × 1013 miles3.261630751 light years

Miscellaneous factsReflected sunlight from the Moon’s surface takes 1.2

seconds to travel the 4.04 × 10"8 light years to Earth.It takes approximately 8.31 minutes for light to travel

from the Sun to the Earth (a distance of 1.58 × 10"5 light-years).

The most distant space probe, Voyager 1, was 13light hours (only 1.5 × 10"3 light years) away from Earthin September 2004. It took Voyager 27 years to cover thatdistance.

The nearest known star (other than the Sun), ProximaCentauri is 4.22 light years away.

Continuing at the speed above, it would take Voyager18000 years to cover a single light year, and 76000 yearsto cover the distance to Proxima Centauri.


CONCEPTS OF GEOGRAPHYThe center of our galaxy, the Milky Way, is about

8 kiloparsecs (26,000 light years) away. The Galaxy is about100,000 light years across.

The Triangulum Galaxy (M33), at 3.14 million lightyears away, is the most distant object visible to the nakedeye.

The nearest large galaxy cluster, the Virgo Cluster,is about 60 million light years away.

The particle horizon (observable part) of theuniverse has a radius of about 46 billion light years, butlight from the edge of the observable universe was emittedonly 13.7 billion years ago (the age of the universe). Thefigures differ because distant objects have continued torecede from us due to cosmological expansion (seeHubble’s law).

In the Disney movie Toy Story one character wasnamed Buzz Lightyear. Buzz referring to Buzz Aldrin -one of the first men on the moon, and Lightyear referringto astronomical distance

The symbol “ua” is recommended by the BureauInternational des Poids et Mesures , but in the UnitedStates and other anglophone countries the reverse usageis more common. The International Astronomical Unionrecommends “au” and international standard ISO 31-1uses “AU”.

STRUCTURE OF THE EARTH

The Earth is an oblate spheroid. It is composed ofa number of different layers as determined by deep drillingand seismic evidence.These layers are:

The core, which is approximately 7000 kilometers indiameter (3500 kilometers in radius) and is located at theEarth’s center. The mantle, which surrounds the core andhas a thickness of 2900 kilometers.

The crust floats on top of the mantle. It is composedof basalt rich oceanic crust and granitic rich continentalcrust.The structure of the interiors

Our knowledge of the interiors of the earth, , isderived from analyses of earthquake waves and the waythey behave. Several kinds of wave motions (P and S

waves) produced by the earthquakes called as body wavesbecause they travel through the solid body of the earth.Body waves are distinguished from surface waves, which movealong the free upper crust of the earth. Surface waves areof two types; they travel more or less together, but withdifferent motions. When an earthquake occurs,seismographs near the epicenter(the point on the Earth’ssurface that is directly above the point where an earthquake orother underground explosion originates. The epicenter is directly abovethe hypocenter, the actual location of the energy release insidethe earth) out to about 90° distance, are able to record bothP and S waves, but those at a greater distance no longerdetect the S wave. This is due to the fact that shear wavescannot pass through liquids. This was how Oldham provedthat the Earth had a liquid outer core in contrast to thesurrounding mantle, which is solid. The Moon has beenproven by seismic testing to have a solid core, because itconducts shear waves.

In addition, the two types of seismic wave behavedifferently, depending on the material. Compress ional Pwaves will travel and refract through both fluid and solid


CONCEPTS OF GEOGRAPHYmaterials. Shear S waves, however, cannot travel throughfluids like air or water. Fluids cannot support the side-to-side particle motion that makes S waves. The seismic wavesbend as they travel through different densities. The pathscurve because the different rock types found at differentdepths and different densities change the speed at whichthe waves travel.So in the core and therefore, P waves arenot directly received in a zone, known as shadow zone,between 1030 and 1430 distant from the focus. Also, S wavesare not received there because they do not travel throughthe liquid core. Only surface waves are received in thisshadow zone. Beyond 1430 only P waves passing throughthe core and surface waves traveling along the surface arereceived.The waves travel at different rates from a commonsource. So the time interval between their arrival at therecording station will also vary. Based on these observations,the earth’s interior has been divided into three layers –

crust, mantle and core.Cross-section of the whole Earth, showing the

complexity of paths of earthquake waves. The paths curvebecause the different rock types found at different depthschange the speed at which the waves travel. Solid linesmarked P are compressional waves; dashed lines marked Sare shear waves. S waves do not travel through the corebut may be converted to compressional waves (marked K)

on entering the core (PKP, SKS). Waves may be reflectedat the surface (PP, PPP, SS).The core

The core was the first internal structural element tobe identified. It was discovered in 1906 by R.D. Oldham.The core is composed principally of iron, with about 10percent alloy of oxygen or sulfur or nickel, or perhapssome combination of these three elements. It is composedof two layers: the outer and inner cores, composedmainly of heavy metallic NIFE {Nickel+Ferrum(iron)}. It accounts for 32% of the mass and 16% ofvolume of the planet Earth. This layer is also calledBARY SPHERE. The outer core is liquid and has adensity of about 11 grams per cubic centimeter. Itsurrounds the inner core and has an average thickness ofabout 2250 kilometers. The outer core is presumed to beliquid because it does not transmit shear (S) waves andbecause the velocity of compressional (P) waves that passthrough it is sharply reduced. The core is composed mostlyof iron (Fe) and is so hot that the outer core is molten,with about 10% sulphur (S).

The inner core is solid with a density of about 13grams per cubic centimeter and a radius of about 1220kilometers. The inner core is considered to be solid becauseof the reduced velocity of P waves passing through it. Thesulphur present in the core keeps it so hot that the outercore becomes molten and the inner core is under suchextreme pressure that it remains solid. Convection and therelease of heat from the Earth’s core drives furtherconvection in the mantle and Convection in the mantledrives plate tectonic motions of the sea floor andcontinents.

Data from earthquake waves, rotations and inertia ofthe whole Earth, magnetic-field dynamo theory, andlaboratory experiments on melting and alloying of iron allcontribute to the identification of the composition of theinner and outer core.THE MANTLE

The mantle is almost 2900 kilometers thick andcomprises about 83 % of the Earth’s volume. Most of theEarth’s mass is in the mantle, which is composed of iron(Fe), magnesium (Mg), aluminum (Al), silicon (Si), andoxygen (O) silicate compounds. At over 1000 degrees C,the mantle is solid but can deform slowly in a plasticmanner.

The P waves make abrupt drop in velocity at themantle-core boundary, whereas S wave terminates at themantle-core boundary Thus making a plane ofdiscontinuous surface between the core and the mantleknown as Gutenberg discontinuity.

Based on the behavior of seismic waves, mantle issub-divided into two major parts the upper mantle and thelower mantle.

The upper mantle exists from the base of the crustdownward to a depth of about 670 kilometers. The entire


CONCEPTS OF GEOGRAPHYlayer account for the 83% of volume and 68% of themass of the earth.

This region of the Earth’s interior is thought to becomposed of peridotite, an ultramafic rock made up ofthe minerals olivine and pyroxene.

Asthenosphere: The top layer of the upper mantle,100 to 200 kilometers below surface, is called theasthenosphere. Scientific studies suggest that this layer hasphysical properties that are different from the rest of theupper mantle.

The rocks in this upper portion of the mantle aremore rigid and brittle because of cooler temperatures andlower pressures. Below the upper mantle is the lowermantle that extends from 670 to 2900 kilometers belowthe Earth’s surface. This layer is hot and plastic. The higherpressure in this layer causes the formation of minerals thatare different from those of the upper mantle.

Lithosphere is a layer that includes the crust and theupper most portion of the asthenosphere. This layer isabout 100 kilometers thick and has the ability to glide overthe rest of the upper mantle. Because of increasingtemperature and pressure, deeper portions of thelithosphere are capable of plastic flow over geologic time.The lithosphere is also the zone of earthquakes,mountain building, volcanoes, and continental drift.

CRUST :

The topmost part of the lithosphere consists of crust.This material is cool, rigid, and brittle. The crust isdistinguished from the mantle by the presence of abruptchange in the velocity of seismic waves.

This corresponds to the abrupt change in rigidity ofthe rock from crust to mantle. The change in rigidity inturn is due to change in mineral composition or in physicalstate of the rocks.

The P waves near the surface travel at about 6 kmper second and this velocity increases gradually or abruptlyto the base of the crust, where it is 7 km per second.

The surface of sudden increase in wave velocity, whichseparates the crust above from the mantle below, is theMohorovicic discontinuity, also called Moho discontinuityor M discontinuity. It is named after the Yugoslavseismologist, Mohorovicic, who first recognised thediscontinuity in 1909.

Two types of crust can be identified: continentalcrust. And oceanic crust, both of these types of crustare less dense than the rock found in the underlying uppermantle layer. These layers consist of lighter SIAL(Silica+Aluminium) and denser SIMA(silica=magnesium) respectively. The continental crustis covered by SIAL AND oceanic crust covered bySIMA.

Ocean crust is thin and measures between 5 to 10kilometers thick. It is also composed of basalt and has adensity of about 3.0 grams per cubic centimeter.

The continental crust is 20 to 70 kilometers thickand composed mainly of lighter granite.The density ofcontinental crust is about 2.7 grams per cubic centimeter.It is thinnest in areas like the Rift Valleys of East Africaand in an area known as the Basin and Range Province in thewestern United States.Continental crust is thickest beneathmountain ranges and extends into the mantle. Both of these

crust types are composed of numerous tectonic platesthat float on top of the mantle. Convection currents withinthe mantle cause these plates to move slowly across theAsthenosphere.

Figure: Structure of the Earth’s crust and top mostlayer of the upper mantle. The lithosphere consists of theoceanic crust, continental crust, and uppermost mantle.Beneath the lithosphere is the asthenosphere. This layer,which is also part of the upper mantle, extends to a depthof about 200 kilometers. Sedimentary deposits arecommonly found at the boundaries between the continentaland oceanic crust.

Depth Kilometers Miles

Layer

0–60 0–37 Lithosphere (locally varies

between 5 and 200 km)

0–35 0–22 ... Crust (locally varies between 5 and 70 km)

35–60 22–37 ... Uppermost part of

mantle 35–2890 22–1790 Mantle 100–700 62–435 ... Asthenosphere

2890–5100 1790–3160 Outer core 5100–6378 3160–3954 Inner core


CONCEPTS OF GEOGRAPHYISOSTACY

One interesting property of the continental andoceanic crust is that these tectonic plates have the abilityto rise and sink. This phenomenon, known as isostacy,occurs because the crust floats on top of the mantle like icecubes in water. When large amounts of sediment aredeposited on a particular region, the immense weight ofthe new sediment may cause the crust below to sink.Similarly, when large amounts of material are eroded awayfrom a region, the land may rise to compensate. An analogymay be made with an iceberg - it always floats with acertain proportion of its mass below the surface of thewater. If more ice is added to the top of the iceberg, theiceberg will sink lower in the water. If a layer of ice issomehow sliced off the top of the iceberg, the remainingiceberg will rise. Similarly, the Earth’s lithosphere “floats”in the asthenosphere. In the other words, isostasy is theprinciple observed by Archimedes where he saw that whenan object was immersed, an amount of water equal involume to that of the object was displaced. On a geologicalscale, isostasy can be observed where the Earth’s stronglithosphere exerts stress on the weaker asthenospherewhich, over geological time flows laterally such thatthe load of the lithosphere is accommodated by heightadjustments.

When the Earth’s crust gains weight due to mountainbuilding or glaciation, it deforms and sinks deeper into themantle. If the weight is removed, the crust becomes morebuoyant and floats higher in the mantle.ISOSTASY AND PLATE TECTONICS

When continental plates collide, the continental crustmay thicken at their edges in the collision. If this happens,much of the thickened crust may move downwards ratherthan up as with the iceberg analogy. The idea of continentalcollisions building mountains “up” is therefore rather asimplification. Instead, the crust thickens and the upper partof the thickened crust may become a mountain range.ISOSTASY AND GLACIAL REBOUND

This process explains recent changes in the height ofsea level in coastal areas of eastern and northern Canadaand Scandinavia. Some locations in these regions of the

world have seen sea-level rise by as much as one meterover the last one hundred years. This rise is caused by

isostatic rebound. Both of these areas where covered bymassive glacial ice sheets about 10,000 years ago. Theweight of the ice sheets pushed the crust deeper into themantle. Now that the ice is gone, these areas are slowlyincreasing in height to some new equilibrium level.

Figure : The addition of glacial ice on the Earth’s surfacecauses the crust to deform and sink (a).When the ice melts, isostaticrebound occurs and the crust rises to its former position beforeglaciation (b and c). A similar process occurs with mountain buildingand mountain erosion.

When a certain area of lithosphere reaches the stateof isostasy, it is said to be in isostatic equilibrium. Certainareas (such as the Himalayas) are not in isostaticequilibrium, which has forced researchers to identify otherreasons to explain their topographic heights (in the caseof the Himalaya, by proposing that their elevation is being“propped-up” by the force of the impacting Indian plate).

ROCK SYSTEMSIgneous rocks• Igneous rocks (Granites). Igneous rocks are formed

by the crystallisation of a magma. The differencebetween granites and basalts is in silica content andtheir rates of cooling. A basalt is about 53% SiO2,whereas granite is 73%.o Intrusive, slowly cooled inside the crust. (Plutonic

rock = formed in the earth). Large crystals.• Granite. (Continental crust) Density 2.7-2.8. High

silica content (acidic). = quartz + mica + K-feldsparin solid solution. 60% orthoclase and plagioclasefledspars + 25% quartz + 5% darker minerals (biotite,hornblende). Color from flesh to black. Crystalsintermingled. Hard, rigid, tough. Granitic rock is muchless common on the other terrestrial planets, a facthaving to do with the fractionation (where earlycrystallizing minerals separate fromt he rest of amagma), a process that takes place uniquely on earth,due to the prevalence of plate tectonics.

Granodiorite. An intermediate form betweengranite and diorite.Diorite. High silica content (acidic)Gabbro. Density? Medium silica content.(intermediate). Similar to granite = quartz +feldspar + pyroxene + amphibole + mica +olivene. A layer of gabbro is found in the oceancrust, unerneath the basalt layer (0.5-2.5km), from2.5 to 6.3 km deep. The lunar highlands have manygabbros (made largely of potassium feldspar - alsoknown as plagioclase)Peridotite.

o Extrusive. cooled rapidly at the surface. Small crystals.Rhyolite. Medium silica content (intermediate). Afine-grained volcanic rock of granitic composition.Dacite.


CONCEPTS OF GEOGRAPHYAndesite. (Volcanic arcs) Density >2.8. Low silicacontent (basic) = sodium feldspar + amphibole.Dark, dense.Basalt. (Ocean crust) Density 2.9. Low silicacontent. (basic). Dark, dense. = olivene + pyroxene+ Ca-Feldspar in solid solution. Basaltic rocks(gabbro & basalt) are made up of feldspars andother minerals common in planetary crusts. Theyhave been identified as major surface rocks on thedark lunar planes and much of Mars, Venus andthe asteroid Vesta.

• Pyroclastic rocks: debris ejected by volcanoeso Tuff is made of compacted debris from old

volcanic ash showers.o Volcanic breccia is composed of angular mineral

fragments embedded in a matrix, the product ofexplosive eruptions.

o Ignimbrites are sheets of coalesced fine particleswhich once flowed at high speed, extremely hot,fluid avalanches.

SEDIMENTARY ROCKS• Clastic sedimentary rocks consist of rock and

mineral grains derived from the chemical andmechanical breakdown (weathering) of pre-existingrock. They contain rock fragments and morecommonly, particles of quartz and feldspar. Clasticrocks are further classified on the basis of grain size.Underneath each rock type, the Wentworth Scale ofparticle sizes is shown.o Conglomerates (> 2mm) consolidated gravel

Boulder (>256mm)Cobble (65-256 mm)Pebble (4-64 mm)Granule (2-4 mm)

o Sandstones (0.062-2 mm) consolidated sandVery coarse (1.0 - 2.0 mm)Coarse (0.5 - 1 mm)

Medium (0.25 - 0.5 mm)Fine (0.125 - 0.25 mm)Very fine (0.0625 - 0.125 mm)

o Shales (<0.0062 mm) consolidated mud, rich inorganic matter.

Silt (0.0039 - 0.0625 mm)Clay (0.0002 - 0.0039 mm)Argillite. A sedimentary rock, composed of clayparticles which have been hardened andcemented.Illite (muscovite). K2Al4(Si6Al2)O20(OH)4. isa sedimentary fine-grained rock, equivalent toordinari mica (muscovite).Colloid (<0.0002 mm)

• Chemical sedimentary rocks are formed either fromminerals that precipitate directly from aqeous (water)solutions or from the accumulation of fossilisedremains of organisms which become limestone.

o Gypsum (CaSO4.2H2O)o Anhydrite (CaSO4)o Halite (NaCl) salto Limestone (CaCO3)

Metamorphic rocksMetamorphic rocks have been chemically altered by heat,pressure and deformation, while buried deep in the earth’scrust. These rocks show changes in mineral compositionor texture or both. This area of rock classification is highlyspecialised and complex.• Slates are foliated rocks representing low-grade

metamorphic alteration of shales (laminated clay).o Argillite is a mudstone, much hardened by pressure.• Schists are foliated medium-grade metamorphic rock

with parallel layers, vertical to the direction ofcompaction..

• Gneiss are banded rocks consisting of alternatinglayers of quartz and feldspar, of high metamorphicgrade.

• Quartzites represent metamorphosed sandstone.o Greywacke is a severely hardened sandstone with mica


CONCEPTS OF GEOGRAPHYand feldspar, sometimes containing fossils.

o Chert is a siliceous rock deposited chemically,often common among greywacke.

• Marble is metamorphosed limestone, justrecrystallised.Metamorphic rock may be of sedimentary origin or

stem from igneous rocks. Rocks formed under hightemperatures (basalt, gabbro) are less sensitive tometamorphosis than those solidified at low temperatures(quartz & felspar minerals). The following are causesof metamorphism:• Pressure from sinking deeper while overlaid by

other sediments.• Pressure from continental collision and consequent

folding and overthrusting of the crust (dynamometamorphism).

• Temperature from sinking deeper, into warmerlayers of the crust (metamorphism).

• Temperature from igneous hot lava running nearby,either overhead or from intrusions (contact orthermal metamorphism).

• Temperature from steam escaping from hot vents.• Repetitive metamorphism (polymetamorphism).

IMPORTANT PLAINS OF THE WORLD

In geography, a plain is a large area of land withrelatively low relief. Plains may be more suitable for farmingthan plateaus or mountains. An alluvial plain is a landformformed by the deposition of alluvial soil over a long periodof time by a river coming from the mountains.List of famous plains:

Australian PlainsCanterbury Plains, New ZealandGreat Plains, USAIndo-Gangetic plainKanto plain, JapanNullarbor Plain, AustraliaKhuzestan Plain, IranMazandaran Plain, IranPannonian Plain, Central EuropeSalisbury Plain, EnglandAlexis Leigh Plain, USA

Indo-Gangetic plainThe Indo-Gangetic Plain is a rich, fertile and

ancient land encompassing most of northern and easternIndia, the most populous parts of Pakistan, and virtuallyall of Bangladesh.

It is one of the most populated areas on Earth,home to over 850 million people, more than every othercontinent.The Plains get their names from the riversGanges and Indus.In social and economic terms, theIndo-Gangetic Plain is the most important region ofIndia. The plain is a great alluvial crescent stretchingfrom the Indus River system in Pakistan to the PunjabPlain (in both Pakistan and India) and the Haryana

Plain to the delta of the Ganga (or Ganges) inBangladesh (where it is called the Padma).

Two narrow terrain belts, collectively known asthe Terai, constitute the northern boundary of the Indo-Gangetic Plain. Where the foothills of the Himalayasencounter the plain, small hills known locally as ghar(meaning house in Hindi) have been formed by coarsesands and pebbles deposited by mountain streams.

Groundwater from these areas flows on the surfacewhere the plains begin and converts large areas alongthe rivers into swamps. The southern boundary of theplain begins along the edge of the Great Indian Desertin the state of Rajasthan and continues east along thebase of the hills of the Central Highlands to the Bay ofBengal.

The hills, varying in elevation from 300 to 1,200meters, lie on a general east-west axis.The CentralHighlands are divided into northern and southern parts.The northern part is centered on the Aravalli Range ofeastern Rajasthan. In the northern part of the state ofMadhya Pradesh, the Malwa Plateau comprises thesouthern part of the Central Highlands and merges withthe Vindhya Range to the south. The main rivers thatflow through the southern part of the plain—theNarmada, the Tapti, and the Mahanadi—which delineateNorth India from South India.

The Indo-Gangetic Plain is divided into twodrainage basins by the Delhi Ridge; the western partconsists of the Punjab Plain and the Haryana Plain,and the eastern part consists of the Ganga-Brahmaputradrainage systems.

This divide is only 300 meters above sea level,contributing to the perception that the Indo-GangeticPlain appears to be continuous between the twodrainage basins.

The Punjab Plain is centered in the land betweenfive rivers: the Jhelum, the Chenab, the Ravi, the Beas,and the Sutlej. (The name Punjab comes from theSanskrit pancha ab , meaning five waters or rivers.)

The middle Ganga plain extends from the YamunaRiver in the west to the state of West Bengal in theeast. The lower Ganga and the Assam Valley are morelush and verdant than the middle Ganga.

The lower Ganga is centered in West Bengal fromwhich it flows into Bangladesh and, after joining theJamuna (as the lower reaches of the Brahmaputra areknown in Bangladesh), forms the delta of the Ganga.

The Brahmaputra (meaning son of Brahma) risesin Tibet (China’s Xizang Autonomous Region) as theYarlung Zangbo River, flows through ArunachalPradesh and Assam, and then crosses intoBangladesh.Average annual rainfall increases movingwest to east from approximately 600 millimeters in thePunjab Plain to 1,500 millimeters around the lowerGanga and Brahmaputra. Indo-Gangetic Plain


CONCEPTS OF GEOGRAPHYMOUNTAINS

A mountain is a landform that extends above thesurrounding terrain in a limited area.A mountain isgenerally higher and steeper than a hill, but there isconsiderable overlap, and usage often depends on localcustom.

Mountains cover 54% of Asia, 36% of NorthAmerica, 25% of Europe, 22% of South America, 17%of Australia, and 3% of Africa. As a whole, 24% of theEarth’s land mass is mountainous. Also, 1 in 10 peoplelive in mountainous regions. All the world’s major riversare fed from mountain sources.

Mountains are generally given as heights abovemean sea level. The Himalayas average 5 km above sealevel, whilst the Andes average 4 km. Most othermountain ranges average 2-2.5 km.

The highest mountain on Earth is Everest, 8,848 m,set in the world’s most significant mountain range, theHimalaya.

Other definitions of height are possible. The peak thatis farthest from the center of the Earth is Chimborazoin Ecuador. At 6,267 m above sea level it is not eventhe tallest peak in the Andes, the Earth bulges at theequator and Chimborazo is very close to the equator, itis 2,150 m further away from the Earth’s centre thanEverest.

The peak that rises farthest from its base is MaunaKea on Hawaii, whose peak is over 9,000 m above itsbase on the floor of the Pacific Ocean.Even thoughEverest is the highest mountain on Earth today, therehave been much taller mountains in the past. Duringthe Precambrian era, the Canadian Shield once hadenormous mountains 12,000 m in height that are noweroded down into rolling hills.The tallest knownmountain in the solar system is Olympus Mons, locatedon Mars with 26 km altitude.Characteristics

The altitude of mountains means that the tops existin higher cold layers of the atmosphere. They areconsequently often subject to glaciation and erosion throughfrost action. This produces the classic mountain peak shape.

Some mountains have glacial lakes, created by meltingglaciers; for example, there are an estimated 3,000 inBhutan.

At very high altitudes, there is less oxygen in theair, and less protection against solar radiation (UV).Acute mountain sickness (caused by hypoxia - a lackof oxygen in the blood) affects over half of lowlanderswho spend more than a few hours above 3,500 metres.

Despite some biological adaptation by peopleswho have lived on mountains for hundreds or thousandsof years, babies’ average birthweight is reduced by 100grams for every 1,000-metre gain in altitude. Thus, manystores lining the many mountain ranges known to cause

these sicknesses provide oxygen tanks and higher SPFsunscreens.

GeologyA mountain is usually produced by the movement

of lithospheric plates, either orogenic movement orepeirogenic movement.

The compressional forces, isostatic uplift andintrusion of igneous matter forces surface rock upwards,creating a landform higher than the surrounding features.The height of the feature makes it either a hill or, if higherand steeper, a mountain.

The major mountains tend to occur in long linear arcs,indicating tectonic plate boundaries and activity. Mountaincreation tends to occur in discrete periods, each referredto as an orogeny.

Two types of mountain are formed depending onhow the rock reacts to the tectonic forces – blockmountains or fold mountains.

The compressional forces in continental collisionsmay cause the compressed region to thicken, so theupper surface is forced upwards. In order to balancethe weight, much of the compressed rock is forceddownwards, producing deep “mountain roots”.Mountains therefore form downwards as well asupwards .However, in some continental collisions partof one continent may simply override part of the others,crumpling in the process.

Some isolated mountains were produced byvolcanoes, including many apparently small islands thatreach a great height above the ocean floor.

