Points – 53 Lecture #9 Light Matter Today 1. Nature of Light 2. Properties of Matter Readings Chapter 5 (sections 1-3) How do we experience Light? - Warmth (sun) - Color Colors is Light - Light is made up of many different colors o Very hot material emits visible light (sun, wire in light bulb) o Cool light (from a chair) doesn’t emit visible light by itself Absorbs and reflects it i.e. Red Chair = absorbs blue light, reflects red light How do light and matter interact? - Emission - Absorption o Materials that absorb = opaque - Transmission (allow some to pass through) o Materials that transmit = transparent - Reflection (or redirecting or scattering) o Reflection = bouncing in same general direction o Scattering = more random Recap
Transcript
Points – 53
Lecture #9Light Matter
Today1. Nature of Light2. Properties of Matter
Readings Chapter 5 (sections 1-3)
How do we experience Light?- Warmth (sun)- Color
Colors is Light- Light is made up of many different colors
o Very hot material emits visible light (sun, wire in light bulb)o Cool light (from a chair) doesn’t emit visible light by itself
Absorbs and reflects it i.e. Red Chair = absorbs blue light, reflects red light
How do light and matter interact?- Emission - Absorption
o Materials that absorb = opaque- Transmission (allow some to pass through)
o Materials that transmit = transparent- Reflection (or redirecting or scattering)
o Reflection = bouncing in same general directiono Scattering = more random
Recap- How do we experience light?
o Light is a form of energyo Light comes in many colors that combine to form white light
- How does light interact with matter?o Matter can emit, absorb, transmit, and reflect (redirect/scatter) lighto Interactions between light and matter determine the appearance of everything we
see around us
Part 2 What is light?
- Light can act either like a wave or like a particle- Particles of light are called photons
Waves- Pebble in the pond analogy
o Waves ripple in the pond Consists of trough (water lower than average) and peaks (water higher
than average)o Leaf in pond will rise and fall with peaks and troughs but won’t move waves
carry energy outward but do not carry matter along with them- Particle = thing- Wave = pattern revealed by interactions with particles
Properties of Waves- 3 basic properties of waves: wavelength, frequency, and speed- Wavelength
o Distance from one peak to the next- Frequency
o Number of times (per sec) that a wave vibrates up and down “cycles per second” often called Hertz (Hz)
- Wave Speed o Wave Speed = Wavelength x Frequency
Tells us how fast their peaks travel
Light: Electromagnetic Waves- A light wave is a vibration of electric and magnetic fields
o Light is an electromagnetic wave Causes electrons to bob up and down – wriggle as a snake as light passed
byo A field is used to describe the force an object would feel when in a certain space
- Light interacts with charged particles through these electric and magnetic fieldso Light always travels at the speed of light (about 300,000 km per sec)
Wavelength x Frequency = Speed of Light (c)o So there is an inverse relationship between Frequency and Wavelength
Longer Wavelength = Shorter Frequency Examples
If W is 1cm, F must be 30 GHz Therefore, if W = .5cm F would double to 60 GHz W = .25cm F = 120 GHz
Particles of Light- Particles of Light are called photons
o Has properties of both particles and waves- Each photon has a wavelength and a frequency- The energy of a photon depends of its frequency
o Directly proportional to its frequencyo E = h x f
H is called “Planck’s Constant”
Electromagnetic Spectrum- Light we can see = Visible Light
o 400nm – 700nm (Blue Red)- In order of Short Long Wavelengths
o Gamma rays, X-Rays, UV rays, Visible, Infrared, Radioo High frequency low frequency (inversely proportional to wavelength)o Large energy per photon small energy per photon
- Infrared Light o Wavelengths somewhat longer than red lights
Lies beyond red in the spectrum I.E. Jupiter
- Radio Waveso We hear sound waves from the car radio, not electromagnetic waveso Sometimes given the name microwaves
Radar, Microwave ovens Cosmic microwave background Radio images of Galaxies (Centaurus
A)- Ultraviolet (UV) Light
o Just to the left of visible light (violet) Example: The Sun
o Mostly absorbed by the ozone in the atmosphere o Can cause skin cancer
- X-Rayso Very short, very energetic wavelengths (left of UV, right of Gamma)o Can penetrate through tissues, but not bones
- Gamma Rayso Most energetic, shortest wavelengthso Extremely Violent events
Recap: Properties of Light- What is light?
o Can behave either like a wave or a particleo A light wave is a vibration of electric and magnetic fieldso Light waves have a wavelength and a frequencyo Photons are particle of light
- What is the electromagnetic spectrum?o Human eyes cannot see most forms of lighto The entire range of wavelengths of light is known as the electromagnetic
spectrum
Properties of MatterWhat to know
- What is the structure of matter?- What are the phases of matter?