Block mountains are created when large areas arewidely broken up by faults creating large verticaldisplacements. This occurence is fairly common. Theuplifted blocks are block mountains or horsts. Theintervening dropped blocks are termed graben: these canbe small or form extensive rift valley systems. This formof landscape can be seen in East Africa, the Vosges, theBasin and Range province of Western North Americaand the Rhine valley.

Where rock does not fault it folds, eithersymmetrically or asymmetrically. The upfolds areanticlines and the downfolds are synclines; inasymmetric folding there may also be recumbent andoverturned folds. The Jura mountains are an exampleof folding.

GrasslandsSavanna

A savana or savannah is a grassland with widelyspaced trees, and occurs in several types of biomes.

In savannas, grasses and trees are co-dominantvegetation types, with trees and grasses often alternatingin dominance over time. The herbaceous layer is usuallya mixture of grasses and herbs with trees and shrubsscattered individually or in small clumps.


CONCEPTS OF GEOGRAPHYSavannas are frequently seen as a transitional zone,

occurring between forest or woodland regions andgrassland or desert regions.

Savannas are targets of regular fires. Most savannasexperience fire at least twice a decade and annual fires arecommon in many savanna types. These fires are usuallyconfined to the herbaceous layer and do little long termdamage to mature trees.

However these fires do serve to either kill or suppresstree seedlings, thus preventing the establishment of acontinuous tree canopy which would prevent further grassgrowth. Browsing animals such as elephants, antelope anddeer also play an important role in supressing tree growthin savannas.

Savannas appear to be the result of human use offire. For example Native Americans created subtropicalsavannas by periodic burning in some areas of the USsoutheastern coast where fire-resistant Longleaf Pine wasthe dominant species.

Aboriginal burning appears to have been responsiblefor the widespread occurance of savanna in tropicalAustralia and New Guinea and savannas in India are acreation of human fire use .With the removal or laterationof traditional burning regimes many savannas are beingreplaced by forest and shrub thickets with little herbaceouslayer.

Although the term savanna is believed to haveoriginally come from an Amerindian word describing “landwhich is without trees but with much grass either tall orshort” (Oviedo y Valdes, 1535), by the late 1800s it wasused to mean “land with both grass and trees”. It nowrefers to land with grass and either scattered trees, or anopen canopy of trees. Savannah, Georgia is named aftersuch an area.Savanna ecoregions are of several different types:

Tropical and subtropical savannas are classifiedwith tropical and subtropical grasslands and shrublandsas the tropical and subtropical grasslands, savannas, andshrublands biome. The savannas of Africa, including theSerengeti, famous for its wildlife, are typical of this type.

Temperate savannas are mid-latitude savannas withwetter summers and drier winters. They are classified withtemperate savannas and shrublands as the temperategrasslands, savannas, and shrublands biome.

Mediterranean savannas are mid-latitude savannas inMediterranean climate regions, with mild, rainy winters andhot, dry summers, part of the Mediterranean forests,woodlands, and shrub biome. The oak tree savannas ofCalifornia, part of the California chaparral andwoodlands ecoregion, fall into this category.

Flooded savannas are savannas that are floodedseasonally or year-round. They are classified withflooded savannas as the flooded grasslands and savannasbiome, which occurs mostly in the tropics andsubtropics.

Montane savannas are high-altitude savannas,located in a few spots around the world’s high mountainregions, part of the montane grasslands and shrublandsbiome. The highland savannas of the Angolan scarpsavanna and woodlands ecoregion are an example.Steppe

In physical geography, a steppe pronounced inEnglish as step, is a plain without trees (apart fromthose near rivers and lakes);

It is similar to a prairie, although a prairie isgenerally considered as being dominated by tall grasses,while short grasses are said to be the norm in the steppe.It may be semi-desert, or covered with grass or shrubs,or both depending on the season and latitude.

The term is also used to denote the climateencountered in regions too dry to support a forest, butnot dry enough to be a desert.

The soil is considered too moist to be a desert, buttoo dry to support normal forest life. The climate of mid-latitude steppes can be summarized by hot summers andcold winters, averaging 250-500 mm (10-20 inches) of rainor equivalent in snowfall per year.

In tropical locations, necessary rainfall to separatesteppes from true deserts may be as half again as muchdue to greater evapotranspiration.

Plant life is usually greater than one foot tall, includingthe blue grama and buffalo grass, cacti, sagebrush,speargrass, and other small relatives of the sunflower.

Animal life includes the Corsac Fox, Mongolian Gerbil,Saiga Antelope, Northern Lynx, and the Saker Falcon.

The world’s largest zone of steppes, often referred toas “the Great Steppe”, is found in central Russia andneighbouring countries in Central Asia. The Pontic steppestretches from the Ukraine in the west to the UralMountains and the Caspian Sea. To the east of theCaspian Sea, the steppes extend through Turkmenistan,Uzbekistan and Kazakhstan to the Altai, Koppet Dagand Tian Shan ranges. To the north, on the eastern sideof the Urals, is the forested West Siberian Plain taiga,extending nearly as far as the Arctic Ocean.

Other regions of steppes include transition zonesbetween savanna and severe desert such as the Sahel thatfringes the true Sahara or similar semi-arid lands that fringethe Thar desert of the Indian subcontinent or the moresevere deserts of Australia.

Another large steppe area is located in the centralUnited States and western Canada. The High Plains steppeis the westernmost part of the Great Plains region. Asignificant steppe, noteworthy for not grading intodesert, is the Sertão of northeastern Brazil.

Some steppes are to be found in transition zonesbetween zones of Mediterranean climate and desert,such as Tijuana, Baja California, and in places cut offfrom adequate moisture due to rainshadow effects suchas Zaragoza, Spain.


CONCEPTS OF GEOGRAPHYPrairie

Prairie refers to an area of land of low topographicrelief that historically supported grasses and herbs, withfew trees, and having generally a mesic (moderate ortemperate) climate.

Lands typically referred to as “prairie” tend to be inNorth America. The term encompassed much of the areareferred to as the Great Plains (constituted by most or allof the states of North Dakota, South Dakota, Nebraska,Kansas, Oklahoma, Texas, Colorado, Wyoming andMontana), and sizeable parts of the states of Indiana,Illinois, Iowa, Missouri, Wisconsin and Minnesota. InCanada, prairie occupied vast areas of Manitoba,Saskatchewan, and Alberta.

French explorers called these areas pririe, from theFrench word for “meadow” (or)Medium grass areas.The shortgrass area can be considered to be a steppe.

Grazing by animals such as the American Bisonand Prairie dogs also helped maintain the originalprairie ecology. Small areas of prairies also exist ineastern North America, and it is possible that thesewere created by Native Americans by periodic burning.One such area was along the southeastern shore of LakeErie in what is now Pennsylvania and New York;another was between Seneca Lake and Cayuga Lake inpresent New York.

Prairies are considered part of the temperategrasslands, savannas, and shrublands biome by ecologists,based on similar temperate climates, moderate rainfall, andgrasses, herbs, and shrubs, rather than trees, as thedominant vegetation type. Other temperate grasslandsregions include the Pampas of Argentina, and thesteppes of Russia and Ukraine.

VeldThe term Veld, or Veldt, refers primarily (but not

exclusively) to the wide open rural spaces of SouthAfrica or southern Africa and in particular to certainflatter areas or districts covered in grass or low scrub.

The word comes from the Afrikaans and Dutchlanguages, and is also found in some dialects of LowGerman and means, literally, ‘field’ The term ‘veld’, in LowGerman usage, is used to mean a place which isgenerally overgrown or has gone fallow, such as athicket or a field which has become overgrown fromlack of maintenance. It also generally has similarconnotations as in Afrikaans and Dutch.

By extension, the veld can be compared to ‘theboondocks’ or those places ‘beyond the black stump’ inAustralia.Highveld and Lowveld

Much of the interior of southern Africa consists ofa high plateau known as the Highveld. These higher, coolerareas (generally more than 5000 ft [1524m] above sea level)are characterized by flat or gently undulating terrain,

grasslands and a modified tropical or subtropicalclimate. In some areas there is a distinct escarpmentbordering the plateau, while in others the boundary isnot obvious.

Some surrounding, lower areas are known aslowveld and are generally hotter and less intensivelycultivated. Before the middle of the 20th century muchof the Lowveld was home to the Tse Tse Fly, whichtransmits Sleeping Sickness. These areas used to beknown as ‘fever country’ and were avoided by mountedtravellers, owing to the susceptibility of horses to a formof the disease.

Coastal plainIn geography, a coastal plain is an area of flat, low-

lying land adjacent to a seacoast and separated from theinterior by other features.

One of the world’s longest coastal plains is locatedin western South America. The southeastern coastalplain of North America is notable for its speciesdiversity. The coastal plain of North America extendsnorthwards from the Gulf of Mexico along the LowerMississippi River to the Ohio River, which is a distanceof about 500 miles (about 800 km).Some well-known coastal plainsThe Illawarra Plains, Australia, The Israeli CoastalPlain, The Atlantic Coastal Plain, United States

Ridge :A ridge is a geological feature that features a

continuous elevational crest for some distance. Ridgesare usually termed hills or mountains as well, dependingon size. There are several main types of ridges:

Dendritic ridge: In a typical plateau terrain, thestream drainage valleys will leave intervening ridges.These are by far the most common ridges. These ridgesusually represent slightly harder rock, but not always— they are often simply because there were larger jointspaces where the valleys formed, or other chanceoccurrences. This type of ridge is generally somewhatrandom in orientation, often changing directionfrequently, often with knobs at intervals on the ridgetop.

Stratigraphic ridge: In places such as the Ridge-and-valley Appalachians, very long, very even, verystraight ridges are formed due to the fact that they’rethe uneroded remaining edges of the more resistantstrata that were folded laterally. Similar ridges haveformed in places such as the Black Hills, where theridges form concentric circles around the igneous core.Sometimes these ridges are called “hogback ridges”.

Oceanic spreading ridge: In tectonic spreadingzones around the world, such as at the Mid-AtlanticRidge, the volcanic activity forming new plate boundaryforms volcanic ridges at the spreading zone. Isostatic


CONCEPTS OF GEOGRAPHYsettling and erosion gradually reduce the elevationsmoving away from the zone.

Crater ridges: Large meteorite strikes typically formlarge impact craters bordered by circular ridges.

Volcanic caldera ridges: Large volcanoes often leavecollapsed central calderas that are bordered by circularridges.

Thrust fault ridges: Thrust faults often formescarpments. Sometimes the tops of the escarpments formnot plateaus, but slope back so that the edges of theescarpments form ridges.

Dune ridges: In areas of large-scale dune activity,certain types of dunes result in sand ridges.

Moraines and eskers: Glacial activity may leave ridgesin the form of moraines and eskers. An arête is a thinridge of rock that is formed by glaciers.Valley

A valley (in Scotland, a glen) is a landform, whichcan range from a few square miles (square kilometers)to hundreds or even thousands of square miles in area.

It is typically a low-lying area of land, surroundedby higher areas such as mountains or hills. It can alsobe seen as a path between two mountains, or adepression in a single mountain.

Valleys are formed by numerous geographicalprocesses. Glacial valleys, which are usually U- rather thanV-shaped, were formed tens of thousands of years ago(most likely during the last Ice Age) by the massive erosivepower of glaciers.

Several glacial valleys can be found in the EnglishLake District and many can be found in Alpinecountries. Rift valleys, such as the Great Rift Valley,are formed by the expansion of the Earth’s crust due totectonic activity beneath the Earth’s surface.

Valleys are, however, most commonly formed byfluvial activity (the action of running water, such as rivers),which erodes the landscape

Usually the bottom of a main valley is broad -independent of the U or V shape.

It ranges from about 1 to 5 km and is filled withmountain sediments. The shape of the floor can be ratherhorizontal, similar to a flat cylinder, or terraced. Side valleysare rather V than U-shaped;

Predominant are places on terraces or Alluvial fans ifthey exist.

The villages of the primary valleys, however, haveto consider mainly the danger of possible floodings.Hollows :

A hollow is loose name for a valley in the earth. Itis commonly used in New England, Missouri andwestern Pennsylvania to describe such geographicfeatures. Hollows may be formed by river valleys suchas Mansfield Hollow or they may be relatively dry

clefts with a notch-like characteristic in that they havea height of land and consequent water divide in theirbases.

A hollow such as this is Boston Hollow. Touristsin Europe can further visit a lot of Karst, Stalactite andIce Hollows (e.g. in Slovenia and Austria).

Famous valleys California Central Valley (UnitedStates), Copper Canyon, Danube Valley (Eastern Europe,Wachau, Iron Gate), Death Valley (United States), GrandCanyon (United States), Great Rift Valley (from Jordan tothe Red Sea and Lake Victoria), Indus Valley (Pakistan),Loire Valley with its famous castles (France), Napa Valley(United States), Upper Rhine Valley (an old graben system)(France), Rhone Valley from the Matterhorn to Grenobleand Lyon (France), Shenandoah Valley (United States),Sonoma Valley, California, USA, Valley of the Kings(Egypt), San Fernando Valley (United States), Santa ClaraValley, perhaps better known as “Silicon Valley” (UnitedStates).

The largest valley in our solar system is the VallesMarineris formation on Mars. The Valles (which werefirst detected in 1877 by Schiaparelli) are a huge canyonsystem, 4,500 x 600 km in area and up to 8 km in depth.These enormous dimensions are 4-8 times greater thanthose of the American “Grand Canyon”.River delta :

A delta is a landform where the mouth of a riverflows into an ocean, sea, desert, estuary or lake, buildingoutwards (as a deltaic deposit) from sediment carried bythe river and deposited as the water current is dissipated.

Deltaic deposits of larger, heavily-laden rivers arecharacterized by the river channel dividing into multiplestreams (distributaries), these divide and come togetheragain to form a maze of active and inactive channels. Arelated notion is estuaries, which are another type of rivermouth.

A deposit at the mouth of a river usually roughlytriangular in shape. The triangular shape and the increasedwidth at the base are due to blocking of the river mouthby silt, with resulting continual formation of distributariesat angles to the original course.

Herodotus the great historian used this term forthe Nile river delta because the sediment deposit at itsmouth had the shape of upper-case Greek letter Delta:Ä.

Where delta formation is river-dominated and lesssubject to tidal or wave action, a delta may take on amulti-lobed shape which resembles a bird’s foot. TheMississippi Delta is an example of this type.

The most famous delta is that of the Nile River,and it is this delta from which the term is derived,because the Nile delta has a very characteristictriangular shape, like the (upper-case) Greek letter delta(Ä).

Other rivers with notable deltas include the


CONCEPTS OF GEOGRAPHYAmazon, the Ganges/Brahmaputra combination (thisdelta spans most of Bangladesh and West Bengal), theNiger, the Mississippi, the Sacramento-San Joaquin, theRhine, the Rhône, the Danube, the Ebro, the Volga, theLena, the Tigris-Euphrates, the Indus, the Krishna-Godavari, the Kaveri, the Ayeyarwady, and the Mekong.

In rare cases the river delta is located inside a largevalley and is called an inverted river delta. Sometimes ariver will divide into multiple branches in an inland area,only to rejoin and continue to the sea; such an area isknown as an inland delta, and often occur on former lakebeds. The Niger Inland Delta is the most notableexample. These rock formations, which sometimescontain coal, cap the thick series of sedimentary rocksof the Allegheny Plateau in eastern North America.List of deltas

Camargue (Rhône River Delta), Colorado RiverDelta, Danube Delta, Ganges-Brahmaputra Delta, IndusRiver Delta, Lena Delta, Mekong Delta, MississippiRiver Delta, Niger Inland Delta (inland delta), NigerRiver Delta (Oil Rivers), Nile Delta, Okavango Delta(inland delta), Paraná Delta, Pearl River Delta, RioGrande Valley, Rhine-Meuse-Scheldt Delta, SacramentoRiver Delta, Volga Delta, Yangtze River Delta, YukonDelta.Oxbow lake

An oxbow lake is a type of lake which is formedwhen a wide meander from a stream or a river is cutoff to form a lake. They are called oxbow lakes due tothe distinctive curved shape that results from thisprocess. In Australia, an oxbow lake is called abillabong.

When a river reaches a low-lying plain in its finalcourse to the sea or a lake, it meanders widely.Deposition occurs on the convex bank because of the‘slack water’, or water at low velocity. In contrast, bothlateral erosion and undercutting occur on the concavebank where the stream’s velocity is the highest.Continuous erosion of a concave bank and depositionon the convex bank of a meandering river cause theformation of a very pronounced meander with twoconcave banks getting closer. The narrow neck of landbetween the two neighbouring concave banks is finallycut through, either by lateral erosion of the two concavebanks or by the strong currents of a flood. When thishappens, a new straighter river channel is created andan abandoned meander loop, called a cut-off, is formed.When deposition finally seals off the cut-off from theriver channel, an oxbow lake is formed.

ExamplesThe Reelfoot Lake in west Tennessee is an oxbow

lake formed when the Mississippi River changed coursefollowing the New Madrid Earthquake of 1811–1812.There are many oxbow lakes alongside the MississippiRiver and its tributaries. The largest oxbow lake in

North America, Lake Chicot (located near Lake Village,Arkansas), was originally part of the Arkansas River.

Cuckmere Haven in Sussex, England contains awidely meandering river with many oxbow lakes, oftenreferred to in physical geography textbooks.

River :A river is a large natural waterway. The source of

a river may be a lake, a spring, or a collection of smallstreams, known as headwaters.

From their source, all rivers flow downhill, typicallyterminating in the ocean. The mouth, or lower end, of ariver is known as its base level.

Rivers that carry large amounts of sediment developconspicuous deltas at their mouths. Rivers whose mouthsare in saline tidal waters may form estuaries.There are different stages of river course.

Youthful river - a river with a steep gradient thathas very few tributaries and flows quickly. Its channelserode deeper rather than wider.

Mature river - a river with a gradient that is lesssteep than those of youthful rivers and flows moreslowly than youthful rivers. A mature river is fed bymany tributaries and has more discharge than a youthfulriver. Its channels erode wider rather than deeper.

Old river - a river with a low gradient and lowerosive energy. Old rivers are characterized by floodplains.

Rejuvenated river - a river with a gradient that israised by the earth’s movement.

Where a river descends quickly over slopedtopography,as rapids with whitewater or even waterfallsoccur. Rapids are often used for recreational purposes.

Rivers begin at their source in higher ground, eitherrising from a spring, forming from glacial meltwater, flowingfrom a body of water such as a lake, or simply from damp,boggy places where the soil is waterlogged.

They end at their base level where they flow into alarger body of water, the sea, a lake, or as a tributaryto another (usually larger) river.

In arid areas rivers sometimes end by losing waterto evaporation and percolation into dry, porous materialsuch as sand, soil, or pervious rock. The area drainedby a river and its tributaries is called its watershed,catchment basin or drainage basin. (Watershed is alsoused however to mean a boundary between drainagebasins.)

Starting at the mouth of the river and following itupstream as it branches again and again, the resultingriver network forms a dendritic (tree-like) structure.

Rivers have been important historically indetermining political boundaries. For example, theDanube was a longstanding border of the RomanEmpire, and today forms most of the border between


CONCEPTS OF GEOGRAPHYBulgaria and Romania.

The Mississippi in North America, and the Rhinein Europe, are major east-west boundaries in thosecontinents. The Orange River forms the boundarybetween various provinces and countries along its routein Africa.The world’s ten longest rivers

It is difficult to measure the length of a river, themore precise the measurement, the longer the river willseem. Also, it is difficult to determine where a river beginsor ends, as very often, upstream rivers are formed byseasonal streams, swamps, or changing lakes.These are average measurements.

Nile (6,690 km), Amazon (6,452 km), Mississippi-Missouri (6,270 km), Yangtze (Chang Jiang) (6,245 km),Yenisey-Angara (5,550 km), Huang He (Yellow) (5,464 km),Ob-Irtysh (5,410 km), Amur (4,410 km), Congo (4,380 km),Lena (4,260 km).Well-known rivers (in alphabetic order)1. The Amazon River, the largest river in the world (in

terms of volume and water cubic metres/second)2. The American River, the site of Sutter’s Mill3 Amu Darya, the longest river in central Asia4. The Amur, the principal river of eastern Siberia and

the border between Russia and China5. The Arkansas River, a major tributary of the Mississippi

River6. The Arno, the river that runs through Florence7. The Arvandrud (Shatt al-Arab), the river that borders

Iran and Iraq8. The Brahmaputra, the principal river in northeast India

and Tibet9. The Chao Phraya, the principal river of Thailand10. The River Clyde, which runs through Glasgow11. The Colorado River (in Argentina)12. The Colorado River (in the United States), the principal

river of the American Southwest13. The Columbia River, the principal river of the Pacific

Northwest14. The Congo, the principal river of central Africa15. The Danube, the principal river of central and

southeastern Europe16. Río de la Plata, the widest river in the world17. The Ebro, a river in northwestern Spain18. The Elbe, a major German river, running through

the city of Hamburg19. The Euphrates, one of the twin principal rivers of

Anatolia (Turkey) and Mesopotamia (Iraq)20. The Ganga, the principal river of India21. Han-gang, the river that runs through Seoul22. The Helmand River, the principal river of Afghanistan

23. The Huang He (or Yellow River), one of the principalrivers of China

24. The Hudson River, the principal river of New York25. The Indus River, the principal river of Pakistan26. The River Jordan, the principal river of Israel Karun,

the principal navigable river of southern Iran27. The River Kaveri, the principal river of South India28. The Lena, the principal river of northeastern Siberia29. The Mackenzie River, the longest river in Canada30. The Magdalena, the principal river of Colombia31. The Main, a river in Germany32. The Mekong, a principal river of Southeast Asia33. The River Mersey, the river on which sits the

English city of Liverpool34. The Maas, the principal river of the southern

provinces of the Netherlands and eastern Belgium35. The Mississippi River, the principal river of the

central and southern United States The MissouriRiver, one of the principal rivers of the Great Plains

36. The Murray River, the principal river ofsoutheastern Australia

37. The Niagara River, the river which flows betweenLake Erie and Lake Ontario, and which flows overthe Niagara Escarpment (better known as NiagaraFalls)

38. The Niger, the principal river of west Africa39. The Nile, the longest river in the world, principal

to Egypt and northeastern Africa40. The Ob, a large river of Siberia41. The Oder, a major river in Central Europe42. The Ohio River, the largest river between the

Mississippi and the Appalachian Mountains43. The Orinoco, the principal river of Venezuela The Rio

Grande, the river that forms part of the borderbetween the United States and Mexico

44. The Saint Lawrence River, which drains the GreatLakes

45. The Sava, which flows through four countries—Slovenia, Croatia, Bosnia and Herzegovina(makingits northern border) and Serbia—and was thereforeone of the symbols of former Yugoslavia

46. The Savannah River, a major river in thesoutheastern United States, forming most of theborder between the states of Georgia and SouthCarolina

47. The Seine, the river that runs through Paris48. The Segura, a river in southeastern Spain49. The River Severn, the longest river in Great Britain50. Shinano-gawa, the longest river in Japan51. The Snake River, the largest tributary of the

Columbia River in Washington


CONCEPTS OF GEOGRAPHY52. The Susquehanna River, the principal river of

Pennsylvania and the Chesapeake Bay53. Tajo, the largest river in the Iberian Peninsula54. The River Tay, the largest river in Scotland55. The Tennessee River, an important tributary of the

Mississippi that flows through Eastern/WesternTennessee, Northern Alabama, and Kentucky

56. The Thames, the river that runs through London57. The Tiber, the river that runs through Rome58. The Tigris, one of the twin principal rivers of Anatolia

(Turkey) and Mesopotamia (Iraq)59. Tonegawa, one of the largest rivers in Japan60. The Vistula, the principal river of Poland61. The Vltava, the river that runs through Prague62. The Volga River, the principal river of Russia63. The Wabash River, the principal river of Indiana64. The Yangtze (Chang Jiang), the longest river in

China65. The Yenisei, a large river in Siberia66. The Yukon, the principal river of Alaska and the

Yukon Territory67. The Zambezi, the principal river of southeastern

Africa

The 16 current Decade Volcanoes• Avachinsky-Koryaksky, Kamchatka, Russia• Colima, Mexico• Mount Etna, Italy• Galeras, Colombia• Mauna Loa, Hawai»i, USA• Merapi, Indonesia• Nyiragongo, Democratic Republic of the Congo• Mount Rainier, Washington, USA• Sakurajima, Japan• Santamaria/Santiaguito, Guatemala• Santorini, Greece• Taal Volcano, Philippines• Teide, Canary Islands, Spain• Ulawun, Papua New Guinea• Mount Unzen, Japan• Vesuvius, Italy

Effect of VolcanoesLarge, explosive volcanic eruptions inject water

vapor (H2O), carbon dioxide (CO2), sulfur dioxide (SO2),hydrogen chloride (HCl), hydrogen fluoride (HF) andash (pulverized rock and pumice) into the stratosphereto heights of 10-20 miles above the Earth’s surface.

The most significant impacts from these injectionscome from the conversion of sulphur dioxide tosulphuric acid (H2SO4), which condenses rapidly in thestratosphere to form fine sulfate aerosols.

The aerosols increase the Earth’s albedo—its

reflection of radiation from the Sun back into space -and thus cool the Earth’s lower atmosphere ortroposphere; however, they also absorb heat radiatedup from the Earth, thereby warming the stratosphere.

Several eruptions during the past century havecaused a decline in the average temperature at theEarth’s surface of up to half a degree (Fahrenheit scale)for periods of one to three years. The sulphate aerosolsalso promote complex chemical reactions on theirsurfaces that alter chlorine and nitrogen chemical speciesin the stratosphere. This effect, together with increasedstratospheric chlorine levels from chlorofluorocarbonpollution, generates chlorine monoxide (ClO), whichdestroys ozone (O3).

As the aerosols grow and coagulate, they settledown into the upper troposphere where they serve asnuclei for cirrus clouds and further modify the Earth’sradiation balance. Most of the hydrogen chloride (HCl)and hydrogen fluoride (HF) are dissolved in waterdroplets in the eruption cloud and quickly fall to theground as acid rain.

Gas emissions from volcanoes are a naturalcontributor to acid rain. Volcanic activity releases about130 to 230 teragrams (145 million to 255 million shorttons) of carbon dioxide each year.Pacific Ring of Fire

The Pacific Ring of Fire is a zone of frequentearthquakes and volcanic eruptions encircling the basin ofthe Pacific Ocean. In a 40,000 km horseshoe shape, it isassociated with a nearly continuous series of oceanictrenches, island arcs, and volcanic mountain ranges and/or plate movements. It is sometimes called the circum-Pacific belt or the circum-Pacific seismic belt.

90% of the world’s earthquakes and 81% of theworld’s largest earthquakes occur along the Ring of Fire.The next most seismic region (5–6% of earthquakes and17% of the world’s largest earthquakes) is the Alpidebelt which extends from Java to Sumatra through theHimalayas, the Mediterranean, and out into the Atlantic.

The Mid-Atlantic Ridge is the third mostprominent earthquake belt.Countries of the Pacific Ring of Fire

• Argentina • Belize • Bolivia • Brazil • Brunei •Canada • Colombia • Chile • Costa Rica • Ecuador •East Timor • El Salvador • Micronesia • Fiji • Guatemala• Honduras • Indonesia • Japan • Kiribati • Malaysia •Mexico • New Zealand • Nicaragua • Palau •Papua New Guinea • Panama • Peru • Philippines •Russia • Samoa • Solomon Islands • Tonga • Tuvalu •United States •Volcanoes of the Pacific Ring of Fire

• Mount Baker • Mount Bulusan •Cold Bay Volcano • Concepción • Volcán de Fuego •Mount Fuji • Galeras • Mount Hood • Krakatoa •Mayon Volcano • Mount Merapi • Momotombo •


CONCEPTS OF GEOGRAPHYNovarupta • Paricutín • Pico de Orizaba •Mount Pinatubo • Popocatépetl • Mount Shasta •Mount Rainier • Mount Ruapehu • Nevado del Ruiz •Mount St. Helens • Mount Tambora • Mount Taranaki• Tungurahua • Mount Usu •

DESERT :In geography, a desert is a landscape form or region

that receives very little precipitation. The English,French (désert), Italian (deserto), all come from the Latindeserta. This name is derived from the old Egyptianlanguage, from the word deshert, meaning the ‘red land’that bordered the black land (kemet) in the nile valleyfrom the east and the west.

Generally deserts are defined as areas that receivean average annual precipitation of less than 250 mm(10 inches).

Desert is a vague term, the use of ‘dryland’, andits subdivisions of hyper arid, arid, semiarid and dry-subhumid, is to be preferred, and is approved by theUnited Nations.

Deserts cover at least one-fifth of the Earth’s landsurface. Deserts are very arid (dry) and can have hightemperatures in excess of 50°C. Even though the desertis very hot in the day, it is extremely cold at night.

Sand dunes called ergs and stony surfaces calledReg or hamada surfaces compose a minority of desertsurfaces. Exposures of rocky terrain are typical, andreflect minimal soil development and sparseness ofvegetation. Bottom lands may be salt-covered flats.

Eolian (wind-driven) processes are major factorsin shaping desert landscapes. Cold deserts (also knownas polar deserts) have similar features but the main formof precipation is snow rather than rain.

The largest cold desert is Antarctica (composedof about 98 percent thick continental ice sheet and 2percent barren rock). The largest hot desert is theSahara.

Types of desertMost classifications rely on some combination of

the number of days of rainfall, the total amount ofannual rainfall, temperature, humidity, or other factors.

However, lack of rainfall alone can’t provide anaccurate description of what a desert is. For example,Phoenix, Arizona receives less than 250 millimeters (10inches) of precipitation per year, and is immediatelyrecognized as being located in a desert.

The North Slope of Alaska’s Brooks Range alsoreceives less than 250 millimeters of precipitation per year,but is not generally recognized as a desert region.

Cold deserts can be covered in snow; such locationsdon’t receive much precipitation, and what does fallremains frozen as snow pack; these are more commonlyreferred to as tundra if a short season of above-freezingtemperatures is experienced, or as an ice cap if the

temperature remains below freezing year-round,rendering the land almost completely lifeless.Montane deserts

Montane deserts are arid places with a very highaltitude; the most prominent example is found north ofthe Himalaya, in parts of the Kunlun Mountains andthe Tibetan Plateau. Many locations within this categoryhave elevations exceeding 3,000 meters (9,843 feet) andthe thermal regime can be hemiboreal. These placesowe their profound aridity (the average annualprecipitation is often less than 40mm) to being very farfrom the nearest available sources of moisture. Desertsare normally cold.Desert features

Sand covers only about 20 percent of Earth’sdeserts. Most of the sand is in sand sheets and sandseas—vast regions of undulating dunes resembling oceanwaves “frozen” in an instant of time. In general, thereare 6 forms of deserts:

Mountain and basin deserts;Hamada deserts, which comprise of plateaux

landforms;Regs which consist of rock pavements;Ergs which are formed by sand seas;Intermontane Basins; andBadlands which are located at the margins of arid

lands comprising of clay-rich soil.Nearly all desert surfaces are plains where eolian

deflation—removal of fine-grained material by thewind—has exposed loose gravels consistingpredominantly of pebbles but with occasional cobbles.

The remaining surfaces of arid lands are composedof exposed bedrock outcrops, desert soils, and fluvialdeposits including alluvial fans, playas, desert lakes, andoases. Bedrock outcrops commonly occur as smallmountains surrounded by extensive erosional plains.

There are several different types of dunes. Barchandunes are produced by strong winds blowing across alevel surface and are crescent-shaped. Longitudinal orseif dunes are dunes that are parallel to a strong windthat blows in one general direction. Transverse dunesrun at a right angle to the constant wind direction. Stardunes are star-shaped and have several ridges that spreadout around a point.

Oases are vegetated areas moistened by springs,wells, or by irrigation. Many are artificial. Oases areoften the only places in deserts that support crops andpermanent habitation.Vegetation

Most desert plants are drought- or salt-tolerant, suchas xerophytes.Some store water in their leaves, roots,and stems. Other desert plants have long tap roots thatpenetrate to the water table if present. The stems and


CONCEPTS OF GEOGRAPHYleaves of some plants lower the surface velocity of sand-carrying winds and protect the ground from erosion.

Deserts typically have a plant cover that is sparsebut enormously diverse. The Sonoran Desert of theAmerican Southwest has the most complex desertvegetation on Earth. The giant saguaro cacti providenests for desert birds and serve as “trees” of the desert.

Although cacti are often thought of as characteristicdesert plants, other types of plants have adapted wellto the arid environment. They include the pea andsunflower families. Cold deserts have grasses and shrubsas dominant vegetation.LIST OF DESERTSAfrica :1. Sahara – in northern Africa. The world’s largest

desert after Antarctica.2. Kalahari – desert in southern Africa.3. Namib – desert in southern Africa.Antarctica :

Antarctica The interior of the continent is theworld’s largest desert.Asia :

Gobi – desert of Mongolia, Taklamakan – desert inChina, Ordos – desert of China, Kara Kum – deserts inCentral Asia, Kyzyl Kum – Kazakhstan and Uzbekistan,Thar-Cholistan desert in India and Pakistan.Australia :

Gibson Desert – central Australia, Great Sandy Desert– northwestern Australia, Great Victoria Desert – centralAustralia, Simpson Desert – central Australia, LittleSandy Desert – central Australia, Strzelecki Desert –southcentral Australia, Tanami Desert – northernAustralia, Western Desert – western Australia.Europe :

Hálendi – Iceland Europes largest desert.Bledowska Desert – Lesser Poland Voivodeship,

PolandMiddle East:

Arabian Desert — a vast desert complex onArabian Peninsula comprising Al-Dahna Desert, EmptyQuarter, Nefud Desert and other deserts.

Dasht-e Kavir – central Iran.Dasht-e Lut – southeastern Iran.Judean Desert – eastern Israel and West Bank.Negev – southern Israel

Desert of Sin / Zin Desert (Bible usage) – SinaiPeninsula.North America:

Mojave desert, Great Basin desert, Sonoran desert,Chihuahuan desert.South America:

La Guajira Desert – in northern Colombia and someof northwestern Venezuela.

Atacama – desert in Chile. The driest desert onEarth.List of deserts by area :

This is a list of deserts in the world ordered byarea. It includes all deserts with an area greater than 50000 km² (19 300 square miles).Deserts over 50 000 km² :Rank Desert’s Name Country/Countries1 Antarctic Desert N/A2 Sahara Desert Egypt, Libya, Chad,

Mauritania, Morocco, Algeria.3 Arabian Desert Saudi Arabia, Jordan, Iraq,

Kuwait, Qatar, United ArabEmirates, Oman and Yemen.

4 Gobi Desert Mongolia5 Patagonian Desert Argentina6 Great Victoria Desert Australia7 Great Bassin Desert United States8 Chihuahuan Desert Mexico and United States9 Great Sandy Desert Australia10 Kara-Kum Desert Turkmenistan11 Sonoran Desert United States and Mexico12 Kyzyl Kum Kazakhstan and Uzbekistan13 Taklamakan or

Takla Makan Desert People’s Republic of China14 Kalahari Desert Botswana, Namibia and

South Africa14 Kavir or Dasht-e

Kavir Desert Iran14 Syrian Desert Syria, Jordan and Iraq15 Thar or Great

Indian Desert India and Pakistan16 Gibson Desert Australia17 Simpson Desert Australia18 Atacama Desert Chile19 Namib Desert Namibia20 Mojave Desert United States

SeaA sea is a large expanse of saline water connected

with an ocean, or a large, usually saline, lake that lacks anatural outlet such as the Caspian Sea and the DeadSea. The term is used colloquially as synonymous withocean, as in the tropical sea or down to the sea shore,or even sea water referring to water of the ocean. Largelakes are sometimes referred to as inland seas, such asthe Great Lakes. Many seas are marginal seas, in whichcurrents are caused by ocean winds; others aremediterranean seas, in which currents are caused bydifferences in salinity and temperature.

The International Hydrographic Organization(IHO) is the world authority when it comes to definingseas. The current defining document is the Specialpublication S-23, Limits of Oceans and Seas, 3rd edition,


CONCEPTS OF GEOGRAPHY1953. The second edition dated back to 1937, and thefirst to 1928. A fourth edition draft was published in1986 but so far several naming disputes (such as theone over the Sea of Japan) have prevented itsratification.LIST OF SEASAtlantic Ocean

Mediterranean Sea on the coast of Antalya, Turkeyat sunset, Baffin Bay, Gulf of St. Lawrence, Bay ofFundy, Caribbean Sea, Gulf of Mexico, Sargasso Sea,North Sea, Baltic Sea, Central Baltic Sea, Gulf of Bothnia,Bay of Bothnia, Bothnian Sea, Gulf of Finland, Sea ofthe Hebrides , Irish Sea, Celtic Sea, Mediterranean Sea,Adriatic Sea, Aegean Sea, Mirtoon Sea, Sea of Crete,Thracian Sea, Alboran Sea, Marmara Sea, Black Sea,Sea of Azov, Catalan Sea, Ionian Sea Ligurian Sea,Tyrrhenian Sea, Gulf of Sidra, Sea of Marmara, Bay ofBiscay, Gulf of Guinea.Arctic Ocean

Hudson Bay, James Bay, Barents Sea, Kara Sea,Beaufort Sea, Amundsen Gulf, Greenland Sea, NorwegianSea, Chukchi Sea, Laptev Sea, East Siberian Sea, White Sea,Lincoln Sea, Indian Ocean, Red Sea, Gulf of Aden, PersianGulf, Gulf of Oman, Arabian Sea, Bay of Bengal,Andaman Sea, Timor Sea.Pacific Ocean

Chilean Sea, Bering Sea, Gulf of Alaska, Salish Sea,Sea of Cortez (Gulf of California), Sea of Okhotsk, Seaof Japan, Seto Inland Sea, East China Sea, South ChinaSea, Sulu Sea, Celebes Sea, Bohol Sea (Mindanao Sea)Philippine Sea, Camotes Sea, Flores Sea, Banda Sea, ArafuraSea, Timor Sea, Tasman Sea, Yellow Sea, Bohai Sea, CoralSea, Gulf of Carpentaria, Bismarck Sea, Solomon Sea,Ceram Sea, Halmahera Sea, Molucca Sea, Savu Sea, JavaSea, Gulf of Thailand.Southern Ocean

Weddell Sea, Ross Sea, Great Australian Bight, GulfSaint Vincent, Spencer Gulf, Scotia Sea, Amundsen Sea,Bellingshausen Sea, Davis Sea.Landlocked seas

Aral Sea, Caspian Sea, Dead Sea, Sea of Galilee,Salton Sea, Great Salt Lake.Ambiguous terminology

Some bodies of water that are called “seas” arenot actually seas; there are also some seas that are notcalled “seas”. The following is an incomplete list ofsuch potentially confusing names.

The Sea of Galilee is a small freshwater lake witha natural outlet, which is properly called Lake Tiberiasor Lake Kinneret on modern Israeli maps, but its archaicname remains in use.

The Sea of Cortez is more commonly known asthe Gulf of California. The Persian Gulf is a sea.

Extraterrestrial seas :Lunar maria are vast basaltic plains on the Moon

that were thought to be bodies of water by earlyastronomers, who referred to them as “seas”.

Liquid water may have existed on the surface ofMars in the distant past, and several basins on Marshave been proposed as dry sea beds. The largest isVastitas Borealis; others include Hellas Planitia andArgyre Planitia.

Liquid water is thought to be present under thesurface of several moons, most notably Europa.

Liquid hydrocarbons are thought to be present onthe surface of Titan, though it may be more accurate todescribe them as “lakes” rather than “seas”.

LakeA lake is a body of water or other liquid of

considerable size surrounded entirely by land. The vastmajority of lakes on Earth are fresh water, and most lie inthe Northern Hemisphere at higher latitudes.

In ecology the environment of a lake is referred toas lacustrine. Large lakes are occasionally referred toas “inland seas” and small seas are occasionally referredto as lakes. Many lakes are artificial and are constructedfor hydro-electric power supply, recreational purposes,industrial use, agricultural use, or domestic watersupply. Origin of natural lakes :

Geologically speaking, most lakes are young. Thenatural results of erosion will tend to wear away one ofthe basin sides containing the lake, such as the shoresof Lake Baikal in Russia which is estimated to be 25–30 million years old. There are a number of naturalprocesses that can form lakes. A recent tectonic upliftof a mountain range can create bowl-shaped depressionsthat accumulate water and form lakes. The advance andretreat of glaciers can scrape depressions in the surfacewhere lakes accumulate; such lakes are common inScandinavia, Siberia and Canada. Lakes can also formby means of landslides or by glacial blockages. Anexample of the latter occurred during the last ice age inthe state of Washington, when a huge lake formedbehind a glacial flow; when the ice retreated, the resultwas an immense flood that created the Dry Falls at SunLakes, Washington.

Salt lakes (also called saline lakes) can form wherethere is no natural outlet or where the water evaporatesrapidly, and the drainage surface of the water table hasa higher than normal salt content. Examples of salt lakesinclude Great Salt Lake, the Caspian Sea and the DeadSea.

Small, crescent-shaped lakes called oxbow lakes canform in river valleys as the result of meandering. The slow-moving river forms a sinuous shape as the outer side ofbends are eroded away more rapidly than the inner


CONCEPTS OF GEOGRAPHYside.

Lake Vostok is an subglacial lake in Antarctica,possibly the largest in the world. The pressure fromice and the internal chemical composition means thatif the lake were drilled into, it may result in a fissurewhich would spray in a similar fashion to a geyser.

Some lakes, such as Lake Baikal and LakeTanganyika lie along continental rift zones, and arecreated by the crust’s subsidence as two plates arepulled apart. These lakes are the oldest and deepest inthe world, and may be destined over millions of yearsto become oceans. The Red Sea is thought to haveoriginated as a rift valley lake.

Crater Lake in Oregon is a lake located within thecaldera of Mount Mazama. The caldera was created in amassive volcanic eruption that lead to the subsidence ofMount Mazama around 4860 BC. Since that time, alleruptions on Mazama have been confined to the caldera.

Some lakes, such as Lake Jackson come intoexistence as a result of sinkhole activity.Types of lakes

Periglacial: Part of the lake’s margin is formed byan ice sheet, ice cap or glacier, the ice having obstructedthe natural drainage of the land.

Subglacial: A lake which is permanently coveredby ice. They can occur under glaciers and ice caps orice sheets. There are many such lakes, but Lake Vostokin Antarctica is by far the largest. They are kept liquidbecause the overlying ice acts as a thermal insulatorretaining energy introduced to its underside by friction,water percolating through crevasses, by the pressurefrom the mass of the ice sheet above or by geothermalheating below.

Artificial, also called a reservoir: A lake createdby flooding land behind a dam, by human excavation,or by the flooding of an open pit mine. Some of theworld’s largest lakes are reservoirs. Husain Sagar is areservoir in India built in 1562.

Endorheic, also called terminal or closed: A lakewhich has no significant outflow, either through rivers,or underground diffusion. Any water within anendorheic basin leaves the system only throughevaporation. These lakes are most common in desertlocations, such as Lake Eyre in central Australia or theAral Sea in central Asia.Meromictic: A lake which has layers of water whichdo not intermix. The deepest layer of water in such alake does not contain any dissolved oxygen. The layersof sediment at the bottom of a meromictic lake remainrelatively undisturbed because there are no livingorganisms to stir them up.

Oxbow: A lake which is formed when a widemeander from a stream or a river is cut off to form alake. They are called oxbow lakes due to the distinctivecurved shape that results from this process.

Rift lakes: A lake which forms as a result ofsubsidence along a geological fault in the Earth’stectonic plates. Some examples are the Rift Valley lakesof eastern Africa.

Underground: A lake which is formed under thesurface of the Earth’s crust. Such a lake may be associatedwith caves and aquifers and springs. The crater lake ofVolcán Irazú, Costa Rica.

Crater: A lake which forms in volcanic calderasor craters after the volcano has been inactive for sometime. Water in these types of lakes may be fresh, orhighly acidic, and may contain various dissolvedminerals. Some also have geothermal activity, especiallyif the volcano is merely dormant rather than extinct.

Former: A lake which is no longer in existence.Such lakes include prehistoric lakes, and lakes whichhave permanently dried up through evaporation orhuman intervention. Owens Lake in California is anexample of a former lake. Former lakes are a commonfeature of the Basin and Range area of south-westernNorth America.

Shrunken: Closely related to former lakes, ashrunken lake is one which has drastically decreasedin size over geological time. Lake Agassiz is a goodexample of a shrunken lake, which covered much ofcentral North America. Some notable remnants of thislake are Lake Winnipeg, and Lake Winnipegosis.

Limnology : Limnology is the study of inlandbodies of water and related ecosystems.a

Some lakes can also disappear seasonally; they arecalled intermittent lakes and are typical of karsticterrain. A prime example of this is Lake Cerknicain Slovenia.

Extraterrestrial lakes :At present the surface of the planet Mars is too

cold and has too little atmospheric pressure to permitpooling of liquid water on the surface.However geologicevidence appears to confirm that ancient lakes onceformed on the surface. It is also possible that volcanicactivity on Mars will occasionally melt the subsurfaceice, forming large lakes. Under current conditions thiswater will quickly evaporate or freeze unless insulatedin some manner, such as by a coating of volcanic ash.

Jupiter’s small moon Io is volcanically active dueto tidal stresses, and as a result sulfur deposits haveaccumulated on the surface. Some photographs taken duringthe Galileo mission appear to show lakes of liquid sulfuron the surface.

There are dark basaltic plains on the Moon, similarto lunar maria but smaller, that are called lacus(singular lacus, Latin for “lake”). They were oncethought by early astronomers to be literal lakes.


CONCEPTS OF GEOGRAPHYNotable lakes :

The largest lake in the world by surface area isthe Caspian Sea. With a surface area of 394,299 km², ithas a surface area greater than the next six largest lakescombined.

The deepest lake is Lake Baikal in Siberia, with abottom at 1,637 m (5,371 ft.) and is the world’s largestfreshwater lake by volume.

The world’s oldest lake is Lake Baikal, followedby Lake Tanganyika (Tanzania).

The world’s highest lake is Lhagba Pool in Tibetat 6,368 m.

The world’s lowest lake is the Dead Sea, currently(2005) 418 m (1,371 ft.) below sea level. It is also one ofthe lakes with highest salt concentration.

The largest freshwater lake by surface area, andthird largest by volume, is Lake Superior with a surfacearea of 82,414 km². However, Lake Huron and LakeMichigan form a single hydrological system with surfacearea 117,350 km², sometimes designated Lake Michigan-Huron. All these are part of the Great Lakes of NorthAmerica.

The highest navigable lake is Lake Titicaca, at3,821 m above sea level. It is also the largest freshwater(and second largest overall) lake in South America.

The largest freshwater-lake island is ManitoulinIsland on Lake Huron, with a surface area of 2,766 km².Lake Manitou, located on Manitoulin Island, is thelargest lake on a freshwater-lake island.

The largest lake located on an island is NettillingLake on Baffin Island.

The largest lake in the world that drains naturallyin two directions is Wollaston Lake.

Lake Toba on the island of Sumatra is located inwhat is probably the largest resurgent caldera on Earth.

The largest lake located completely within theboundaries of a single city is Lake Wanapitei in thecity of Greater Sudbury, Ontario, Canada. Before thecurrent city boundaries came into effect in 2001, thisstatus was held by Lake Ramsey, also in Sudbury.

Lake Enriquillo is the only saltwater lake in theworld inhabited by crocodiles.Largest by continentThe largest lakes (surface area) by continent are:1. Africa - Lake Victoria, also the second largest

freshwater lake on Earth. It is one of the Great Lakesof Africa.

2. Antarctica - Lake Vostok (subglacial)3. Asia - Caspian Sea, also the largest on Earth.4. Australia - Lake Eyre5. Europe - Lake Ladoga, followed by Lake Onega,

both located in northwestern Russia.

6. North America - Lake Superior7. South America - Lake Titicaca, which is also the

highest navigable body of water on Earth at 3,821m above sea level.

Note: Lake Maracaibo can be considered as the largestlake in South America. It however lies at sea level with arelatively wide opening to sea, so it is better described as abay.Trivia :

Finland is known as The Land of the ThousandLakes (actually there are 187,888 lakes in Finland, ofwhich 60,000 are large). Minnesota is known as TheLand of Ten Thousand Lakes. The license plate of theCanadian province of Manitoba used to claim “100,000lakes” as a direct upmanship on neighboring Minnesota.

The Great Lakes of North America originated inthe ice age.

Over 60% of the world’s lakes are in Canada; thisis because of the deranged drainage system thatdominates the country.List of world’s largest lakes PositionName and location1. Caspian Sea,[1] Azerbaijan-Russia-Kazakhstan-

Turkmenistan-Iran2. Superior, U.S.-Canada3. Victoria, Kenya-Tanzania-Uganda4. Huron, U.S.-Canada5. Michigan, U.S.6. Tanganyika, Tanzania-Congo7. Baikal,[2] Russia8. Great Bear Lake, Canada9. Nyasa, Malawi-Mozambique-Tanzania10. Great Slave Lake, Canada11. Erie, U.S.-Canada12. Winnipeg, Canada13. Ontario, U.S.-Canada14. Balkhash, Kazakhstan15. Ladoga, Russia16. Aral Sea,[3] Kazakhstan-Uzbekistan17. Onega, Russia18. Titicaca, Bolivia-Peru19. Nicaragua, Nicaragua20. Athabaska, Canada21. Turkana, Kenya22. Reindeer Lake, Canada23. Eyre, South Australia24. Issyk-Kul, Kyrgyzstan25. Urmia, Iran26. Torrens, South Australia27. Vänern, Sweden28. Winnipegosis, Canada29. Albert, Uganda30. Nettilling, Baffin Island, Canada31. Nipigon, Canada32. Manitoba, Canada


CONCEPTS OF GEOGRAPHY33. Great Salt Lake, U.S.34. Kioga, Uganda

By continent

Africa - Lake VictoriaAntarctica - Lake Vostok (Subglacial lake)Asia - Caspian SeaAustralia - Lake EyreCentral America -Lake Nicaragua (second largestin Latin America, first in Central America)Europe - Lake LadogaNorth America - Lake SuperiorSouth America - Lake Maracaibo

List of world’s deepest lakes1. Baikal Siberia, Russia2. Tanganyika Africa

(Tanzania,Zaire &Zambia)3. Caspian Sea Iran and Russia4. Nyasa Africa (Mozambique,

Tanzania & Malawi)5. Issyk Kul Kyrgizstan, Central Asia6. Great Slave Northwest

Territories, Canada7. Crater Oregon, U.S.A.8. Matano Indonesia9. Hornindalsvatnet Norway10. Toba Indonesia10. Sarez Tajikistan12. Tahoe California &

Nevada, U.S.A.13. Argentino Argentina14. Chelan Washington, U.S.A.15. Kivu Congo

(Democratic Republic),Rwanda

16. Quesnel British Columbia,Canada17. Hauroko New Zealand18. Adams British Columbia,Canada19. Poso Indonesia20. Mjosa NorwayBy continent

Africa - Tanganyika, Antarctica - Vostok (Subglaciallake) , Asia - Baikal , Australia - St Clair (200 m.), CentralAmerica - Nicaragua, Europe -Hornindalsvatnet, NorthAmerica - Great Slave Lake, South America - Argentino.Island :

An island or isle is any piece of land that is completely

surrounded by water. Very small islands such asemergent land features on atolls are called islets. A keyor cay is another name for a relatively small island orislet. An island in a river or lake is called an eyot.

There are two main types of islands: continentalislands and oceanic islands. There are also artificial islands.A grouping of related islands is called an archipelago.

Also, when defining islands as pieces of land that arecompletely surrounded by water, narrow bodies of waterlike rivers and canals are generally left out ofconsideration. For instance, in France the Canal duMidi connects the Garonne river to the MediterraneanSea, thereby completing a continuous water connectionfrom the Atlantic Ocean to the Mediterranean Sea.

So technically, the land mass that includes theIberian Peninsula and the part of France that is southof the Garonne River and the Canal du Midi iscompletely surrounded by water. However, generallycases such as these are not considered islands.

Other examples of such coast-to-coastwatersystems that are not considered to cut a land massin two are the Caledonian and Forth and Clyde canalsin Scotland and the Volga-Baltic Waterway in Russia.

This also helps explain why Africa-Eurasia can beseen as one continuous landmass (and thus technicallythe biggest island): generally the Suez Canal is not seenas something that divides the land mass in two.TYPES OF ISLANDS :Continental islands

Continental islands are bodies of land that lie onthe continental shelf of a continent. Examples includeGreenland and Sable Island off North America; Barbadosand Trinidad off South America; Sicily off Europe; Sumatraand Java off Asia; and New Guinea and Tasmania offAustralia.

A special type of continental island is themicrocontinental island, which results when a continentis rifted. Examples are Madagascar off Africa; theKerguelen Islands; and some of the Seychelles.

Another subtype is an island or bar formed bydeposition of sediment where a water current losessome of its carrying capacity. An example is barrierislands, which are accumulations of sand deposited bysea currents on the continental shelf. Another exampleis islands in river deltas or in large rivers. While someare transitory and may disappear if the volume or speedof the current changes, others are stable and long-lived.Oceanic islands

Oceanic islands are ones that do not sit oncontinental shelves. They are volcanic in origin. Onetype of oceanic island is found in a volcanic island arc.These islands arise from volcanoes where the subductionof one plate under another is occurring. Examplesinclude the Mariana Islands, the Aleutian Islands,Republic of Mauritius and most of Tonga in the Pacific


CONCEPTS OF GEOGRAPHYOcean. Some of the Lesser Antilles and the SouthSandwich Islands are the only Atlantic Ocean examples.

Another type of oceanic island occurs where anoceanic rift reaches the surface. There are two examples:Iceland, which is the world’s largest volcanic island, andJan Mayen — both are in the Atlantic.

Wake Island is a volcanic island that has becomean atoll.A third type of oceanic island is formed overvolcanic hotspots.An example is the Hawaiian Islands,from Hawaii to Kure, which then extends beneath thesea surface in a more northerly direction as theEmperor Seamounts. Another chain with similarorientation is the Tuamotu Archipelago; its older,northerly trend is the Line Islands. The southernmostchain is the Austral Islands, with its northerly trendingpart the atolls in the nation of Tuvalu. Tristan da Cunhais an example of a hotspot volcano in the AtlanticOcean. Another hot spot in the Atlantic is the island ofSurtsey, which was formed in 1963.

An atoll is an island formed from a coral reef thathas grown on an eroded and submerged volcanic island.The reef rises to the surface of the water and forms anew island. Atolls are typically ring-shaped with a centrallagoon. Examples include the Maldives in the Indian Oceanand Line Islands in the Pacific.List of Islands by Area

This is a list of islands in the world ordered by area.It includes all islands with an area greater than 2,500 km²(970 square miles). For comparison, continental landmassesare also shown.Continental land massesThese figures are rough approximations only.Rank Continent Area(km²) Area(sq mi)1 Africa-Eurasia 84,000,000 32,000,0002 The Americas 41,000,000 16,000,0003 Antarctica 13,000,000 5,000,0004 Australia 7,600,000 2,900,000Note: Australia, at 7,600,000 km², is considered to be acontinental landmass, rather than an island. Australia ismuch larger than Greenland, the largest island.Islands over 2,500 km²Rank Island’s Name Area Country/

(km²) Countries1 Greenland 2,130,800 Greenland, a self-

governed territory ofDenmark

2 New Guinea 785,753 Indonesia and PapuaNew Guinea

3 Borneo 748,168 Brunei, Indonesiaand Malaysia

4 Madagascar 587,713 Madagascar5 Baffin Island 507,451 Canada6 Sumatra 443,066 Indonesia

7 Honshû 225,800 Japan8 Great Britain 218,595 United Kingdom9 Victoria Island 217,291 Canada10 Ellesmere Island Canada11 Sulawesi 180,681 Indonesia12 South Island

of New Zealand145,836 New Zealand13 Java 138,794 Indonesia14 North Island of

New Zealand 111,583 New Zealand15 Luzon 109,965 Philippines16 Newfoundland 108,860 Canada17 Cuba main island 105,806 Cuba18 Iceland main island 101,826 Iceland19 Mindanao 97,530 Philippines20 Ireland 81,638 Republic of Ireland

and UnitedKingdom


CONCEPTS OF GEOGRAPHYEARTH REVOLUTION AND ROTATION

Earth, the third planet of our solar system revolvesaround the Sun once every 365 1/4 days. The orbit ofthe Earth around the sun is called Earth revolution. Thiscelestial motion takes 365 1/4 days to complete one cycle.Further, the Earth’s orbit around the sun is not circular,but elliptical .An elliptical orbit causes the Earth’s distancefrom the sun to vary annually. However, this phenomenon

does not cause the seasons! This annual variation in thedistance from the sun does influence the amount of solarradiation intercepted by the Earth by approximately 6%.The elliptical orbit of the earth varies from 91.5 millionmiles on January 3 called “perihelion”, to 94.5 millionmiles on July 4 called “aphelion” for an average earth-sun distance of 93 million miles. The elliptical path causesonly small variations in the amount of solar radiationreaching the earth.Figure: Earth’s elliptical orbit

The Earth rotates at a uniform rate on its axis onceevery 24 hours. The term Earth rotation refers to thespinning of the Earth on its axis. One rotation takes exactlytwenty-four hours and is called a mean solar day. Turningin an eastward direction the Sun “rises” in the east andseemingly “travels” toward the west during the day. TheSun isn’t actually moving, it’s the eastward rotation towardsthe morning Sun that makes it appear that way. The Earththen rotates in the opposite direction to the apparent pathof the Sun. Looking down from the North Pole yields acounterclockwise direction. From over the South Pole aclockwise direction of rotation occurs.

Axial Tilt: The Earth’s axis is not perpendicular tothe plane of the ecliptic, but inclined at a fixed angle of

23.5°. Moreover, the northern end ofthe Earth’s axis always points to thesame place in space (North Star/polar star). The axis is tilted in thesame direction throughout a year;however, as the Earth orbits the Sun,the hemisphere (half part of earth)

tilted away from the Sun will gradually come to be tiltedtowards the Sun, and vice versa. This effect is the maincause of the seasons. Whichever hemisphere is currentlytilted toward the Sun experiences more hours of sunlighteach day, and the sunlight at midday also strikes the groundat an angle nearer the vertical and thus delivers more heat

are some of the factors influencing the seasonalpheniomena.PARALLELISM:

As a result of Earth’s axis tilt of 23 1/2 degreesfrom being perpendicular to theplane of the ecliptic, the axis ofrotation remains pointing in thesame direction as it revolvesaround the Sun, pointing towardthe star Polaris. As a result, theEarth’s axis of rotation remainsparallel to its previous position asit orbits the sun, a property called“parallelism”. Axis Tilt and Solar Altitude

The constant tilt and parallelism causes changes in theangle that a beam of light makes with respect to a pointon Earth during the year, called the “sun angle”. The mostintense incoming solar radiation occurs where the sun’s raysstrike the Earth at the highest angle. As the sun angledecreases, the beam of light is spread over a larger areaand decreases in intensity. During the summer months theEarth is inclined toward the Sun yielding high sun angles.During the winter, the Earth is oriented away from theSun creating low sun angles. The tilt of the Earth and itsimpact on sun angle is the reason the Northern and

Southern Hemisphere have oppositeseasons. Summer occurs when ahemisphere is tipped toward the Sunand winter when it is tipped awayfrom the Sun.

Path length and Insolation :The distance that a beam of light travels greatly

affects the amount of solar energy that ultimatelyreaches the Earth. The Earth-Sun distance only variesby about 3 million miles compared to an averagedistance of about 93 million miles over the year. A moresignificant impact on insolation is the thickness of theatmosphere on depletion of a beam of light. As theamount of atmosphere through which the beam passesincreases, the greater the chance for reflection andscattering of light, thus reducing insolation at the surface.Due to the curvature of the Earth, a beam of lightstriking the Equator passes through less atmosphere than


CONCEPTS OF GEOGRAPHYone at a higher latitude.

The Earth’s axis always remains pointing in thesame direction as it revolves around the sun. As a result,the solar angle varies at a given place throughout theyear. The variation in sun angle is the prime cause ofour seasons. The orientation of the Earth with respectto the Sun also determines the length of day. Together,the sun angle and day length determine the total amountof solar radiation incident at the Earth.. The annualchange in the relative position of the Earth’s axis inrelationship to the sun causes the height of the sun (solaraltitude) to vary in our skies. The total variation inmaximum solar altitude for any location on the Earthover a one year period is 47° (2 x 23.5 = 47). Forexample, at 50° North maximum solar altitude variesfrom 63.5° on the summer solstice to 16.5° on the wintersolstice . Maximum solar height at the equator goesfrom 66.5° above the northern end of the horizon duringthe summer solstice, to directly overhead on the fallequinox, and then down to 66.5° above the southernend of the horizon during the summer solstice

On about June 21st or June 22nd the Northernhemisphere is tipped toward the sun. At noon, the subsolarpoint, or place where the sun lies directly overhead at noon,is located at 23 1/2o north latitude. This date is known asthe summer solstice, the longest day of the year for placeslocated north of Tropic of Cancer. The 23 1/2o parallelwas so named because it is during the astrological signCancer when the Sun’s rays strike at their highest angle ofthe year north of this line. The North pole tips into theSun and tangent rays strike at the Arctic and AntarcticCircles. (A tangent ray is one that meets a curve or surfacein a single point). This creates a 24 hour period of daylight(“polar day”) for places located poleward of 66 1/2o north.We find the South Pole tipped away from the Sun, sendingplaces poleward of 66 1/2o south into 24 hours of darkness(“polar night”).

On Sept 22nd or 23rd, the Earth has moved aroundthe Sun such that the poles are neither pointing toward oraway from the sun. On this day, the Sun is directly overhead0 degrees, the equator, at noon. Tangent rays strike at thepoles. It is the autumnal equinox and all places experience12 hours of day light and 12 hours of darkness.

The winter solstice occurs on December 21st or22nd when the Earth has oriented itself so the NorthPole is facing away from, and theSouth Pole into the Sun. Again,tangent rays strike at the Arcticand Antarctic circles. Placespoleward of 66 1/2o north are inthe grips of the cold, polar night.Places poleward of 66 1/2o southexperience the 24 hour polar day.The Sun lies directly over 23 1/2o

south. Occurring during theastrological sign of Capricorn, 231/2o south latitude is called the

Tropic of Capricorn.Continuing to March 20th or 21st (i.e. Spring

Equinox) the Earth has positioned itself similar to thatwhich occurs in September, only on the other side ofthe Sun. Once again tangent rays strike at the Northand South poles, and the perpendicular rays of the Sunstrike the Equator at noon . All places have equal daylength (12 hours day;12 hours of night) as the circle ofillumination cuts all latitudes in half.

So over the course of a year, the Sun’s rays areonly perpendicular to the surface (directly over head)at places between 23 1/2o north and south. Placesbetween the Tropic of Cancer and Capricorn experiencetwo times when the Sun is directly over head over thecourse of a year. The sun angle does not vary much forplaces between 23 1/2o north and south, a larger rangein sun angle occurs poleward of these latitudes. Thegreater the variation in sun angle, the greater thevariation in surface heating.

Day length and seasonsDay length is determined by the length of time the

Sun is above the horizon. Day length changes throughthe year as the orientation of the Earth to the Sunchanges. The circle of illumination is the imaginarycircle that separate day from night.

Figure shows two extreme cases, the December andJune solstices. Note during December that more of agiven latitude in the Southern hemisphere is exposed tothe Sun. This is the longest day of the year for thoseliving poleward of the Equator. In June the oppositeoccurs with longer day length in the Northern

March EQUINOX

DECEMBER SOLSTICE

SEPTEMBER EQUINOX JUNE SOLSTICE

Date March 21 December 22 Sept. 23 June 21 Subsolar

Point 0o 23 1/2o S 0o 23 1/2o N

Tangent Rays

North and South Poles

Arctic and Antarctic Circles

North and South Poles

Arctic and Antarctic Circles

Day length 12 hour day length everywhere

24 hours of darkness at North Pole; 24 hours day light at

South Pole; 12 hours day light at Equator

12 hour day length everywhere

24 hours of darkness at South Pole; 24 hours day light at

North Pole; 12 hours day light at Equator


CONCEPTS OF GEOGRAPHYLATITUDE

Latitude, usually denoted symbolically by theGreek letter phi, , gives the location of a place onEarth north or south of the Equator.

Latitude is an angular measurement in degrees(marked with °) ranging from 0° at the Equator to 90°at the poles (90° N for the North Pole or 90° S for theSouth Pole). The distance between the successiveLatitudes, always corresponds to exactly sixty nauticalmiles or about 111 km (69 statute miles, each of 5280feet).Circles of latitude

All locations of a given latitude are collectivelyreferred to as a circle of latitude or line of latitude or parallel,because they are coplanar, and all such planes areparallel to the Equator.

Lines of latitude other than the Equator areapproximately small circles on the surface of the Earth;they are not geodesics since the shortest route betweentwo points at the same latitude involves moving fartheraway from, then towards, the equator ( great circle).

A specific latitude may then be combined with aspecific longitude to give a precise position on theEarth’s surface .Circle of latitude

On the Earth, a circle of latitude or parallel is animaginary east-west circle that connects all locations witha given latitude.

The position on the circle of latitude is given by thelongitude. Each is perpendicular to all meridians at theintersection points.

Those parallels closer to the poles are smaller thanthose at or near the Equator.

For a low latitude a circle of latitude can be said tobe a line around the Earth, while at a high latitude it is acircle around a pole.MAJOR LATITUDESEquator

The equator is the circle that is equidistant from boththe North Pole and South Pole. It splits the Earth into theNorthern Hemisphere and the Southern Hemisphere.Arctic and Antarctic Circles

The Arctic Circle represents the southernmost locationin the Northern Hemisphere where it is possible to have aday without a sunrise (see midnight sun).

Respectively, the Antarctic Circle represents thenorthernmost location in the Southern Hemisphere whereit is possible to have a day without a sunrise.

The latitude plus the axial tilt is equal to 90°.Tropic of Cancer and Capricorn

The Tropic of Cancer and Tropic of Capricornrepresent the northernmost and southernmost locations

where the sun may be seen directly overhead(midsummer and midwinter respectively). Note that thelatitude of is equal to the axial tilt.NOTABLE PARALLELSParallel Description49th parallel north Part of the border between the

United States and Canada, fromWashington to western Minnesota.

45th parallel north The border between Vermont andQuebec.

42nd parallel north The border between California andOregon.

41st parallel north Parts of the borders of Colorado,Utah, Wyoming, and Nebraska.

40th parallel north The line originally chosen for theMason-Dixon Line, but the line wasmoved several miles south to avoidbisecting the city of Philadelphia.

39° 432 19.922163N Mason-Dixon line38th parallel north Boundary between the Soviet and

American occupation zones in Koreain 1945.

37th parallel north North-south border between Utah &Arizona, and Colorado & NewMexico respectively.

33rd parallel north The border between Louisiana andArkansas

30th parallel north ?28th parallel north Boundary between Baja California

and Baja California Sur in Mexico.22° 19' 35.6736" N Boundary Street - Boundary between

Kowloon and New Kowloon ofNew Territories

17th parallel north Division between Republic ofVietnam (South Vietnam) andDemocratic Republic of Vietnam(North Vietnam) during the Vietnamwar.

45th parallel south ?60th parallel south Area south of which is considered

Antarctica for the purposes of theAntarctic Treaty System (see map)

Important named circles of latitudeFour lines of latitude are named because of the role

they play in the geometrical relationship with the Earthand the Sun:

• Arctic Circle — 66° 332 393 N• Tropic of Cancer — 23° 262 223 N• Tropic of Capricorn — 23° 262 223 S• Antarctic Circle — 66° 332 393 SOnly at latitudes between the Tropics is it possible

for the sun to be at the zenith. Only north of the ArcticCircle or south of the Antarctic Circle is the midnight sunpossible.

The reason that these lines have the values that they


CONCEPTS OF GEOGRAPHYdo lies in the axial tilt of the Earth with respect to thesun, which is 23° 262 223 .

The Arctic Circle & Tropic of Cancer and theAntarctic Circle and Tropic of Capricorn are colatitudessince the sum of their angles is 90°.

LongitudeLongitude, sometimes denoted by the Greek letter

ë (lambda), describes the location of a place onEarth east or west of a north-south line called the PrimeMeridian.

Longitude is given as an angular measurementranging from 0° at the Prime Meridian to +180°eastward and “180° westward.

In 1884, the International Meridian Conferenceadopted the Greenwich meridian as the universal primemeridian or zero point of longitude.

Each degree of longitude is further sub-divided into60 minutes, each of which divided into 60 seconds. Alongitude is thus specified as 23° 272 30" E. For highaccuracy, the seconds are specified with a decimal fraction.

An alternative representation uses degrees and minutes,where parts of a minute are expressed as a decimal fraction,thus: 23° 27.5002 E. Degrees may also be expressed as adecimal number: 23.45833° E. Sometimes, the West/Eastsuffix is replaced by a negative sign for West.

A specific longitude may then be combined witha specific latitude to give a precise position on theEarth’s surface.

As opposed to a degree of latitude, which alwayscorresponds to exactly sixty nautical miles or about 111km (69 statute miles, each of 5280 feet), a degree oflongitude corresponds to a distance that varies from 0to 111 km.

It is 111 km times the cosine of the latitude, whenthe distance is laid out on a circle of constant latitude.

Longitude at a point may be determined by calculatingthe time difference between that at its location andCoordinated Universal Time (UTC). Since there are 24hours in a day and 360 degrees in a circle, the sun movesacross the sky at a rate of 15 degrees per hour (360°/24hours = 15° per hour).

So if the time zone a person is in is three hours aheadof UTC then that person is near 45° longitude (3 hours ×15° per hour = 45°).

A line of constant longitude is a meridian, and halfof a great circleTime zones

A time zone is a region of the Earth that has adoptedthe same standard time, usually referred to as the localtime. Most adjacent time zones are exactly one hour apart,and by convention compute their local time as an offsetfrom Greenwich Mean Time.(where 00 prime meridian starts)

Standard time zones can be defined by geometrically

subdividing the Earth’s spheroid into 24 lunes (wedge-shaped sections), bordered by meridians each 15° oflongitude apart. The local time in neighbouring zones isthen exactly one hour different.

However, political and geographical practicalitiescan result in irregularly-shaped zones that followpolitical boundaries or that change their time seasonally(as with daylight saving time), as well as being subjectto occasional redefinition as political conditions change.Standard time zones

Originally, time zones based their time onGreenwich Mean Time (GMT, also called UT1), themean solar time at longitude 0° (the Prime Meridian).But as a mean solar time, GMT is defined by therotation of the Earth, which is not constant in rate. So,the rate of atomic clocks was annually changed orsteered to closely match GMT.SNIPPETS• In terms of the largest number of time zones, Russia

is first, with eleven time zones, including Kaliningradon the Baltic Sea. The United States is tied withCanada for second with six time zones. If thepossessions of the United Kingdom, the United Statesand France are included it increases the number oftime zones in each. Taking into account overseasterritories and possessions, France is the largest, withover twelve time zones, the United States has ninetime zones, and the United Kingdom has over eighttime zones.

• In terms of area, China is the largest country withonly one time zone (UTC+8), although before theChinese Civil War in 1949 China was separated intofive time zones. China also has the widest spanningtime zone.

• Stations in Antarctica generally keep the time of theirsupply bases, thus both the Amundsen-Scott SouthPole Station (U.S.) and McMurdo Station (U.S.) useNew Zealand time (UTC+12 southern winter,UTC+13 southern summer).

• The 27° latitude passes back and forth across timezones in South Asia. Pakistan: +5, India +5:30, Nepal+5:45, India (Sikkim) +5:30, China +8:00, Bhutan+6:00, India (Arunachal Pradesh) +5:30, Myanmar+6:30. This switching was more odd in 2002, whenPakistan enabled Daylight Saving Time. Thus fromwest to east, time zones were: +6:00, +5:30, +5:45,+5:30, +8:00, +6:00, +5:30 and +6:30.

• Because the earliest and latest time zones are 26 hoursapart, any given calendar date exists at some point onthe globe for 50 hours. For example, April 11 beginsin time zone UTC+14 at 10:00 UTC April 10, andends in time zone UTC-12 at 12:00 UTC April 12.

• There are numerous places where several time zonesmeet, for instance at the tri-country border of Finland,Norway and Russia.


CONCEPTS OF GEOGRAPHY• There are about 39 time zones instead of 24 (as

popularly believed). This is due to fractional houroffsets and zones with offsets larger than 12 hoursnear the International Date Line. Some micronationsmay use offsets that are not recognized by allauthorities.

• The largest time gap along a political border is the3.5 hour gap along the border of China (UTC +8)and Afghanistan (UTC+4:30).

• One of the most unusual time zones is the AustralianCentral Western Time zone (CWST), which is in effectin a small strip of Western Australia from the borderof South Australia west to just before Caiguna. It is8¾ hours ahead of UTC (UTC+8:45) and covers anarea of about 35,000 km², larger than Belgium, buthas a population of about 200. Although unofficial,it is universally respected in the area. See Time inAustralia.

Prime MeridianThe Prime Meridian , also known as the

International Meridian or Greenwich Meridian, is themeridian (line of longitude) passing through the RoyalGreenwich Observatory, Greenwich, England — it is themeridian at which longitude is defined to be 0 degrees.The prime meridian, and the opposite 180th meridian (at180° longitude), which the International Date Line generallyfollows, separate the Eastern and Western Hemispheres.

Heading south from the North Pole, the PrimeMeridian passes through the following countries:• United Kingdom (The most northernly land on the

meridian is the shore (53°45’34"N) southeast of theSand-le-Mere caravan park east of Kingston uponHull, England.) ,France ,Spain ,Algeria ,Mali ,BurkinaFaso, Togo Ghana ,Antarctica to the South PoleThe zero meridian used by satellite navigation systems

(on the WGS84 datum) is 102.5 metres (336.3 feet) to theeast of the line marked at Greenwich.International Date Line

The International Date Line (IDL), also known asjust the Date Line, is an imaginary line on the surface ofthe Earth opposite the Prime Meridian which offsets thedate as one travels east or west across it.

Roughly along 180° longitude, with diversions to passaround some territories and island groups, it correspondsto the time zone boundary separating +12 and -12 hoursGMT (UT1).

For the most part, the International Date Line followsthe meridian of 180° longitude, roughly down the middleof the Pacific Ocean. However, because the date to theeast of the line is one day earlier than that to the west ofthe line, the line deviates to pass around the far east ofRussia and various island groups in the Pacific, no countrywanting to have, at least during ordinary daytime hours, itscitizens functioning on two different dates. Thus, the twolargest deviations from this meridian both occur to keep

the date line from crossing nations internally.In the north, the date line swings to the east through

Bering Strait and then west past the Aleutian Islands inorder to keep Alaska (part of the United States) and Russiaon opposite sides of the line and their territories duenorth and south of each other in concert with the dateof the rest of each respective country.

In the central Pacific, the date line was moved in1995 to extend around, rather than through, the islandsof the Republic of Kiribati. As a British colony, Kiribatiwas centered in the Gilbert Islands, just west of theInternational Dateline. Upon independence in 1979, the newrepublic acquired the Phoenix and Line Islands from theUnited States and the country found itself straddling thedate line. Government offices on opposite sides of the linecould only communicate on the four days of the week whenboth sides experienced weekdays simultaneously. Aconsequence of this time zone revision was that Kiribati,by virtue of its easternmost possession, uninhabitedCaroline Atoll at 150°25’W, started on its territory the year2000 before any other country on earth, a feature whichthe Kiribati government capitalized upon as a potentialtourist draw. However, even into the 21st century, manymapmakers are not aware of this Kiribati dateline shiftand continue to represent the International Date as astraight line in the Kiribati area.

In the South Pacific, the dateline swings east such thatvarious islands administered by New Zealand (which lieswest of 180°) are on the same date with New Zealand.

The International Date Line can cause confusionamong airline travelers. The most troublesome situationusually occurs with short journeys from west to east. Forexample, to travel from Tonga to Samoa by air takesapproximately two hours, but involves crossing theinternational date line, causing the passenger to arrive theday before they left. This often causes confusion in travelschedules.

If someone circumnavigates the globe in an airplanefrom east to west (the same direction as Magellan), heshould subtract one hour for every 15° of longitudecrossed, losing 24 hours for one circuit of the globe. But24 hours are added when crossing the International DateLine (from east to west). The International Date Line musttherefore be observed in conjunction with earth’s timezones: the net adjustment to one’s watch is zero. If onecrosses the date line at precisely midnight, going westward,one skips an entire day; while going eastward, one repeatsthe entire day.


CONCEPTS OF GEOGRAPHYThe motion of the air is not directly north and

south but is affected by the momentum the air has as itmoves away from the equator. The reason has to dowith momentum and how fast a location on or abovethe Earth moves relative to the Earth’s axis.

Your speed relative to the Earth’s axis depends onyour location. Someone standing on the equator ismoving much faster than someone standing on a 45°

latitude line. In the graphic (left) the person at theposition on the equator arrives at the yellow line soonerthan the other two. Someone standing on a pole is notmoving at all (except that he or she would be slowlyspinning). The speed of the rotation is great enough tocause you to weigh one pound less at the equator thanyou would at the north or south pole.

The momentum the air has as it travels around theearth is conserved, which means as the air that’s overthe equator starts moving toward one of the poles, itkeeps its eastward motion constant. The Earth belowthe air, however, moves slower as that air travels towardthe poles. The result is that the air moves faster andfaster in an easterly direction (relative to the Earth’ssurface below) the farther it moves from the equator.

In addition, with the three-cell circulationsmentioned previously, the regions around 30° N/S and50°-60° N/S are areas where temperature changes arethe greatest. As the difference in temperature betweenthe two locations increase, the strength of the windincreases. Therefore, the regions around 30° N/S and50°-60° N/S are also regions where the wind, in theupper atmosphere, is the strongest.

The 50°-60° N/S region is where the polar jetlocated with the subtropical jet located around 30°N.Jet streams vary in height of four to eight miles andcan reach speeds of more than 275 mph. The actualappearance of jet streams result from the complexinteraction between many variables - such as the locationof high and low pressure systems, warm and cold air,and seasonal changes. They meander around the globe,dipping and rising in altitude/latitude, splitting at timesand forming eddies, and even disappearing altogetherto appear somewhere else.

Jet streams also “follow the sun” in that as thesun’s elevation increases each day in the spring, the jetstreams shifts north moving into Canada by Summer.As Autumn approaches and the sun’s elevationdecreases, the jet stream moves south into the UnitedStates helping to bring cooler air to the country.


CONCEPTS OF GEOGRAPHYEARTH’S ATMOSPHERE

Earth’s atmosphere is a layer of gases surroundingthe planet Earth and retained by the Earth’s gravity.

It contains roughly 78% nitrogen and 21% oxygen0.97% argon and carbon dioxide 0.04% trace amounts ofother gases, and water vapor.

This mixture of gases is commonly known as air.The atmosphere protects life on Earth by absorbing

ultraviolet solar radiation and reducing temperature extremesbetween day and night.

Three-quarters of the atmosphere’s mass is within11 km of the planetary surface.

In the United States, persons who travel above analtitude of 50.0 miles (80.5 km) are designated asastronauts.

An altitude of 120 km (75 mi or 400,000 ft) marksthe boundary where atmospheric effects become noticeableduring re-entry.

The Karman line, at 100 km (62 mi), is alsofrequently used as the boundary between atmosphereand space.

The average temperature of the atmosphere at thesurface of earth is 14 °C.

PressureAtmospheric pressure is a direct result of the

weight of the air. This means that air pressure varieswith location and time, because the amount (and weight)of air above the earth varies with location and time.Atmospheric pressure drops by 50% at an altitude ofabout 5 km (equivalently, about 50% of the totalatmospheric mass is within the lowest 5 km). Theaverage atmospheric pressure, at sea level, is about 101.3kilopascals (about 14.7 pounds per square inch).Thickness of the atmosphere

Even at heights of 1000 km and above, theatmosphere is still present (as can be seen for example bythe effects of atmospheric drag on satellites).

However:57.8% of the atmosphere by mass is belowthe summit of Mount Everest.

72% of the atmosphere by mass is below the commoncruising altitude of commercial airliners (about 10000 mor 33000 ft).

99.99999% of the atmosphere by mass is below thehighest X-15 plane flight on August 22, 1963, whichreached an altitude of 354,300 ft or 108 km.

Therefore, most of the atmosphere (99.9999%) bymass is below 100 km, although in the rarefied region abovethis there are auroras and other atmospheric effects.

CompositionHeterosphere

Below the turbopause at an altitude of about 100

km, the Earth’s atmosphere has a more-or-less uniformcomposition (apart from water vapor) as described above;this constitutes the homosphere.However, above about 100km, the Earth’s atmosphere begins to have a compositionwhich varies with altitude. This is essentially because, inthe absence of mixing, the density of a gas falls offexponentially with increasing altitude, but at a rate whichdepends on the molar mass. Thus higher mass constituents,such as oxygen and nitrogen, fall off more quickly thanlighter constituents such as helium, molecular hydrogen, andatomic hydrogen. Thus there is a layer, called theheterosphere, in which the earth’s atmosphere has varyingcomposition. As the altitude increases, the atmosphere isdominated successively by helium, molecular hydrogen, andatomic hydrogen. The precise altitude of the heterosphereand the layers it contains varies significantly withtemperature.

* The mean molar mass of air is 28.97 g/mol

Density and massThe density of air at sea level is about 1.2 kg/m3. The atmospheric density decreases as the altitude

increases.This variation can be approximately modeled using the

barometric formula. More sophisticated models are usedby meteorologists and space agencies to predict weatherand orbital decay of satellites.

The average mass of the atmosphere is about 5,000trillion metric tons.

According to the National Center for AtmosphericResearch, The mean mass of water vapor is estimated as1.27×1016 kg and the dry air mass as 5.1352 ±0.0003×1018

kg.By mass, the composition of the atmosphere is

75.523% nitrogen, 23.133% oxygen, 1.288% argon, 0.053%carbon dioxide, 0.001267% neon, 0.00029% methane,0.00033% krypton, 0.000724% helium, and 0.0000038 %hydrogen.

Temperature and the atmospheric layersThe temperature of the Earth’s atmosphere varies

with altitude; the mathematical relationship betweentemperature and altitude varies between the differentatmospheric layers OF THE ATMOSPHERE.

Troposphere: From the Greek word “tropos”meaning to turn or mix.

The troposphere has a great deal of vertical mixingdue to solar heating at the surface. This heating warms airmasses, which then rise to release latent heat as sensibleheat that further uplifts the air mass. This processcontinues until all water vapor is removed. In thetroposphere, on average, temperature decreases withheight due to expansive cooling.

stratosphere: from Earth’s surface to the top of thestratosphere (50km) is just under 1% of Earth’s radius


CONCEPTS OF GEOGRAPHYThe Troposphere

is the lowermostportion of Earth’satmosphere. It is thedensest layer of theatmosphere andcontains approximately75% of the mass of theatmosphere and almostall the water vapor andaerosol.

The troposphereextends from the Earth’ssurface up to thetropopause where thestratosphere begins.

The depth of thetroposphere is greatest inthe tropics (about 16km)and smallest at the poles(about 8km).

The lower part,where friction on theEarth’s surface influenceswith air flow, is theplanetary boundary layeror peploshere which is 2km deep on average,dependent on thelandform, and which isseparated from the restof the tropospere by thecapping inversion layer.

The troposphere isthe most turbulent partof the atmosphere and isthe part of theatmosphere in whichmost weatherphenomena are seen.Generally, jet aircraft flyjust above thetroposphere to avoidturbulence.

In the tropospherethe temperaturedecreases with height atan average rate of 6.4°C for every 1 kmincrease in height. Thisdecrease in temperatureis caused by adiabaticcooling –( as air rises, theatmospheric pressure falls andso the air expands). This iscalled normal lapse rate

of atmospheric temparatureTemperatures decrease at middle latitudes from

approx. +17°C at sea level to approx. -52°C at thebeginning of the tropopause.

At the poles, the troposphere is thinner and thetemperature only decreases to -45 °C, while at the equatorthe temperature at the top of the troposphere can reach -75 °C.The tropopause:

The tropopause is the boundary region between thetroposphere and the stratosphere.

Measuring the temperature change with heightthrough the troposphere and the stratosphere identifiesthe location of the tropopause.

In the troposphere, temperature decreases withaltitude. In the stratosphere, however, the temperature

increases with altitude.The region of the atmosphere where the lapse rate

changes from positive (in the troposphere) to negative (inthe stratosphere), is defined as the tropopause.

stratosphere: The stratosphere is a layer of Earth’satmosphere that is stratified in temperature, with warmer layershigher up and cooler layers farther down.

This is in contrast to the troposphere near the Earth’ssurface, which is cooler higher up and warmer farther down. Thestratosphere is situated between about 10 km and 50 kmaltitude above the surface at moderate latitudes, while at the polesit starts at about 8 km altitude.

The stratosphere is layered in temperature because itis heated from above by absorption of ultraviolet radiationfrom the Sun.

Within this layer, temperature increases as altitude increases;the top of the stratosphere has a temperature of about270 K, about the same as the ground level temperature.This top is called the stratopause, above which temperatureagain decreases with height.

The vertical stratification, with warmer layers aboveand cooler layers below, makes the stratospheredynamically stable: there is no regular convection andassociated turbulence in this part of the atmosphere.

The heating is caused by an ozone layer that


CONCEPTS OF GEOGRAPHYabsorbs solar ultraviolet radiation, heating the upperlayers of the stratosphere.

Commercial airliners typically cruise at an altitudenear 10 km in temperate latitudes, in the lower reachesof the stratosphere. This is to avoid atmosphericturbulence from the convection in the troposphere.

Turbulence experienced in the cruise phase offlight is often caused by convective overshoot from thetroposphere below. Similarly, most gliders soar on thermalplumes that rise through the troposphere above warmpatches of ground; these plumes end at the base of thestratosphere, setting a limit to how high gliders can fly inmost partsof the world. (Some gliders do fly higher, usingwave lift from mountain ranges to lift them into thestratosphere.)

The stratosphere is a region of intense interactionsamong radiative, dynamical, and chemical processes, inwhich horizontal mixing of gaseous components proceedsmuch more rapidly than vertical mixing.

An interesting feature of stratospheric circulation isthe quasi-Biennial Oscillation (QBO) in the tropicallatitudes, which is driven by gravity waves that areconvectively generated in the troposphere

The QBO induces a secondary circulation that isimportant for the global stratospheric transport of tracerssuch as ozone or water vapor.In northern hemispheric winter,sudden stratospheric warmings can often be observed whichare caused by the absorption of Rossby waves in thestratosphere.

The stratopause is the level of the atmospherewhich is the boundary between two layers, stratosphereand the mesosphere. In the stratosphere the temperatureincreases with altitude, and the stratopause is the sectionwhere a maximum in the temperature occurs.Thisoccurs not only on Earth, but on other planets with anatmosphere as well.

On Earth, the stratopause is 50 to 55 km high abovethe earths surface. The atmospheric pressure is around 1/1000th of the pressure at sea level.Mesosphere

The mesosphere (from the Greek words mesos = middleand sphaira = ball) is the layer of the Earth’s atmospherethat is directly above the stratosphere and directly belowthe thermosphere.

The mesosphere is located about 50-80/85km aboveEarth’s surface. Within this layer, temperature decreases withincreasing altitude.

The main dynamical features in this region are theatmospheric tides which are driven by momentumpropagating upwards from the lower atmosphere andextending into the lower thermosphere.

Because it lies between the maximum altitude for mostaircraft and the minimum altitude for most spacecraft, this regionof the atmosphere has only been accessed through the use ofsounding rockets. As a result the region is one of the most

poorly understood in the atmosphere. This has led themesosphere and the lower thermosphere to be jokinglyreferred to by scientists as the ignorosphere.

Temperatures in the upper mesosphere fall as lowas -100°C (-146°F or 173 K) varying according to latitudeand season.

Millions of meteors burn up daily in the mesosphereas a result of collisions with the gas particles containedthere, leading to a high concentration of iron and othermetal atoms. The collisions almost always create enoughheat to burn the falling objects long before they reachthe ground.The stratosphere and mesosphere arereferred to as the middle atmosphere.

This is also around the same altitude as theturbopause, below which different chemical species are wellmixed due to turbulent eddies. Above this level the scaleheights of different chemical species will differ.

Noctilucent clouds of thin layers are located inthe mesosphere.Their presence can be attributed to themeteoric dust which act as a nucleus for ice crystalswhen some amount of traces of water vapour are carriedup by convection currents and making up some clouds.

MESOPAUSE: The mesopause, at an altitude ofabout 80-85 km, separates the mesosphere from thethermosphere—the second-outermost layer of the Earth’satmosphere. Noctilucent clouds with the increasing altitude.

This is also around the same altitude as theturbopause*, below which different chemical species are wellmixed due to turbulent eddies. Above this level the scaleheights of different chemical species will differ.

*Turbopause:The turbopause marks the altitude inthe Earth’s atmosphere below which turbulent mixingdominates. The region below the turbopause is known asthe homosphere, where the chemical constituents are wellmixed and display identical height distributions; in otherwords, the chemical composition of the atmosphere remainsconstant in this region.

The region above the turbopause is the heterosphere,where molecular diffusion dominates and the chemicalcomposition of the atmosphere varies according tochemical species.The turbopause lies near themesopause, at the intersection of the mesosphere andthe thermosphere, at an altitude of roughly 100 km.

Thermosphere:The thermosphere is the layer of the earth’s

atmosphere directly above the mesosphere and directlybelow the exosphere. Within this layer, ultravioletradiation causes ionization. It is the fourth atmosphericlayer from earth.

The thermosphere, named from the Greek (thermos)for heat, begins about 85 km above the earth. At thesehigh altitudes, the residual atmospheric gases sort intostrata according to molecular mass .

Thermospheric temperatures increase with altitudedue to absorption of highly energetic solar radiation by


CONCEPTS OF GEOGRAPHYthe small amount of residual oxygen still present.

Temperatures are highly dependent on solaractivity, and can rise to 2,000°C. Radiation causes theair particles in this layer to become electrically charged ,enabling radio waves to bounce off and be receivedbeyond the horizon.

Even though the temperature is so high, one willnot feel warm in the thermosphere due to lack ofatmospheric density. A normal thermometer would readsignificantly below 0°C. This is due to the distancebetween the present molecules.

The MIR and International space stations havestable orbits within the upper part of the thermosphere,between 320 and 380 kilometers.

The Northern Lights also occur in the upperthermosphere.Thermopause

The Thermopause is the atmospheric boundary ofEarth’s energy system, located at the top of thethermosphere.

Below this, the atmosphere is defined to be activeon the insolation received, due to the increased presenceof heavier gases such as monoatomic oxygen.

The solar constant is thus expressed at the thermopause.Beyond (above) this, the exosphere describes the

thinnest remainder of atmospheric particles with largemean free path, mostly hydrogen and helium.

The exact altitude varies by the energy inputs oflocation, time of day, solar flux, season, etc. and can be between500-1000 km high at a given place and time. because ofthese,a portion of the magnetosphere dips below thislayer as well.

Althought these are all named layers of theatmosphere, the pressure is so negligible that the chiefly-used definitions of outer space are actually below thisaltitude.

Orbiting satellites do not experience significantatmospheric heating, but their orbits do decay over time,depending on orbital altitude. Space missions such asthe ISS, space shuttle, and Soyuz operate under this layer.

Atmosphere diagram showing the exosphere andother layers. The layers are not to scale: from Earth’ssurface to the top of the stratosphere (50km) is justunder 1% of Earth’s radius.The Exosphere

Exosphere is the uppermost layer of theatmosphere.

On Earth, its lower boundary at the edge of thethermosphere is estimated to be 500 km to 1000 kmabove the Earth’s surface, and its upper boundary atabout 10,000 km.

It is only from the exosphere that atmospheric gases,atoms, and molecules can, to any appreciable extent, escape into

outer space. The main gases within the exosphere arethe lightest gases, mainly hydrogen and helium, withsome atomic oxygen near the exobase.

The atmosphere in this layer is sufficientlyrarefied for satellites to orbit the Earth, although theystill receive some atmospheric drag.

Exobase, also called the critical level, the lowestaltitude of the exosphere, is defined in one of two ways:

The height above which there are negligibleatmospheric collisions between the particles and Theheight above which the constituent atoms are on purelyballistic trajectories.


CONCEPTS OF GEOGRAPHY EARLY HISTORY OF THE EARTH

Scientists believe the Earth began its life about 4.6billion years ago. The Earth formed as cosmic dust lumpedtogether to form larger and larger particles until 150 millionyears had passed. At about 4.4 billion years, the youngEarth had a mass similar to the mass it has today. Thecontinents probably began forming about 4.2 billion yearsago as the Earth continued to cool. The cooling alsoresulted in the release of gases from the lithosphere, muchof which formed the Earth’s early atmosphere. Most ofthe Earth’s early atmosphere was created in the first onemillion years after solidification (4.4 billion years ago).Carbon dioxide, nitrogen, and water vapor dominated thisearly atmosphere. Table below describes the three majorstages of development of the atmosphere

Evolution of the Earth’s atmosphereAs the Earth continued to cool, the water vapor

found in the atmosphere condensed to form the oceansand other fresh water bodies on the continents. Oxygenbegan accumulating in the atmosphere through photo-dissociation of 02 from water, and by way ofphotosynthesis. At about 450 million years ago, there wasenough oxygen in the atmosphere to allow for thedevelopment of a stratospheric ozone layer that was thickenough to keep terrestrial life protected from ultravioletradiation. As a result, terrestrial life began its developmentand expansion at this time.

Name of Stage Duration of Stage (Billions of Years Ago)

Main Constituents of the Atmosphere

Dominant Processes and Features

Early Atmosphere 4.4 to 4.0 H2O, hydrogen cyanide (HCN), ammonia (NH3), methane (CH4), sulfur, iodine, bromine, chlorine, argon

Lighter gases like hydrogen and helium escaped to space. All water was held in the atmosphere as vapor because of high temperatures.

Secondary Atmosphere

4.0 to 3.3 At 4.0 billion H2O, CO2, and nitrogen (N) dominant. Cooling of the atmosphere causes precipitation and the development of the oceans. By 3.0 billion CO2, H2O, N2 dominant. O2 begins to accumulate.

Continued release of gases from the lithosphere. Water vapor clouds common in the lower atmosphere. Chemosynthetic bacteria appear on the Earth at 3.6 billion. Life begins to modify the atmosphere.

Living Atmosphere 3.3 to Present N2 - 78%, O2 - 21%, Argon - 0.9%, CO2 - 0.036%

Development, evolution and growth of life increases the quantity of oxygen in the atmosphere from <1% to 21%. 500 million years ago concentration of atmospheric oxygen levels off. Humans begin modifying the concentrations of some gases in the atmosphere beginning around the year 1700.

The Natural Spheres:From the standpoint of Physical Geography, the

Earth can be seen to be composed of four principalcomponents:1) Lithosphere - describes the solid inorganic portion

of the Earth (composed of rocks, minerals andelements). It can be regarded as the outer surfaceand interior of the solid Earth. On the surface ofthe Earth, the lithosphere is composed of three maintypes of rocks:

2) Atmosphere - is the vast gaseous envelope of air thatsurrounds the Earth. Its boundaries are not easilydefined. The atmosphere contains a complex systemof gases and suspended particles that behave in many

Organism Group Time of Origin

Marine Invertebrates 570 Million Years Ago

Fish 505 Million Years Ago

Land Plants 438 Million Years Ago

Amphibians 408 Million Years Ago

Reptiles 320 Million Years Ago

Mammals 208 Million Years Ago

Flowering Plants 140 Million Years Ago

Approximate origin time of the major plant andanimal groups


CONCEPTS OF GEOGRAPHYways like fluids. Many of its constituents arederived from the Earth by way of chemical andbiochemical reactions.

3) Hydrosphere - describes the waters of the Earth(see the hydrologic cycle). Water exists on the Earthin various stores, including the atmosphere, oceans,lakes, rivers, soils, glaciers, and groundwater.

4) Biosphere - consists of all living things, plant andanimal. This zone is characterized by life in profusion,diversity, and ingenious complexity. Cycling of matterin this sphere involves not only metabolic reactionsin organisms, but also many abiotic chemical reactions.All of these spheres are interrelated to each other bydynamic interactions, like biogeochemical cycling,that move and exchange both matter and energybetween the four components.

Atmospheric CompositionNitrogen and oxygen are the main components of

the atmosphere by volume. Together these two gases makeup approximately 99 % of the dry atmosphere.

Nitrogen is removed from the atmosphere anddeposited at the Earth’s surface mainly by specializednitrogen fixing bacteria, and by way of lightning throughprecipitation. The addition of this nitrogen to the Earth’ssurface soils and various water bodies supplies much needednutrition for plant growth. Nitrogen returns to theatmosphere primarily through biomass combustion anddenitrification.

Oxygen is exchanged between the atmosphere and lifethrough the processes of photosynthesis and respiration.

Photosynthesis produces oxygen when carbon dioxideand water are chemically converted into glucose with thehelp of sunlight.

Respiration in humans and animals is a the opposite

process of photosynthesis. In respiration, oxygen iscombined with glucose to chemically release energy formetabolism. The products of this reaction are water andcarbon dioxide.

The next most abundant gas in the atmosphere iswater vapor

The highest concentrations of water vapor are foundnear the equator over the oceans and tropical rain forests.Water vapor has several very important functional roles onour planet:

• It redistributes heat energy on the Earth throughlatent heat energy exchange.

• The condensation of water vapor createsprecipitation that falls to the Earth’s surface providingneeded fresh water for plants and animals.

• It helps warm the Earth’s atmosphere through thegreenhouse effect.

The fifth most abundant gas in the atmosphere iscarbon dioxide. . The volume of this gas has increasedby over 25 % in the last three hundred years. This increaseis primarily due to human induced burning for fossil fuels,deforestation, and other forms of land-use change. Somescientists believe that this increase is causing globalwarming through an enhancement of the greenhouseeffect. Carbon dioxide is also exchanged between theatmosphere and life through the processes ofphotosynthesis and respiration.

Methane is a very strong greenhouse gas.The primarysources for the additional methane added to the atmosphere(in order of importance) are: rice cultivation; domesticgrazing animals; termites; landfills; coal mining; and, oil andgas extraction. Anaerobic conditions associated with ricepaddy flooding results in the formation of methane gas.Grazing animals release methane to the environment as aresult of herbaceous digestion.The Layered Atmosphere

The Earth’s atmosphere contains several differentlayers that can be defined according to air temperature.The atmosphere contains four different layers.Troposphere.

The first the layer is called troposphere.Depth of this layer varies from about 8 to 16

kilometers.Greatest depths occur at the tropics where warm

temperatures causes vertical expansion of the loweratmosphere.

From the tropics to the Earth’s polar regions thetroposphere becomes gradually thinner

The depth of this layer at the poles is roughly half asthick when compared to the tropics. Average depth of thetroposphere is approximately 11 kilometers as About 80% of the total mass of the atmosphere is contained introposphere.

It is also the layer where the majority of our weather

Gas Name Chemical Formula Percent Volume

Nitrogen N2 78.08%

Oxygen O2 20.95%

*Water H2O 0 to 4%

Argon Ar 0.93%

*Carbon Dioxide

CO2 0.0360%

Neon Ne 0.0018%

Helium He 0.0005%

*Methane CH4 0.00017%

Hydrogen H2 0.00005%

*Nitrous Oxide

N2O 0.00003%

*Ozone O3 0.000004%


CONCEPTS OF GEOGRAPHYoccurs Maximum air temperature also occurs near theEarth’s surface in this layer.

With increasing height, air temperature dropsuniformly with altitude at a rate of approximately 6.5°Celsius per 1000 meters. This phenomenon is commonlycalled the Environmental Lapse Rate.

At an average temperature of -56.5° Celsius, the topof the troposphere is reached. At the upper edge of thetroposphere is a narrow transition zone known as thetropopause.

Stratosphere: Above the tropopause is thestratosphere. This layer extends from an average altitudeof 11 to 50 kilometers above the Earth’s surface.

This stratosphere contains about 19.9 % of the totalmass found in the atmosphere. Very little weather occursin the stratosphere.

Occasionally, the top portions of thunderstormsbreach this layer. The lower portion of the stratosphere isalso influenced by the polar jet stream and subtropicaljet stream

In the first 9 kilometers of the stratosphere,temperature remains constant with height. A zone withconstant temperature in the atmosphere is called anisothermal layer

From an altitude of 20 to 50 kilometers, temperatureincreases with an increase in altitude. The highertemperatures found in this region of the stratosphereoccurs because of a localized concentration of ozone gasmolecules. These molecules absorb ultraviolet sunlightcreating heat energy that warms the stratosphere.

Ozone is primarily found in the atmosphere at varyingconcentrations between the altitudes of 10 to 50 kilometers.This layer of ozone is also called the ozone layer .

The ozone layer is important to organisms at theEarth’s surface as it protects them from the harmful effectsof the sun’s ultraviolet radiation. Without the ozone layerlife could not exist on the Earth’s surface.

Mesosphere: Separating the mesosphere from thestratosphere is transition zone called the stratopause. Inthe mesosphere, the atmosphere reaches its coldesttemperatures (about -90° Celsius) at a height ofapproximately 80 kilometers. At the top of the mesosphereis another transition zone known as the mesopause.

Thermosphere: The last atmospheric layer has analtitude greater than 80 kilometers and is called thethermosphere

Temperatures in this layer can be as high as 1200° C.These high temperatures are generated from the absorptionof intense solar radiation by oxygen molecules (O2).

The air in the thermosphere is extremely thin withindividual gas molecules being separated from each otherby large distances. Consequently, measuring the temperatureof thermosphere with a thermometer is a very difficultprocess.

Thermometers measure the temperature of bodies via

the movement of heat energy. Normally, this processtakes a few minutes for the conductive transfer of kineticenergy from countless molecules in the body of asubstance to the expanding liquid inside thethermometer. In the thermosphere, our thermometerwould lose more heat energy from radioactive emissionthen what it would gain from making occasional contactwith extremely hot gas molecules.The Ozone Layer

The ozone layer is a region of concentration of theozone molecule (O3) in the Earth’s atmosphere. The layersits at an altitude of about 10-50 kilometers, with amaximum concentration in the stratosphere at an altitudeof approximately 25 kilometers. In recent years, scientistshave measured a seasonal thinning of the ozone layerprimarily at the South Pole. This phenomenon is beingcalled the ozone hole.

The ozone layer naturally shields Earth’s life from theharmful effects of the sun’s ultraviolet (UV) radiation.A severe decrease in the concentration of ozone in theozone layer could lead to the following harmful effects:

An increase in the incidence of skin cancer(ultraviolet radiation can destroy acids in DNA).

A large increase in cataracts and sun burning.Suppression of immune systems in organisms.Adverse impact on crops and animals.Reduction in the growth of phytoplankton found in

the Earth’s oceans.Cooling of the Earth’s stratosphere and possibly some

surface climatic effect.Ozone is created naturally in the stratosphere by the

combining of atomic oxygen (O) with molecular oxygen(O2). This process is activated by sunlight. Ozone isdestroyed naturally by the absorption of ultravioletradiation,

O3 + UV >>> O2 + O and by the collision of ozonewith other atmospheric atoms and molecules.

O3 + O >>> 2O2

O3 + O3 >>> 3O2

Human activities are altering the amount ofstratospheric O3. The main agent responsible for thisdestruction was human-made chlorofluorocarbons orCFCs. First produced by General Motors Corporationin 1928, CFCs were created as a replacement to the toxicrefrigerant ammonia. CFCs have also been used as apropellant in spray cans, cleaner for electronics, sterilantfor hospital equipment, and to produce the bubbles inStyrofoam. CFCs are cheap to produce and are very stablecompounds, lasting up to 200 years in the atmosphere.By 1988, some 320,000 metric tons of CFCs were usedworldwide.Ozone depletion mechanism

CFCs created at the Earth’s surface drift slowly upwardto the stratosphere where ultraviolet radiation from the sun


CONCEPTS OF GEOGRAPHYcauses their decomposition and the release of chlorine(Cl). Chlorine in turn attacks the molecules of ozonechemically converting them into oxygen molecules

Cl + O3 >>> ClO + O2

ClO + O = Cl + O2

A single chlorine atom removes about 100,000 ozonemolecules before it is taken out of operation by othersubstances. Chlorine is removed from the stratosphere bytwo chemical reactions:

ClO + NO2 >>> ClONO2

CH4 + Cl >>> HCl + CH3

Normally, these two reactions would quickly neutralizethe chlorine released into the stratosphere. However, thepresence of polar stratospheric clouds, rich in nitrogen,and sunlight a series of reactions which prolongs thereactive life of chlorine in the atmosphere. Interestingly,these polar stratospheric clouds require very cold air(approximately -85° Celsius) for their formation.

Stratospheric air of this temperature occurs normallyevery year above Antarctica in the winter and early springmonths. Destruction of the ozone begins in Antarctica inthe spring as this region moves from 24 hours of night to24 hours of day. These clouds are less frequent in the Arcticstratosphere because winter cooling of the air in thestratosphere is less severe.Conservation

In 1987, a number of nations around the world metto begin formulating a global plan, known as the MontrealProtocol, to reduce and eliminate the use of CFCs.

Since 1987, the plan has been amended in 1990 and1992 to quicken the schedule of production andconsumption reductions. By 1996, 161 countries wereparticipating in the Protocol. The Montreal Protocol calledfor a 100 % reduction in the creation and use of CFCs byJanuary 1, 1996 in the world’s more developed countries.Less developed countries have until January 1, 2010 to stoptheir production and consumption of these dangerouschemicals.Atmospheric Pressure

Air is a tangible material substance and as a resulthas mass. Any object with mass is influenced by theuniversal force known as gravity. Gravity shapes andinfluences all atmospheric processes. It causes the densityand pressure of air to decrease exponentially as one movesaway from the surface of the Earth.Measuring Atmospheric Pressure

Any instrument that measures air pressure is calleda barometer.The most common type barometer used inhomes is the aneroid barometer.

For climatological and meteorological purposes,standard sea-level pressure is said to be 76.0 cm or 29.92inches or 1013.2 millibars. Scientists often use thekilopascal (kPa) as their preferred unit for measuringpressure. 1 kilopascal is equal to 10 millibars. Another

unit of force sometimes used by scientists to measureatmospheric pressure is the newton. One millibar equals100 newtons per square meter (N/m2).Atmospheric Pressure at the Earth’s Surface.

During the winter months (December to February),areas of high pressure develop over central Asia (SiberianHigh), off the coast California (Hawaiian High), centralNorth America (Canadian High), over Spain andnorthwest Africa extending into the subtropical NorthAtlantic (Azores High), and over the oceans in theSouthern Hemisphere at the subtropics. Areas of lowpressure occur just south of the Aleutian Islands (AleutianLow), at the southern tip of Greenland (Iceland Low),and latitudes 50 to 80° South.

During the summer months (June to August), anumber of dominant winter pressure systems disappear.Gone are the Siberian High over central Asia and thedominant low pressure systems near the Aleutian Islandsand at the southern tip of Greenland. The Hawaiian andAzores High intensify and expand northward into theirrelative ocean basins. High pressure systems over thesubtropical oceans in Southern Hemisphere also intensityand expand to the north. New areas of dominant highpressure develop over Australia and Antarctica (South PolarHigh). Regions of low-pressure form over central Asia andsouthwest Asia (Asiatic Low). These pressure systems areresponsible for the summer monsoon rains of Asia.Atmospheric Effects on Incoming Solar Radiation

Three atmospheric processes modify the solar radiationpassing through our atmosphere destined to the Earth’ssurface.a) Scattering

The process of scattering occurs when small particlesand gas molecules diffuse part of the incoming solarradiation in random directions without any alteration tothe wavelength of the electromagnetic energy.

Scattering does, however, reduce the amount ofincoming radiation reaching the Earth’s surface. Asignificant proportion of scattered short-wave solarradiation is redirected back to space.

The amount of scattering that takes place is dependenton two factors: wavelength of the incoming radiation andthe size of the scattering particle or gas molecule. In theEarth’s atmosphere, the presence of a large number ofparticles with a size of about 0.5 microns results in shorterwavelengths being preferentially scattered.

This factor also causes our sky to look blue becausethis color corresponds to those wavelengths that are bestdiffused. If scattering did not occur in our atmosphere thedaylight sky would be black.b) Absorption

If intercepted, some gases and particles in theatmosphere have the ability to absorb incominginsolation.

Absorption is defined as a process in which solar


CONCEPTS OF GEOGRAPHYradiation is retained by a substance and converted intoheat energy. The creation of heat energy also causesthe substance to emit its own radiation.

In general, the absorption of solar radiation bysubstances in the Earth’s atmosphere results in temperaturesthat get no higher than 1800° Celsius.

According to Wien’s Law, bodies with temperaturesat this level or lower would emit their radiation in the longwave band. Further, this emission of radiation is in alldirections so a sizable proportion of this energy is lost tospace.c) Reflection :

Reflection is a process where sunlight is redirect by180° after it strikes an atmospheric particle. This redirectioncauses a 100 % loss of the insolation.

Most of the reflection in our atmosphere occurs inclouds when light is intercepted by particles of liquid andfrozen water. The reflectivity of a cloud can range from40 to 90 %.

Sunlight reaching the Earth’s surface unmodified byany of the above atmospheric processes is termed directsolar radiation.

Solar radiation that reaches the Earth’s surface after itwas altered by the process of scattering is called diffusedsolar radiation.

Not all of the direct and diffused radiation availableat the Earth’s surface is used to do work (photosynthesis,creation of sensible heat, evaporation, etc.). As in theatmosphere, some of the radiation received at the Earth’ssurface is redirected back to space by reflection.

The reflectivity or albedo of the Earth’s surfacevaries with the type of material that covers it. For example,fresh snow can reflect up to 95 % of the insolation thatreaches it surface. Some other surface type reflectivities are:

Dry sand 35 to 45 %Broadleaf deciduous forest 5 to 10 %Needle leaf coniferous forest 10 to 20 %Grass type vegetation 15 to 25 %Reflectivity of the surface is often described by the

term surface albedo. The Earth’s average albedo,reflectance from both the atmosphere and the surface, isabout 30 %.

Global modification of incoming solar radiation byatmospheric and surface processes.Global Heat Balance:

Heat Fluxes: From 0 - 30° latitude North and Southincoming solar radiation exceeds outgoing terrestrialradiation and a surplusof energy exists. Thereverse holds true from30 - 90° latitude Northand South and theseregions have a deficit ofenergy.

Surplus energy at low latitudes and a deficit athigh latitudes results in energy transfer from the equatorto the poles. It is this meridional transport of energythat causes atmospheric and oceanic circulation.

If there were no energy transfer the poles wouldbe 25° Celsius.

The redistribution of energy across the Earth’ssurface is accomplished primarily through three processes:sensible heat flux, latent heat flux, and surface heatflux into oceans.

Sensible heat flux is the process where heat energyis transferred from the Earth’s surface to the atmosphereby conduction and convection. This energy is then movedfrom the tropics to the poles by advection, creatingatmospheric circulation. As a result, atmospheric circulationmoves warm tropical air to the Polar Regions and cold airfrom the poles to the equator.

Latent heat flux moves energy globally when solidand liquid water is converted into vapor. This vapor is oftenmoved by atmospheric circulation vertically and horizontallyto cooler locations where it is condensed as rain or isdeposited as snow releasing the heat energy stored withinit. Finally, large quantities of radiation energy are transferredinto the Earth’s tropical oceans. The energy enters thesewater bodies at the surface when absorbed radiation isconverted into heat energy. The warmed surface water isthen transferred downward into the water column byconduction and convection. Horizontal transfer of this heatenergy from the equator to the poles is accomplished byocean currents.

Surface energy: The following equation describes thepartitioning of heat energy at the Earth’s surface: Q* = H(Sensible heat) + L (Latent heat) + S (Surface heatflux into soil or water)

The Concept of atmospheric Temperature:Temperature ScalesA number of measurement scales have been invented

to measure temperature. The following TABLE describesimportant temperatures for the three dominant scales inuse today.

Temperature of absolute zero, the ice point of water,and the stream point of water using various temperaturemeasurement scales.Measurement Steam Point of Ice Point of AbsoluteScale Water Water ZeroFahrenheit 212 32 -460Celsius 100 0 -273Kelvin 373 273 0

The most commonly used scale for measuringtemperature is the Celsius system. The Celsius scale wasdeveloped in 1742 by the Swedish astronomer AndersCelsius. In this system, the melting point of ice wasgiven a value of 0, the boiling point of water is 100, and


CONCEPTS OF GEOGRAPHYabsolute zero is -273.

The Fahrenheit system is a temperature scale thatis used exclusively in the United States. This systemwas created by German physicist Gabriel Fahrenheit in1714. In this scale, the melting point of ice has a valueof 32, water boils at 212, and absolute zero has atemperature of -460.

The Kelvin scale was proposed by British physicistLord Kelvin in 1848. This system is often used by scientistsbecause its temperature readings begin at absolute zero anddue to the fact that this scale is proportional to the amountof heat energy found in an object. The Kelvin scale assignsa value of 273 for the melting temperature of ice, whilethe boiling point of water occurs at 373.Measurement of Air Temperature

A thermometer is a device that is used to measuretemperature.

Thermometers consist of a sealed hollow glass tubefilled with some type of liquid. Thermometers measuretemperature by the change in the volume of the liquidas it responds to the addition or loss of heat energyfrom the environment immediately outside its surface.

When heat is added, the liquid inside the thermometerexpands. Cooling cause the liquid to contract.

Meteorological thermometers are often filled witheither alcohol or mercury. Alcohol thermometers arefavored in very cold environments because of this liquid’slow freezing point (-112° Celsius).

By international agreement, the nations of the worldhave decided to measure temperature in a similar fashion.This standardization is important for the accurate generationof weather maps and forecasts, both of which depend onhaving data determined in a uniform way.

Temperature measurements are determined bythermometers designed and approved by the WorldMeteorological Organization, Geneva. These instrumentsare housed in specially designed instrument shelters thatallow for the standardization of measurements takenanywhere on the earth.

Daily and Annual Cycles of Global TemperatureDaily Cycles of Air Temperature

At the Earth’s surface quantities of insolation andnet radiation undergo daily cycles of change because theplanet rotates on its polar axis once every 24 hours.

Insolation is usually the main positive componentmaking up net radiation. Variations in net radiation areprimarily responsible for the particular patterns of risingand falling air temperature over a 24-hour period.Annual Cycle of Air Temperature

As the Earth revolves around the sun, locations onthe surface may under go seasonal changes in airtemperature because of annual variations in the intensityof net radiation.

Variations in net radiation are primarily controlled

by changes in the intensity and duration of receivedsolar insolation, which are driven by variations in daylength and angle of incidence.Global Surface Temperature Distribution

If the Earth was a homogeneous body without thepresent land/ocean distribution, its temperature distributionwould be strictly latitudinal as seen in the following figure.However, the Earth is more complex than this beingcomposed of a mosaic of land and water. This mosaiccauses latitudinal zonation of temperature to be disruptedspatially.

The following two factors are important in influencingthe distribution of temperature on the Earth’s surface:

The latitude of the location determines how muchsolar radiation is received. Latitude influences the angle ofincidence and duration of day length.

Surface properties - surfaces with high albedo absorbless incident radiation. In general, land absorbs lessinsolation that water because of its lighter color.

Even if two surfaces have the same albedo, a surface’sspecific heat determines the amount of heat energyrequired for a specific rise in temperature per unit mass.

The specific heat of water is some five times greaterthan that of rock and the land surface As a result, waterrequires the input of large amounts of energy to cause arise in its temperature

Substance Specific Heat Water 1.00 Air 0.24 Granite 0.19 Sand 0.19 Iron 0.11Mainly because of specific heat, land surfaces behave

quite differently from water surfaces. In general, the surfaceof any extensive deep body of water heats more slowlyand cools more slowly than the surface of a large landbody.

Other factors influencing the way land and watersurfaces heat and cool include:

Solar radiation warms an extensive layer in water onland just the immediate surface is heated. Water is easilymixed by the process of convection.

Evaporation of water removes energy from water’ssurface and substantially decreases it’s temperature.

Temperature distribution patterns for an averageJanuary and July

In January,Much of the terrestrial areas of the Northern

Hemisphere are below freezing. Some notable Northern Hemisphere cold-spots

include the area around Baffin Island Canada,Greenland, Siberia, and the Plateau of Tibet.


CONCEPTS OF GEOGRAPHYTemperatures over oceans tend to be hotter because ofthe water’s ability to hold heat energy.

In the Southern Hemisphere, temperatures over themajor landmasses are generally greater than 20° Celsius withlocalized hot spots in west-central Australia, the KalahariDesert in Africa, and the plains of Bolivia, Paraguay, andArgentina. Subtropical oceans are often warmer thanlandmass areas near the equator.

At this latitude, land areas receive less incoming solarradiation because of the daily convective development ofcumulus and cumulonimbus clouds.

In the mid-latitudes, oceans are often cooler thanlandmass areas at similar latitudes. Terrestrial areas arewarmer because of the rapid heating of land surfaces underfrequently clear skies.

Antarctica remains cold and below zero degreesCelsius due to the presence of permanent glacial ice whichreflects much of the solar radiation received back to space.

In July, The Northern Hemisphere is experiencing its summer

season because the North Pole is now tilted towards thesun.

Some conspicuous hot spots include the south-centralUnited States, Arizona and northwest Mexico, northernAfrica, the Middle East, India, Pakistan, and Afghanistan.

Temperature over oceans tend to be relatively coolerbecause of the land’s ability to heat quickly. Two terrestrialareas of cooler temperatures include Greenland and thePlateau of Tibet. In these regions, most of the incomingsolar radiation is sent back to space because of the presenceof reflective ice and snow.

In the Southern Hemisphere, temperatures over themajor landmasses are generally cooler than ocean surfacesat the same latitude.

Antarctica is bitterly cold because it is experiencingtotal darkness. Note that Antarctica is much colder thanthe Arctic was during its winter season.

The Arctic consists mainly of ocean. During thesummer, this surface is able to absorb considerablequantities of sunlight, which is then converted into heatenergy. The heat stored in the ocean is carried over intothe winter season.

Antarctica has a surface composed primarily of snowand ice. This surface absorbs only a small amount of thesolar radiation during the summer. So it never really heatsup. As a result, the amount of heat energy stored into thewinter season is minimal.Forces Acting to Create Wind

Wind can be defined simply as air in motion. Thismotion can be in any direction, but in most cases thehorizontal component of wind flow greatly exceeds theflow that occurs vertically.

Wind develops as a result of spatial differences inatmospheric pressure. Generally, these differences occur

because of uneven absorption of solar radiation at theEarth’s surface . Wind speed tends to be at its greatestduring the daytime when the greatest spatial extremes inatmospheric temperature and pressure exist

Formation of wind as a result of localizedtemperature differences.

Wind is often described by two characteristics:Wind speed and wind direction.

Wind speed is the velocity attained by a mass of airtraveling horizontally through the atmosphere. Wind speedis often measured with an anemometer in kilometers perhour (kmph), miles per hour (mph), knots, or meters persecond (mps).

Wind direction is measured as the direction fromwhere a wind comes from. For example, a southerly windcomes from the south and blows to the north. Directionis measured by an instrument called a wind vane.

Both of these instruments are positioned in theatmospheric environment at a standard distance of 10meters above the ground surface.

Wind speed can also be measured without the aidof instruments using the Beaufort wind scale. Thisdescriptive scale was originally developed by Admiral Beaufortof the British Navy in the first decade of the 17th century.

The purpose for this system was to allow mariners todetermine wind speed from simple observations. TheBeaufort system has undergone several modifications tostandardize its measurement scale and to allow for its useon land.

Users of this scale look for specific effects of thewind on the environment to determine speed.

Winds are named according to the compass directionof their source. Thus, a wind from the north blowingtoward the south is called a northerly wind. FollowingFigure describes the sixteen principal bearings of winddirection. Most meteorological observations report winddirection using one of these sixteen bearings

*Wind compass describing the sixteen principalbearings used to measure wind direction. This compass isbased on the 360 degrees found in a circle.



Horizontally, at the Earth’s surface wind alwaysblows from areas of high pressure to areas of lowpressure (vertically, winds move from areas of lowpressure to areas of high pressure), usually at speedsdetermined by the rate of air pressure change betweenpressure centers.

This situation is comparable to someone skiing downa hill. The skier will of course move from the top of thehill to the bottom of the hill, with the speed of theirdescent controlled by the gradient or steepness of the slope.Likewise, wind speed is a function of the steepness orgradient of atmospheric air pressure found between highand low pressure systems.

When expressed scientifically, pressure change over aunit distance is called pressure gradient force, and thegreater this forces the faster the winds will blow.

On weather maps, pressure is indicated by drawingisolines of pressure, called isobars, at regular 4 millibarintervals (e.g., 996 mb, 1000 mb, 1004 mb, etc.).

If the isobars are closely spaced, we can expect thepressure gradient force to be great, and wind speed to behigh.

In areas where the isobars are spaced widely apart,the pressure gradient is low and light winds normally exist.Driving Forces of wind

Wind is the result of a limited number ofaccelerating and decelerating forces, and that the actionof these forces is controlled by specific fundamental naturallaws.

Sir Isaac Newton formulated these laws as severallaws of motion. The first law suggests that an objectthat is stationary will remain stationary, and an objectin motion will stay in motion as long as no opposingforce is put on the object..

Newton’s second law of motion suggests that theforce put on an object equals its mass multiplied by the

acceleration produced. The term force in this law refersto the total or net effect of all the forces acting on anobject. Mathematically, this law is written as:

Force = Mass x AccelerationOrAcceleration = Force/MassFrom this natural law of motion we can see that the

acceleration of an object is directly proportional to the netforce pushing or pulling that body and inverselyproportional to the mass of the body.

Pressure gradient force is the primary forceinfluencing the formation of wind from local to globalscales. This force is determined by the spatial pattern ofatmospheric pressure at any given moment in time.

The diagram displays the relative relationshipbetween pressure gradient and wind speed. Thisrelationship is linear and positive. As a result,

quadrupling the pressure gradient increases wind speedby a factor of four. This is what we would expectaccording to Newton’s second law of motion, assumingthe mass of the wind is unchanged.

Coriolis force: The rotation of the Earth createsanother force, termed Coriolis force, which acts upon windand other objects in motion in very predictable ways.According to Newton’s first law of motion, air willremain moving in a straight line unless it is influencedby an unbalancing force. The consequence of Coriolisforce opposing pressure gradient acceleration is that themoving air changes direction.

Instead of wind blowing directly from high to lowpressure, the rotation of the Earth causes wind to bedeflected off course.

In the Northern Hemisphere, wind is deflectedto the right of its path, while in the SouthernHemisphere it is deflected to the left.

However the magnitude of the Coriolis force varieswith the velocity and the latitude of the object.

Coriolis force is absent at the equator, and its strengthincreases as one approaches either pole. Furthermore,an increase in wind speed also results in a strongerCoriolis force, and thus in greater deflection of the


CONCEPTS OF GEOGRAPHYwind.

Coriolis force only acts on air when it has been sentinto motion by pressure gradient force. Finally, Coriolisforce only influences wind direction and never windspeed

Centripetal acceleration is the force that can act onmoving air. It acts only on air that is flowing around centersof circulation.

Centripetal acceleration is also another force that caninfluence the direction of wind. Centripetal accelerationcreates a force directed at right angles to the flow of thewind and inwards towards the centers of rotation (e.g., lowand high pressure centers).

This force produces a circular pattern of flow aroundcenters of high and low pressure.

Centripetal acceleration is much more important forcirculations smaller than the mid-latitude cyclone.

The other force that can influence moving air isfrictional deceleration. Friction can exert an influence onwind only after the air is in motion.

Frictional drag acts in a direction opposite to the pathof motion causing the moving air to decelerate (Accordingto Newton’s first and second laws of motion). Frictionaleffects are limited to the lower one kilometer above theEarth’s surface.Geotropic Wind

Air under the influence of both the pressure gradientforce and Coriolis force tends to move parallel to isobarsin conditions where friction is low (1000 meters above thesurface of the Earth) and isobars are straight. Winds ofthis type are usually called geostrophic winds.

Geostrophic winds come about because pressuregradient force and Coriolis force come into balance afterthe air begins to move.

A geostrophic wind flows parallel to the isobars. Inthis model of wind flow in the Northern Hemisphere, windbegins as a flow of air perpendicular to the isobars(measured in millibars) under the primary influence ofthe pressure gradient force (PGF).

As the movement begins, the Coriolis force (CF)begins to influence the moving air causing it to deflect tothe right of its path. This deflection continues until thepressure gradient force and Coriolis force are oppositeand in balance with each other.

Finally, Buy Ballot’s Law states that when you standwith your back to a geotropic wind in the NorthernHemisphere the center of low pressure will be to your leftand the high pressure to your right. The opposite is truefor the Southern Hemisphere.Gradient Wind

Wind above the Earth’s surface does not always travelin straight lines. In many cases winds flow around thecurved isobars of a high (anticyclone) or low (cyclone)pressure center. A wind that blows around curved

isobars above the level of friction is called a gradientwind.

Gradient winds are slightly more complex thangeotropic winds because they include the action of yetanother physical force. This force is known as centripetalforce and it is always directed toward the center of rotation.

Around a low, the gradient wind consists of thepressure gradient force and centripetal force actingtoward the center of rotation, while Coriolis force actsaway from the center of the low.

In a high pressure center, the Coriolis and centripetalforces are directed toward the center of the high, whilethe pressure gradient force is directed outward.

The following figure describes the forces thatproduce gradient winds around high and low pressurecenters

Circulation patterns of high and low pressuresystems in the North and South Hemisphere.

Local and Regional Wind SystemsWinds blow because of differences in atmospheric

pressure. Pressure gradients may develop on a local toa global scale because of differences in the heating andcooling of the Earth’s surface. Heating and cooling cyclesthat develop daily or annually can create several commonlocal or regional thermal wind systems.

Sea and Land BreezesSea and land breezes are types of thermal

circulation systems that develop at the interface of landand ocean.

At this interface, the dissimilar heating and coolingcharacteristics of land and water initiate the developmentof an atmospheric pressure gradient, which causes the airin these areas to flow.

During the daytime land heats up much faster thanwater as it receives solar radiation from the sun. Thewarmer air over the land then begins to expand and riseforming a thermal low.

At the same time, the air over the ocean becomes acool high because of water’s slower rate of heating.

Air begins to flow as soon as there is a significantdifference in air temperature and pressure across the


CONCEPTS OF GEOGRAPHYland to sea gradient.

The development of this pressure gradient causes theheavier cooler air over the ocean to move toward the landand to replace the air rising in the thermal low.

This localized airflow system is called a sea breeze. Sea breeze usually begins in midmorning and reaches

its maximum strength in the later afternoon when thegreatest temperature and pressure contrasts exist. It diesdown at sunset when air temperature and pressure onceagain become similar across the two surfaces.

At sunset, the land surface stops receiving radiationfrom the sun. As night continues the land surface beginslosing heat energy at a much faster rate than the watersurface. After a few hours, air temperature and pressurecontrasts begin to develop between the land and oceansurfaces.

The land surface being cooler than the water becomesa thermal high-pressure area. The ocean becomes a warmthermal low. Wind flow now moves from the land to theopen ocean. This type of localized air flow is called a landbreezeMountain and Valley Breezes

Mountain and valley breezes are common in regionswith great topographic relief.

A valley breeze develops during the day as the sunheats the land surface and air at the valley bottom andsides. As the air heats it becomes less dense and buoyantand begins to flow gently up the valley sides. Vertical ascentof the air rising along the sides of the mountain is usuallylimited by the presence of a temperature inversion layer.When the ascending air currents encounter the inversionthey are forced to move horizontally and then back downto the valley floor. This creates a self-contained circulationsystem.

If conditions are right, the rising air can condenseand form into cumuliform clouds. During the night, theair along the mountain slopes begins to cool quickly becauseof long wave radiation loss. As the air cools, it becomesmore dense and begins to flow down slope causing amountain breeze. Convergence of the draining air occursat the valley floor and forces the air to move verticallyupward. The upward movement is usually limited by thepresence of a temperature inversion, which forces theair to begin moving horizontally. This horizontal movementcompletes the circulation cell system.

In narrowing terrain, mountain winds can acceleratein speed because of the venturi effect. Such winds canattain speeds as high has 150 kilometers per hour.Monsoon Winds

Monsoons are regional scale wind systems thatpredictably change direction with the passing of the seasons.Like land/sea breezes, these wind systems are created bythe temperature contrasts that exist between the surfacesof land and ocean. However, monsoons are differentfrom land/sea breezes both spatially and temporally.

Monsoons occur over distances of thousands ofkilometers, and their two dominant patterns of wind flowact over an annual time scale.

During the summer, monsoon winds blow from thecooler ocean surfaces onto the warmer continents.

In the summer, the continents become much warmerthan the oceans because of a number of factors.

These factors include:Specific heat differences between land and water.Greater evaporation over water surfaces.Subsurface mixing in ocean basins, which

redistributes heat energy through a deeper layer.Precipitation is normally associated with the summer

monsoons. Onshore winds blowing inland from the warmocean are very high in humidity, and slight cooling of theseair masses causes condensation and rain.

In some cases, this precipitation can be greatlyintensified by orographic uplift(Mountain elevations).Some highland areas in Asia receive more than 10 metersof rain during the summer months.

In the winter, the wind patterns reverse, as the oceansurfaces are now warmer. With little solar energy available,the continents begin cooling rapidly as long wave radiationis emitted to space. The ocean surface retains its heatenergy longer because of water’s high specific heat andsubsurface mixing. The winter monsoons bring cleardry weather and winds that flow from land to sea.

Atmospheric CirculationPlanetary rotation would cause the development

of three circulation cells in each hemisphere rather thanone. These three circulation cells are known as the:Hadley cell; Ferrell cell; and Polar cell.

In this circulation pattern, the equator remains thewarmest location on the Earth. This area of greater heatacts as zone of thermal lows known as the intertropicalconvergence zone (ITCZ).

The Intertropical Convergence Zone draws in surfaceair from the subtropics. When this subtropical air reachesthe equator, it rises into the upper atmosphere because ofconvergence and convection.

It attains a maximum vertical altitude of about 14kilometers (top of the troposphere), and then beginsflowing horizontally to the North and South Poles. Coriolisforce causes the deflection of this moving air in the upperatmosphere, and by about 30° of latitude the air begins toflow zonally from west to east. This zonal flow is knownas the subtropical jet stream.

The zonal flow also causes the accumulation of air inthe upper atmosphere as it is no longer flowingmeridionally. To compensate for this accumulation, someof the air in the upper atmosphere sinks back to thesurface creating the subtropical high pressure zone.

From this zone, the surface air travels in two


CONCEPTS OF GEOGRAPHYdirections. A portion of the air moves back toward theequator completing the circulation system known as the

Hadley cell.This moving air is also deflected by the Coriolis

effect to create the Northeast Trades (right deflection)and Southeast Trades (left deflection).

The surface air moving towards the poles from thesubtropical high zone is also deflected by Coriolisacceleration producing the Westerlies. Between the latitudesof 30 to 60° North and South, upper air winds blowgenerally towards the poles.

Once again, Coriolis force deflects this wind tocause it to flow west to east forming the polar jet streamat roughly 60° North and South.

On the Earth’s surface at 60° North and Southlatitude, the subtropical Westerlies collide with coldair traveling from the poles. This collision results infrontal uplift and the creation of the sub polar lows ormid-latitude cyclones.

A small portion of this lifted air is sent back intothe Ferrell cell after it reaches the top of thetroposphere. Most of this lifted air is directed to thepolar vortex where it moves downward to create thepolar high.Actual Global Surface Circulation

The circulation patterns are seen differ somewhatfrom the three-cell model particularly in recent past.The actual surface circulation for the Earth asdetermined from 39 years of record is as follows.

These differences are caused primarily by twofactors. First, the Earth’s surface is not composed ofuniform materials. The two surface materials thatdominate are water and land. These two materialsbehave differently in terms of heating and coolingcausing latitudinal pressure zones to be less uniform.

The other factor influencing actual circulation patternsis elevation. Elevation tends to cause pressure centers tobecome intensified when altitude is increased. This isespecially true of high-pressure systems

The formation of intertropical convergence zone isthe result of solar heating and the convergence of thetrade winds

In January, the intertropical convergence zone is

found south of the equator. During this time period,the Southern Hemisphere is tilted towards the sun and

receives higher inputs of short-wave radiation..During July, the intertropical convergence

zone (ITCZ) is generally found north of theequator. This shift in position occurs because thealtitude of the sun is now higher in the NorthernHemisphere.

The more intense July sun causes land areasof Northern Africa and Asia rapidly warmcreating the Asiatic Low, which becomes part ofthe ITCZ.

In the winter months, the intertropicalconvergence zone is pushed south by the developmentof an intense high-pressure system over central Asia.The extreme movement of the ITCZ in this part of theworld also helps to intensify the development of aregional winds system called the Asian monsoon.

The subtropical high-pressure zone does not forma uniform area of high pressure stretching around the worldin reality. Instead, the system consists of several localizedanticyclonic cells of high pressure.

These systems are located roughly at about 20 to 30°of latitude. The subtropical high-pressure systems developbecause of the presence of descending air currents fromthe Hadley cell.

These systems intensify over the ocean during thesummer or high sun season. During this season, the airover the ocean bodies remains relatively cool because ofthe slower heating of water relative to land surfaces. Overland, intensification takes place in the winter months. Atthis time, land cools off quickly, relative to ocean, forminglarge cold continental air masses.

The sub polar lows form a continuous zone of lowpressure in the Southern Hemisphere at a latitude ofbetween 50 and 70°.

The intensity of the sub polar lows varies withseason.

This zone is most intense during SouthernHemisphere summer At this time, greater differences intemperature exist between air masses found either side ofthis zone.

North of sub polar low belt, summer heating warmssubtropical air masses. South of the zone, the ice-coveredsurface of Antarctica reflects much of the incoming solarradiation back to space. As a consequence, air massesabove Antarctica remain cold because very little heating ofthe ground surface takes place. The meeting of the warmsubtropical and cold polar air masses at the sub polar lowzone enhances frontal uplift and the formation of intenselow-pressure systems.

In the Northern Hemisphere, the sub polar lows donot form a continuous belt circling the globe. Instead,they exist as localized cyclonic centers of low pressure.

In the Northern Hemisphere winter, these


CONCEPTS OF GEOGRAPHYpressure centers are intense and located over the oceansjust to the south of Greenland and the Aleutian Islands.

These areas of low pressure are responsible forspawning many mid-latitude cyclones.

The development of the sub polar lows in summeronly occurs weakly over Greenland and Baffin Island,Canada), unlike the Southern Hemisphere. The reason forthis phenomenon is that considerable heating of the Earth’ssurface occurs from 60 to 90° North. As a result, coldpolar air masses generally do not form.

Upper Air Winds and the Jet StreamsThe polar jet stream is formed by the deflection of

upper air winds by coriolis acceleration. It resembles a stream of water moving west to east

and has an altitude of about 10 kilometers. Its airflow is intensified by the strong temperature

and pressure gradient that develops when cold air fromthe poles meets warm air from the tropics.

Wind velocity is highest in the core of the polar jetstream where speeds can be as high as 300 kilometers perhour.

The jet stream core is surrounded by slower movingair that has an average velocity of 130 kilometers per hourin winter and 65 kilometers per hour in summer.

Polar front: Associated with the polar jet stream isthe polar front. At this zone, massive exchanges ofenergy occur in the form of storms known as the mid-latitude cyclones.

The shape and position of waves in the polar jetstream determine the location and the intensity of the mid-latitude cyclones.

In general, mid-latitude cyclones form beneath polarjet stream troughs.

The subtropical jet stream is located approximately13 kilometers above the subtropical high-pressure zone.

THE DAILY PRESSURE LEVELSThe most basic change in pressure is the twice

daily rise and fall in due to the heating from the sun.Each day, around 4 a.m./p.m. the pressure is at itslowest and near its peak around 10 a.m./p.m. Themagnitude of the daily cycle are greatest near theequator decreasing toward the poles.

On top of the daily fluctuations are the largerpressure changes as a result of the migrating weathersystems. These weather systems are identified by theblue H’s and red L’s seen on weather maps. The H’srepresent the location of the area of highest pressure.The L’s represent the position of the lowest pressure.

The FALL of the barometer (decreasing pressure)In very hot weather, the fall of the barometer

denotes thunder. Otherwise, the sudden falling of thebarometer denotes high wind. In frosty weather, the fallof the barometer denotes thaw.

If wet weather happens soon after the fall of thebarometer, expect but little of it.

In wet weather if the barometer falls expect muchwet.

In fair weather, if the barometer falls much andremains low, expect much wet in a few days, andprobably wind.

The barometer sinks lowest of all for wind andrain together; next to that wind, (except it be an east ornorth-east wind).

The RISE of the barometer (increasing pressure)In winter, the rise of the barometer presages frost.In frosty weather, the rise of the barometer presages

snow If fair weather happens soon after the rise of thebarometer, expect but little of it.

In wet weather, if the mercury rises high andremains so, expect continued fine weather in a day ortwo.

In wet weather, if the mercury rises suddenly veryhigh, fine weather will not last long.

The barometer rises highest of all for north andeast winds; for all other winds it sinks.

The barometer UNSETTLED (unsteady pressure)If the motion of the mercury be unsettled, expect

unsettled weather.If it stand at “MUCH RAIN” and rises to

“CHANGEABLE” expect fair weather of shortcontinuance.

If it stand at “FAIR” and fall to “CHANGEABLE”,expect foul weather.

Its motion upwards, indicates the approach of fineweather; its motion downwards, indicates the approachof foul weather.

These pressure observations hold true for manyother locations as well but not all of them. Storms thatoccur in England, located near the end of the GulfStream, bring large pressure changes. In the UnitedStates, the largest pressure changes associated withstorms will generally occur in Alaska and northern halfof the continental U.S. In the tropics, except for tropicalcyclones, there is very little day-to-day pressure changeand none of the rules apply.


CONCEPTS OF GEOGRAPHYTHE HYDROSPHERE

The Hydrologic Cycle:The hydrologic cycle is a conceptual model that

describes the storage and movement Water moves fromone reservoir to another by way of processes likeevaporation, condensation, precipitation, deposition,runoff, infiltration, sublimation, transpiration, melting,and groundwater flow.

The oceans supply most of the evaporated waterfound in the atmosphere. Of this evaporated water, only91 % of it is returned to the ocean basins by way ofprecipitation.

The remaining 9 % is transported to areas overlandmasses where climatological factors induce theformation of precipitation.

The resulting imbalance between rates of evaporationand precipitation over land and ocean is corrected by runoffand groundwater flow to the oceans.

The planetary water supply is dominated by the oceans.Approximately 97 % of all the water on the Earth is inthe oceans. The other 3 % is held as freshwater in glaciersand icecaps, groundwater, lakes, soil, the atmosphere, andwithin life.

Water is continually cycled between its variousreservoirs. This cycling occurs through the processes ofevaporation, condensation, precipitation, deposition,runoff, infiltration, sublimation, transpiration, melting,and groundwater flow.

On average water is renewed in rivers once every 16days.

Water in the atmosphere is completely replaced onceevery 8 days.

Slower rates of replacement occur in large lakes,glaciers, ocean bodies and groundwater.

Replacement in these reservoirs can take fromhundreds to thousands of years.

Some of these resources (especially groundwater) arebeing used by humans at rates that far exceed their renewaltimes.

This type of resource use is making this type of water

effectively nonrenewable.Reservoir Average Residence Time Glaciers 20 to 100 years Seasonal Snow Cover 2 to 6 months Soil Moisture 1 to 2 months Groundwater: Shallow 100 to 200 years Groundwater: Deep 10,000 years Lakes 50 to 100 years Rivers 2 to 6 mAtmospheric Humidity:

The water vapor CONTENT of the atmosphere iscalled Humidity.

The amount of humidity found in air varies becauseof a number of factors. Two important factors areevaporation and condensation.

At the water/atmosphere interface over our planet’soceans large amounts of liquid water are evaporated intoatmospheric water vapor. This process is mainly caused byabsorption of solar radiation and the subsequent generationof heat at the ocean’s surface.

In our atmosphere, water vapor is converted backinto liquid form when air masses lose heat energy and cool.This process is responsible for the development of mostclouds and also produces the rain that falls to the Earth’ssurface.

Scientists have developed a number of differentmeasures of atmospheric humidity such as mixing ratio,saturation mixing ratio, and relative humidity.

Mixing ratio is a measure that refers to the massof a specific gas component relative to the mass of theremaining gaseous components for a sample of air.

When used to measure humidity mixing ratio wouldmeasure the mass of water vapor relative to the mass ofall of the other gases.

In meteorological measurements, mixing ratio isusually expressed in grams of water vapor per kilogramof dry air.

Saturation mixing ratio refers to the mass of watervapor that can be held in a kilogram of dry air at saturation.

Saturation can be generally defined as the conditionwhere any addition of water vapor to a mass of air leads

to the condensation of liquid water or the deposition ofice at a given temperature and pressure.

The warmer air has a higher saturation-mixing ratiothan cooler air at a constant atmospheric pressure. It is


CONCEPTS OF GEOGRAPHYimportant to note that this relationship betweentemperature and water vapor content in the air is notlinear but exponential.

In other words, for each 10° increase in temperature,saturation mixing ratio increases by a larger quantity.

The most commonly used measure of humidity isrelative humidity.

Relative humidity can be simply defined as theamount of water in the air relative to the saturation amountthe air can hold at a given temperature multiplied by 100.

Air with a relative humidity of 50 % contains a halfof the water vapor it could hold at a particular temperature.

The following illustration describes how relativehumidity changes in a parcel of air with an increase in airtemperature. At 10° Celsius, a parcel of dry air weighingone kilogram can hold a maximum of 7.76 grams of watervapor. In this state, the parcel of air would be at saturationand its relative humidity would be 100 %. Increasing thetemperature of this parcel, without adding or removing anywater, would increase its ability to hold water vapor.According to Table, a 10 degree Celsius rise in temperaturewould increase the saturation-mixing ratio of this parcelof air to 14.85 grams. Since no water has been added orremoved, the actual amount of water in the parcel wouldremain 7.76 grams. This quantity is known as the mixingratio. Dividing the mixing ratio by the saturation mixingratio and then multiplying this number by 100 determinesthe relative humidity of the parcel of air (7.76/14.85 x100 = 52 %). At a temperature of 20° Celsius, relativehumidity would be 52 %. Raising the temperature of theparcel of air by another 10° Celsius would again lower itsrelative humidity. In this state, the actual mixing ratio wouldstill be 7.76 grams, while the saturation mixing ratio wouldincrease to 27.69 grams. Relative humidity would drop to28 % at a temperature of 30° Celsius (7.76/27.69 x 100 =28 %).Measuring Humidity

Humidity can be measured using a variety ofinstruments. Relative humidity is often determined using asling psychrometer or a hair hygrometer.

A sling psychrometer is a device that consists oftwo thermometers joined to a piece of plastic or metal.One of the thermometers, called the wet-bulbthermometer, has small cloth hood (wick) that is pulledover the reservoir bulb. The other thermometer has nohood and is called the dry-bulb thermometer.

Hair hygrometers work on the fact that hair changesits length when humidity varies. This device usually consistsof a number of human or horse hairs connected to amechanical lever system. When humidity increases thelength of the hairs becomes longer. This change in lengthis then transmitted and magnified by the lever system intoa measurement of relative humidity.

Humidity is also measured on a global scale usingremotely placed satellites. These satellites are able to detect

the concentration of water in the troposphere ataltitudes between 4 and 12 kilometers. Satellites that canmeasure water vapor have sensors that are sensitive toinfrared radiation. Water vapor specifically absorbs andre-radiates radiation in this spectral band. Satellite watervapor imagery plays an important role in monitoringclimate conditions (like the formation ofthunderstorms) and in the development of futureweather forecasts. Dew Point and Frost Point

Associated with relative humidity is dew point (ifthe dew point is below freezing, it is referred to as thefrost point). Dew point is the temperature at whichwater vapor saturates from an air mass into liquid orsolid usually forming rain, snow, frost, or dew.

Dew point normally occurs when a mass of airhas a relative humidity of 100 %. This happens in theatmosphere as a result of cooling through a number ofdifferent processes.Condensation, Freezing, and Deposition

The three processes of phase change of waterwithin the atmosphere are:

Condensation - water moving from a vapor to aliquid state.

Freezing - water moving from a liquid to a solidstate.

Deposition - water moving from a vapor to a solidstate.

For a phase change to occur heat energy must beadded to or removed from water molecules.

The formation of water droplets and ice crystalstakes place when the water in the atmosphere is cooled.As air containing water vapor cools, the relativehumidity of the air parcel increases until the dew orfrost point is reached.

At dew point (relative humidity = 100 %) waterbegins to condense into droplets. If 100 % relativehumidity is reached below 0° Celsius deposition occursand ice crystals form.

Formation of water droplets and ice crystals alsorequires a surface for condensation, freezing, ordeposition. In the atmosphere, these surfaces aremicroscopic particles of dust, smoke, and salt commonlycalled condensation nuclei.

Deposition nuclei, six sided particles, are neededfor the formation of ice crystals.

If there is a deficiency of nuclei, super-saturationcan result and condensation, freezing, or deposition canonly occur with a relative humidity that is greater than100 %Cloud Formation Processes

Condensation or deposition of water above theEarth’s surface creates clouds.


CONCEPTS OF GEOGRAPHYIn general, clouds develop in any air mass that

becomes saturated (relative humidity becomes 100 %).Saturation can occur by way of atmospheric mechanismsthat cause the temperature of an air mass to be cooled toits dew point or frost point.

The following mechanisms or processes can achievethis outcome causing clouds to develop:(1). Orographic uplift occurs when air is forced to rise

because of the physical presence of elevated land. Asthe parcel raises it cools as a result of adiabaticexpansion at a rate of approximately 10° Celsius per1000 meters until saturation. The development ofclouds and resulting heavy quantities of precipitationalong the west coast of Canada are mainly due tothis process.

(2). Convectional lifting is associated with surface heatingof the air at the ground surface. If enough heatingoccurs, the mass of air becomes warmer and lighterthan the air in the surrounding environment, and justlike a hot air balloon it begins to rise, expand, andcool. When sufficient cooling has taken placesaturation occurs forming clouds. This process isactive in the interior of continents and near theequator forming cumulus clouds and orcumulonimbus clouds (thunderstorms). The rain thatis associated with the development of thunderstormclouds is delivered in large amounts over short periodsof time in extremely localized areas.

(3). Convergence or frontal lifting takes place when twomasses of air come together. In most cases, the twoair masses have different temperature and moisturecharacteristics. One of the air masses is usually warmand moist, while the other is cold and dry. The leadingedge of the latter air mass acts as an inclined wall orfront causing the moist warm air to be lifted. Ofcourse the lifting causes the warm moist air mass tocool due to expansion resulting in saturation. Thiscloud formation mechanism is common at the mid-latitudes where cyclones form along the polar frontand near the equator where the trade winds meet atthe intertropical convergence zone.

(4). Radiative cooling occurs when the sun is no longersupplying the ground and overlying air with energyderived from solar insolation (e.g., night). Instead, thesurface of the Earth now begins to lose energy in theform of long wave radiation, which causes the groundand air above it to cool. The clouds that result fromthis type of cooling take the form of surface fog.These causes of cloud development do not always act

in a singular fashion. It is possible to get combinations ofall four types, such as when convection and orographicuplift cause summer afternoon cloud development andshowers in the mountains.Precipitation and Fog

Precipitation can be defined as any liquid or solid

aqueous deposit that forms in a saturated atmosphere(relative humidity equals 100 %) and falls from clouds tothe ground surface.

A necessary initial requirement for this process isthe presence of both condensation nuclei and depositionnuclei. While deposition nuclei form ice crystals attemperatures just below zero degrees Celsius,condensation nuclei can remain liquid (super cooled)to temperatures as low as -40° Celsius depending onsize. Because of this phenomenon, cold clouds cancontain both ice crystals and super cooled waterdroplets.

The relative proportion of these two types ofparticles determines whether snow crystals grow to a sizeto overcome atmospheric updrafts.

The following list describes the various types ofprecipitation that can form in the atmosphere:

Rain is any liquid deposit that falls from theatmosphere to the surface and has a diameter greater than0.5 millimeters. The maximum size of a raindrop is about5 millimeters. Beyond this size inter-molecular cohesiveforces become too weak to hold the mass of water togetheras a single drop.

Freezing rain takes place when falling liquid waterdroplets encounter a surface with a temperature below 0°Celsius. Upon contact with this surface, the rain quicklyturns into ice. Another important condition required forfreezing rain is that the atmosphere where rain developsmust be above freezing. A situation where warm air is foundon top of cold air is called a temperature inversion.Temperature inversions are not the common state of thelower atmosphere. Usually, air temperature decreases withan increase in altitude in the troposphere. In the mid-latitudes, we often find temperature inversions developingalong the moving front edge of a cold air mass that isovertaking warmer air. This condition causes the less densewarm air to be pushed up and over the more dense coldair.

Ice pellets or sleet are transparent or translucentspheres of frozen water. They have a diameter smaller than5 millimeters. This form of precipitation develops firstas raindrops in a relatively warm atmosphere wherethe temperature is above freezing. These raindrops thendescend into a colder lower layer of the atmospherewhere freezing temperatures occur. In this layer, thecold temperatures cause the raindrops to freeze intoice pellets during their transit to the ground surface.Similar to freezing rain, an air temperature inversion isrequired for the formation of ice pellets.

Snow is a type of precipitation common to the midand high latitudes snow develops when water vapor depositsitself (skipping the liquid phase) directly on a six-sided(hexagon) deposition nuclei as a solid crystals, attemperatures below freezing. The unique form ofsnowflakes occurs because ice crystal growth is mostrapid at the six points associated with geometric shape


CONCEPTS OF GEOGRAPHYof the deposition nuclei. These points are more directlyexposed to the atmosphere and consequently convertmore water vapor into ice. Snow is usually generatedby frontal lifting associated with mid-latitude cyclones.Snowfall can occur in the fall, winter, and spring monthswhen atmospheric temperatures can drop belowfreezing. Much of the ground surface of North Americacan be covered with snow for several months during atypical year

Snow pellets or graupel are spherical white bits ofice that have a diameter less than 5 millimeters. Snow pelletsdevelop when super cooled droplets freeze onto the surfaceof falling snowflakes. Snow pellets usually fall for only abrief period of time when a precipitation event changesfrom ice pellets to snow.

Hail is a type of frozen precipitation that is morethan 5 millimeters in diameter. Hailstones often haveconcentric shells of ice alternating between those with awhite cloudy appearance and those that are clear. Thecloudy white shells contain partially melted snowflakes thatfreeze onto the surface of the growing hailstone. The clearshells develop when liquid water freezes to the hailstonesurface. Strong updrafts in mature thunderstorm cloudsprovide the mechanism for hail formation. These updraftsmove hailstone embryos (often large frozen raindrops)upward through the storm cloud where they encounterlayers of ice crystals, snow, and super cooled rain Eachencounter causes the hailstone to grow larger in size asice, snow, and rain accretes to the surface. Hailstones cangrow very large in size when they are carried upward bymore than one updraft. When the hailstone becomes tooheavy to be supported by updrafts, it begins falling underthe influence of gravity. Descending hailstones can lose asignificant amount of their mass because of melting asthey encounter the warm air found in between the cloudbase and the Earth’s surface. Small hailstones often meltcompletely before they reach the ground.Fog :

Fog is simply a cloud of minute water droplets thatexists at ground level. Fog develops when the air at groundlevel is cooled enough to cause saturation (relative humidityequals 100 %). Meteorologists have a very specificdefinition to determine if fog exists. This definitionsuggests that fog is occurring when the visibility of theatmosphere, near the Earth’s surface, becomes less than1 kilometer. Fog can be created by a variety ofprocesses:

Radiation fog or ground fog, is produced by nearsurface cooling of the atmosphere due to long waveradiation emission. This particular type of fog is normallyquite shallow and develops during the evening hours.Shortly after sunrise the radiation fog disappears becauseof surface heating due to the absorption of solar radiation.

Upslope fog is created when air flows over highertopography. When the air is forced to rise in altitudebecause of the topographic barrier, it is cooled by

adiabatic expansion. This type of fog is often foundforming on the windward slopes of hills or mountains.

Advection fog is generated when air flows over asurface with a different temperature. Warm air advectioncan produce fog if it flows over a cold surface. The contactcooling associated with this process causes saturation tooccur in a relatively thin layer of air immediately abovethe ground surface.

Evaporation fog is a specific type of advection fog.It occurs when you get cold air advancing over warm wateror warm, moist land surfaces. In this situation, fog formsas water from the surface evaporates into the cold air andthen saturates (Figure 8f-6). This type of fog can also becalled steam fog or sea smoke.

Frontal fog is a type of fog that is associated withweather fronts, particularly warm fronts. In this situation,rain descending into the colder air ahead of the warm frontcan increase the quantity of water vapor in this atmospherethrough evaporation. Fog then forms when the quantityof water in the atmosphere ahead of the front reachessaturation (relative humidity equals 100 %).Global Distribution of Precipitation

The Global Precipitation Climatology Project(GPCP) was established by the World Climate ResearchProgram (WCRP) in 1986 with the goal of providingmonthly mean precipitation data on a global scale.

The GPCP has accomplished this by combininginfrared and microwave satellite estimates of precipitationwith rain gauge data from more than 30,000 stations.

Infrared precipitation measurements are obtainedfrom GOES (United States), GMS (Japan) and Meteosat(European Community) geostationary satellites andNational Oceanic and Atmospheric Administration(NOAA) operational polar orbiting satellites. Microwaveestimates are obtained from the U.S. DefenseMeteorological Satellite Program (DMSP) satellites usingthe Special Sensor Microwave Imager (SSM/I).

Together these data sets will be used to validate generalcirculation and climate models, study the global hydrologicalcycle and diagnose the variability of the global climatesystem.

The average annual precipitation of the entiresurface of our planet is estimated to be about 1050millimeters per year or approximately 88 millimeters permonth.

However the actual values vary spatially from less than10 millimeters per month or to a maximum of more than300 millimeters per month depending on location. Thereasons for these patterns are as follows:

The deserts in the subtropical regions occur becausethese areas do not contain any mechanism for lifting airmasses. In fact, these areas are dominated by subsiding airthat results from global circulation patterns. Continentalareas tend to be dry because of their distance frommoisture sources.


CONCEPTS OF GEOGRAPHYPolar areas are dry because cold air cannot hold

as much moisture as warm air.Areas near the equator achieve high rainfall amounts

because constant solar heating encourages convection, andglobal circulation patterns cause northern and southern airmasses to converge here causing frontal lifting.

Mid-latitudes experience cyclonic activity andfrontal lifting when polar and subtropical air massesmeet at the polar front. Further, the air masses in thisregion generally move from West to East, causing levelsof precipitation to decrease East of source regions.

Mountain ranges near water sources can receivehigh rainfalls because of orographic uplift, if and onlyif the prevailing winds are in their favor. This can alsoresult in a sharp reduction in rainfall in regions adjacentor on the leeward slopes of these areas. Thisphenomenon is commonly known as the rain shadoweffect.Acid Precipitation

The term acid precipitation is used to specificallydescribe wet forms of acid pollution that can be found inrain, sleet, snow, fog, and cloud vapor.

An acid can be defined as any substance that whendissolved in water dissociates to yield corrosive hydrogenions. The acidity of substances dissolved in water iscommonly measured in terms of pH (defined as thenegative logarithm of the concentration of hydrogen ions).

According to this measurement scale solutions withpHs less than 7 are described as being acidic, while a pHgreater than 7.0 is considered alkaline.

Precipitation normally has a pH between 5.0 to 5.6because of natural atmospheric reactions involving carbondioxide.

For comparison, distilled water, pure of any otherstub stances, would have a pH of 7.0. Precipitation isconsidered to be acidic when its pH falls below 5.6 (whichis 25 times more acidic than pure distilled water).

In the 17th century, scientists noted the ill effects thatindustry and acidic pollution was having on vegetation andpeople. However, the term acid rain was first used twocenturies later when Angus Smith published a book called

‘Acid Rain’ in 1872. In the 1960s, the problems associated with acid

deposition became an international problem whenfishermen noticed declines in fish numbers and diversityin many lakes throughout North America and Europe.

Acid Rain FormationAcid Rain can form as a result of two processes.

In some cases, hydrochloric acid can be expelleddirectly into the atmosphere.

More commonly it is due to secondary pollutantsthat form from the oxidation of nitrogen oxides (NOx)or sulfur dioxide (SO2) gases that are released into theatmosphere.

Reactions at the Earth’s surface or within theatmosphere can convert these pollutants into nitric acidor sulfuric acid.

Acid precipitation formation can also take placeat the Earth’s surface when nitrogen oxides and sulfurdioxide settle on the landscape and interact with dewor frost.

Emissions of sulfur dioxide are responsible for 60-70 % of the acid deposition that occurs globally. Morethan 90 % of the sulfur in the atmosphere is of humanorigin. The main sources of sulfur include:

Coal burning - coal typically contains 2-3 % sulfurso when it is burned sulfur dioxide is liberated.

The smelting of metal sulfide ores to obtain thepure metals. Metals such as zinc, nickel, and copperare all commonly obtained in this manner.

Volcanic eruptions - although this is not awidespread problem, a volcanic eruption can add a lotof sulfur to the atmosphere in a regional area.

Ocean spray.After being released into the atmosphere, sulfur

dioxide can either be deposited on the Earth’s surfacein the form of dry deposition or it can undergo thefollowing reactions to produce acids that areincorporated into the products of wet deposition:

SO2 + H2O »»» H2SO3H2SO3 + 1/2O2 »»» H2SO4

Record Location Amount (mm) Date

1-year Rainfall Cherrapundi, India 26,470 1861

1-month Rainfall Cherrapundi, India 9300 1861 (July)

Average Annual Rainfall Mt. Waialeale, Hawaii, USA 11,680

24 hr. Rainfall Belouve, La Reunion Island 1350 Feb 28, 1964

Lowest Annual Average Rainfall

Arica, Chile 0.8

Greatest 1 Month Snowfall

Tamarack, California, USA 9910 1911 (Jan)

Greatest Snowfall Single Storm

Mt. Shasta, California, USA 4800 Feb 13-19, 1959

Precipitation extreme weather records.


CONCEPTS OF GEOGRAPHYSeveral processes can result in the formation of

acid deposition. Nitrogen oxides (NOx) and sulfur dioxide (SO2)

released into the atmosphere from a variety of sourcescall fall to the ground simply as dry deposition.

This dry deposition can then be converted intoacids when these deposited chemicals meet water.

Most wet acid deposition forms when nitrogenoxides (NOx) and sulfur dioxide (SO2) are converted tonitric acid (HNO3) and sulfuric acid (H2SO4) throughoxidation and dissolution. Wet deposition can also formwhen ammonia gas (NH3) from natural sources isconverted into ammonium (NH4).

Some 95 % of the elevated levels of nitrogen oxidesin the atmosphere are the result of human activities.The remaining 5 % comes from several naturalprocesses. The major sources of nitrogen oxides include:

Combustion of oil, coal, and gas.Bacterial action in soil.Forest fires.Volcanic action.Lightning.Acids of nitrogen form as a result of the following

atmospheric chemical reactions:NO + 1/2O2 »»» NO22NO2 + H2O »»» HNO2 + HNO3NO2 + OH »»» HNO3 The concentrations of both nitrogen oxides and

sulfur dioxides are much lower than atmospheric carbondioxide, which is mainly responsible for making naturalrainwater slightly acidic.

However, these gases are much more soluble thancarbon dioxide and therefore have a much greater effecton the pH of the precipitation. Effects of Acid Deposition

Acid deposition influences the environment inseveral different ways. In aquatic systems, aciddeposition can affect these ecosystems by lowering theirpH.

Streams, ponds, or lakes that exist on bedrock orsediments rich in calcium and/or magnesium arenaturally buffered from the effects of acid deposition.

Aquatic systems on neutral or acidic bedrock arenormally very sensitive to acid deposition because theylack basic compounds that buffer acidification.

In Canada, many of the water bodies found on thegranitic Canadian Shield fall in this group.

One of the most obvious effects of aquaticacidification is high concentration of toxic heavy metalslike mercury, aluminum, and cadmium in the waterbodies. The source of these heavy metals was the soiland bedrock surrounding the water body. Normally,

these chemicals are found locked in clay particles,minerals, and rocks. However, the acidification ofterrestrial soils and bedrock can cause these metals tobecome soluble. Once soluble, these toxic metals areeasily leached by infiltrating water into aquatic systemswhere they accumulate to toxic levels.

In the middle latitudes, many acidified aquaticsystems experience a phenomenon known as acid shock.During the winter the acidic deposits can buildup inthe snow pack. With the arrival of spring, snow packbegins to melt quickly and the acids are released overa short period of time at concentrations 5 to 10 timesmore acidic than rainfall. Most adult fish can survivethis shock. However, the eggs and small fry of muchspring spawning species are extremely sensitive to thisacidification.

The severity of the impact of acid deposition onvegetation is greatly dependent on the type of soil theplants grow in.

Similar to surface water acidification, many soilshave a natural buffering capacity and are able toneutralize acid inputs.

In general, soils that have a lot of lime are betterat neutralizing acids than those that are made up ofsiliceous sand or weathered acidic bedrock.

In less buffered soils, vegetation is effected by aciddeposition because:

Increasing acidity results in the leaching of severalimportant plant nutrients, including calcium, potassium,and magnesium. Reductions in the availability of thesenutrients cause a decline in plant growth rates.

The heavy metal aluminum becomes more mobilein acidified soils. Aluminum can damage roots andinterfere with plant uptake of other nutrients such asmagnesium and potassium.

Reductions in soil pH can cause germination ofseeds and the growth of young seedlings to be inhibited.

Many important soil organisms cannot survive issoils below a pH of about 6.0. The death of theseorganisms can inhibit decomposition and nutrientcycling.

High concentrations of nitric acid can increase theavailability of nitrogen and reduce the availability ofother nutrients necessary for plant growth. As a result,the plants become over-fertilized by nitrogen (acondition known as nitrogen saturation).

Acid precipitation can cause direct damage to thefoliage on plants especially when the precipitation is inthe form of fog or cloud water, which is up to tentimes more acidic than rainfall.

Dry deposition of SO2 and NOx has been foundto affect the ability of leaves to retain water when theyare under water stress.

Acidic deposition can leach nutrients from the plant


CONCEPTS OF GEOGRAPHYtissues weakening their structure. Weakening theirstructure.

The combination of these effects can lead to plantsthat have reduced growth rates, flowering ability andyields. It also makes plants more vulnerable to diseases,insects, droughts and frosts.

The effects of acidic deposition on humans can beas follows:

Toxic metals, such as mercury and aluminum, canbe released into the environment through theacidification of soils. The toxic metals can then end upin the drinking water, crops, and fish, and are theningested by humans through consumption. If ingestedin great quantities, these metals can have toxic effectson human health. One metal, aluminum, is believed tobe related to the occurrence of Alzheimer’s disease.

Increased concentrations of sulfur dioxide andoxides of nitrogen have been correlated to increasedhospital admissions for respiratory illness.

Research on children from communities that receive ahigh amount of acidic pollution show increasedfrequencies of chest colds, allergies, and coughs.Evaporation and Transpiration

Water is removed from the surface of the Earth tothe atmosphere by two distinct mechanisms: evaporationand transpiration.

Evaporation can be defined as the process whereliquid water is transformed into a gaseous state.

Evaporation can only occur when water is available.It also requires that the humidity of the atmosphere beless than the evaporating surface (at 100 % relativehumidity there is no more evaporation).

The evaporation process requires large amounts ofenergy. For example, the evaporation of one gram of waterrequires 600 calories of heat energy.

Transpiration is the process of water loss from plantsthrough stomata. Stomata are small openings found onthe underside of leaves that are connected to vascular planttissues.

In most plants, transpiration is a passive processlargely controlled by the humidity of the atmosphericand the moisture content of the soil.

Of the transpired water passing through a plant only1 % is used in the growth process. Transpiration alsotransports nutrients from the soil into the roots and carriesthem to the various cells of the plant and is used to keeptissues from becoming overheated.

Some dry environment plants do have the ability toopen and close their stomata. This adaptation is necessaryto limit the loss of water from plant tissues. Without thisadaptation these plants would not be able to survive underconditions of severe drought.

It is often difficult to distinguish between evaporation

and transpiration. So we use a composite termevapotranspiration. The rate of evapotranspiration at anyinstant from the Earth’s surface is controlled by fourfactors:

Energy availability: The more energy available thegreater the rate of evapotranspiration. It takes about 600calories of heat energy to change 1 gram of liquid waterinto a gas.

The humidity gradient away from the surface: Therate and quantity of water vapor entering into theatmosphere both become higher in drier air.

The wind speed immediately above the surface:Many of us have observed that our gardens need morewatering on windy days compared to calm days whentemperatures are similar. This fact occurs because windincreases the potential for evapotranspiration. The processof evapotranspiration moves water vapor from ground orwater surfaces to an adjacent shallow layer that is only afew centimeters thick. When this layer becomes saturatedevapotranspiration stops. However, wind can remove thislayer replacing it with drier air, which increases the potentialfor evapotranspiration.

Water availability: Evapotranspiration cannot occurif water is not available.

On a global scale, most of the evapotranspiration ofwater on the Earth’s surface occurs in the subtropicaloceans.

In these areas, high quantities of solar radiationprovide the energy required to convert liquid water into agas.

Evapotranspiration generally exceeds precipitation onmiddle and high latitude landmass areas during the summerseason.

Once again, the greater availability of solar radiationduring this time enhances the evapotranspiration process.

OceansSeen from space, the planet Earth appears blue

because large bodies of saline water known as the oceansdominate the surface.

Oceans cover approximately 70.8 % or 361 millionsquare kilometers (139 million square miles) of Earth’ssurface with a volume of about 1370 million cubickilometers (329 million cubic miles).

The average depth of these extensive bodies of seawater is about 3.8 kilometers (2.4 miles). Maximum depthscan exceed 10 kilometers (6.2 miles) in a number of areasknown as ocean trenches.

The oceans contain 97 % of our planet’s availablewater. The other 3 % is found in atmosphere, on theEarth’s terrestrial surface, or in the Earth’s lithosphere invarious forms and stores as Hydrologic CycleSurface Percent of Area Area

Earth’s Total Square SquareSurfacea Area Kilometers Miles


CONCEPTS OF GEOGRAPHYEarth’s Surface AreaCovered by Land 29.2% 148,940,000 57,491,000Earth’s Surface AreaCovered by Water 70.8% 361,132,000 139,397,000Pacific Ocean 30.5% 155,557,000 60,045,000Atlantic Ocean 20.8% 76,762,000 29,630,000Indian Ocean 14.4% 68,556,000 26,463,000Southern Ocean 4.0% 20,327,000 7,846,000Arctic Ocean 2.8% 14,056,000 5,426,000

Surface area of our planet covered by oceans andcontinents

The spatial distribution of ocean regions andcontinents is unevenly arranged across the Earth’s surface.In the Northern Hemisphere, the ratio of land to ocean isabout 1 to 1.5.

The ratio of land to ocean in the SouthernHemisphere is 1 to 4.

This greater abundance of ocean surface has somefascinating effects on the environment of the southern halfof our planet. For example, climate of SouthernHemisphere locations is often more moderate whencompared to similar places in the NorthernHemisphere. This fact is primarily due to the presenceof large amounts of heat energy stored in the oceans.

The International Hydrographic Organization hasdivided and named the interconnected oceans of the worldinto five main regions: Atlantic Ocean, Arctic Ocean,Indian Ocean, Pacific Ocean, and the Southern Oceanor Antarctica ocean. Each one of these regions is differentfrom the others in some specific ways.Atlantic Ocean

The Atlantic Ocean is a relatively narrow body ofwater that snakes between nearly parallel continentalmasses covering about 21 % of the Earth’s total surfacearea.

This ocean body contains most of our planet’s shallowseas, but it has relatively few islands. Some of the shallowseas found in the Atlantic Ocean include the Caribbean,Mediterranean, Baltic, Black, North, Baltic, and the Gulfof Mexico.

The average depth of the Atlantic Ocean (includingits adjacent seas) is about 3300 meters (10,800 feet).

The deepest point, 8605 meters (28,232 feet), occursin the Puerto Rico Trench.

The Mid-Atlantic Ridge, running roughly down thecenter of this ocean region, separates the Atlantic Oceaninto two large basins.

Many streams empty their fresh water dischargeinto the Atlantic Ocean. In fact, the Atlantic Oceanreceives more freshwater from terrestrial runoff thanany other ocean region.

This ocean region also drains some of the Earth’slargest rivers including the Amazon Mississippi, St.Lawrence, and Congo.

The surface area of the Atlantic Ocean is about1.6 times greater than the terrestrial area providingrunoff.

Arctic Ocean The Arctic Ocean is the smallest of the world’s five

ocean regions, covering about 3 % of the Earth’s totalsurface area.

Most of this nearly landlocked ocean region islocated north of the Arctic Circle.

The Arctic Ocean is connected to the Atlantic Oceanby the Greenland Sea, and the Pacific Ocean via the BeringStrait.

The Arctic Ocean is also the shallowest ocean regionwith an average depth of 1050 meters (3450 feet).

The center of the Arctic Ocean is covered by adrifting persistent icepack that has an average thicknessof about 3 meters (10 feet).

During the winter months, this sea ice covers muchof the Arctic Ocean surface.

Higher temperatures in the summer months causethe icepack to seasonally shrink in extent by about 50%.Indian Ocean

The Indian Ocean covers about 14 % of the Earth’ssurface area.

This ocean region is enclosed on three sides by thelandmasses of Africa, Asia, and Australia.

The Indian Ocean’s southern border is open to waterexchange with the much colder Southern Ocean.

Average depth of the Indian Ocean is 3900 meters(12,800 feet). The deepest point in this ocean region occursin the Java Trench with a depth of 7258 meters (23,812feet) below sea level.

The Indian Ocean region has relatively few islands.Continental shelf areas tend to be quite narrow and notmany shallow seas exist.

Relative to the Atlantic Ocean, only a small numberof streams drain into the Indian Ocean.

Consequently, the surface area of the Indian Ocean isapproximately 400 % larger than the land area supplyrunoff into it.

Some of the major rivers flowing into the IndianOcean include the Zambezi, Arvandrud/Shatt-al-Arab,Indus, Ganges, Brahmaputra, and the Irrawaddy.

Seawater salinity ranges between 32 and 37 partsper 1000.

Because much of the Indian Ocean lies within thetropics, this basin has the warmest surface oceantemperatures.

Pacific OceanThe Pacific Ocean is the largest ocean region,


CONCEPTS OF GEOGRAPHYcovering about 30 % of the Earth’s surface area (about15 times the size of the United States).

The ocean floor of the Pacific is quite uniform indepth having an average elevation of 4300 meters (14,100feet) below sea level.

This fact makes it the deepest ocean region onaverage. The Pacific Ocean is also home to the lowestelevation on our planet. The deepest point in theMariana Trench lies some 10,911 meters (35,840 feet)below sea level as recorded by the Japanese probe,Kaiko, on March 24, 1995.

About 25,000 islands can be found in the PacificOcean region. This is more than the number for the otherfour ocean regions combined.

Many of these islands are actually the tops ofvolcanic mountains created by the release of molten rockfrom beneath the ocean floor.

Relative to the Atlantic Ocean, only a smallnumber of rivers add terrestrial freshwater runoff tothe Pacific Ocean.

In fact, the surface area of the Pacific is about1000 % greater than the land area that drains into it.Some of the major rivers flowing into this ocean regioninclude the Colorado, Columbia, Fraser, Mekong, RíoGrande de Santiago, San Joaquin, Shinano, Skeena,Stikine, Xi Jiang, and Yukon.

Some of larger adjacent seas connected to thePacific are Celebes, Tasman, Coral, East China, Sulu,South China, Yellow, and the Sea of Japan.

Southern Ocean or Antarctica OceanThe Southern Ocean surrounds Antarctica

extending to the latitude 60° South.This ocean region occupies about 4 % of the Earth’s

surface or about 20,327,000 square kilometers (7,846,000square miles).

Relative to the other ocean regions, the floor ofthe Southern Ocean is quite deep ranging from 4000 to5000 meters (13,100 to 16,400 feet) below sea level overmost of the area it occupies.

Continental shelf areas are very limited and aremainly found around Antarctica. But even these areasare quite deep with an elevation between 400 to 800meters (1300 to 2600 feet) below sea level.

For comparison, the average depth of thecontinental shelf for the entire planet is about 130 meters(425 feet).

The Southern Ocean’s deepest point is in the SouthSandwich Trench at 7235 meters (23,3737 feet) sea level.Seas adjacent to this ocean region include the AmundsenSea, Bellingshausen Sea, Ross Sea, Scotia Sea, and theWeddell Sea.

By about September of each year, a mobileicepack situated around Antarctic reaches its greatestseasonal extent covering about 19 million square

kilometers (7 million square miles). This icepackshrinks by around 85 % six months later in March

Physical and Chemical Characteristics of SeawaterMost of the dissolved chemical constituents or salts

found in seawater have a continental origin. These chemicals were released from continental

rocks through weathering and then carried to the oceansby stream runoff.

Only six elements and compounds comprise about99 % of sea salts: chlorine (Cl-), sodium (Na+), sulfur(SO4

-2), magnesium (Mg+2), calcium (Ca+2), andpotassium (K+).

The relative abundance of the major salts inseawater are constant regardless of the ocean. Only theamount of water in the mixture varies because ofdifferences between ocean basins because of regionaldifferences in freshwater loss (evaporation) and gain(runoff and precipitation).

The chlorine ion makes up 55 % of the salt inseawater.

Calculations of seawater salinity are made of theparts per 1000 of the chlorine ion present in onekilogram of seawater.

Typically, seawater has a salinity of 35 parts perthousand.

Seawater freezes at a temperature that is slightlycolder than fresh water (0.0° Celsius).

The freezing temperature of seawater also varieswith the concentration of salts. More salt the lower theinitial freezing temperature.

At a salinity of 35 parts per thousand, seawaterfreezes at a temperature of -1.9° Celsius.

Seawater also contains small amounts of dissolvedgases. Many of these gases are added to seawater fromthe atmosphere through the constant stirring of the seasurface by wind and waves.

The concentration of gases that can be dissolvedinto seawater from the atmosphere is determined bytemperature and salinity of the water.

Increasing the temperature or salinity reduces theamount of gas that ocean water can dissolve.

Some of the important atmospheric gases foundin seawater include: nitrogen, oxygen, carbon dioxide(in the form of bicarbonate HCO3), argon, helium, andneon.

Compared to the other atmospheric gases, theamount of carbon dioxide dissolved in saturatedseawater is unusually large.

Some gases found within seawater are also involvedin oceanic organic and inorganic processes that areindirectly related to the atmosphere. For example,oxygen and carbon dioxide may be temporally generatedor depleted by such processes to varying concentrationsat specific locations within the ocean.

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