What is the Structure of Matter- Electron (Negative), Protons (Positive – Red), and Neutrons (Neutral – Grey)- Atomic Terms
o Atomic Number – number of protons in nucleus Number of electrons = number of protons
o Atomic Mass – number of protons and neutronso Molecules – consist of two or more atomso Isotopes – Atoms with same number of protons, but different number of neutrons
Phases of Matter- Solid, liquid, gas
o Phases depend primarily on temperature but are also affected by pressure
Temperature- Measures how fast particles (atoms or molecules) move
Temp. Scales- Water Boils around 100 C- Freezes at 0 C- Absolute Zero = -273.15 C- Room Temp = 0 C or 300K
Phase Changes- Melting: Breaking of rigid lattice; solid liquid- Evaporation : Breaking of chemical bonds; liquid gas- Dissociation : Breaking of molecules into atoms
- Ionization: Stripping of electrons, changing atoms into plasma o Free elections and ions
- Often more than one phase is present
Lecture #10Matter and Shit
Today1. Matter (Cont., recap)2. Inferring properties of matter from light3. Inferring motions of objects from light
Readings Chapter 5 (sections 4 and 5)
Energy Levels in Atoms- Electrons in an atom are held in orbit around nucleus by electrical force
o Kind of like a planet around a sun- Can occupy many discrete orbits
o Each orbit is an energy level (like the rungs on a latter specific heights)
Recap- What is the structure of matter
o Matter is made of atoms, which consist of a nucleus of protons and neutrons surrounded by a cloud of electrons
- What are the phases of mattero As temperature rises, a substance transforms from a solid to a liquid to a gas, then
the molecules can dissociate into atoms (more than one can co-exist, thought)o Stripping of electrons from atoms (ionization) turns the substance into a plasms
- How is energy stored in atoms?o The energies of electrons in atoms correspond to discrete energy levels
Learning From Light- What to know
o What are the three basic types of spectra?o How does light tell us what things are made of?o How does light tell us the temperature of light emitters?
- Spectra o Most astronomical information comes from spectra of light
Spectrum = distribution of light intensity at different wavelengthso A graph of intensity vs. wavelength
Three Types of Spectra- Continuous Spectrum (Light Bulb)
o Kirchhoff’s First Law – Spans all visible wavelengths without interruption- Emission Spectrum (Neon Lamp)
o Thin/low-density cloud of hot gas emits light only at specific wavelengths producing a spectrum with bright emission lines
Kirchhoff’s Second Law- Absorption line Spectrum
o Cloud of cool gas between us and a light bulb can absorb light of specific wavelengths, leaving dark absorption lines in the spectrum
o Kirchhoff’s Third Law
Recap: 3 Types of Spectra- Continuous
o Hot and Dense- Emission
o Hot and Diffuse cloud of gaso Mostly Black, light emitted only at specific colors
- Absorptiono Hot and Dense light source then cool and diffuse gaso Mostly colors, light absorbed at specific colors
Inferring Properties of Matter from LightWhy do we see emission spectrum?
- Thermal motions lead to collisionso Collisions lead to excitation of atoms to higher energy levelso De-excitation of atoms leads to emission of photons
Photon energy = energy difference between levels
Chemical Fingerprints- Each type of atom has a unique set of energy levels or a spectral fingerprint
o Each transition corresponds to a unique photon energy (color) Downward transitions produce a unique pattern of emission lines (colors)
Energy Levels of Molecules- Molecules have additional energy levels because they can vibrate and rotate
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October 1 Lecture
TopicsDoppler Effect (Cont.)TelescopesOverview of Planets
TelescopesWhat are the two basic types?
- Refracting Telescopeo Focuses light with lenses
Bending of light when passing from one medium (air) into another (glass) is called refraction
o Examples Galileo Refracting Telescope (1609) McCormick Observatory (UVA, 1883)
26 inch Refractor - Reflecting Telescope
oWhy bigger the better?
What do astronomers do with telescopes?- Imaging: Taking pictures of sky
o Astronomical detectors generally record only one color at a timeo Several imagines must be combined to make full-color pictures
- Spectroscopy: Sorting light into Spectra- Timing: ___________
Atmospheric EffectsHow does Earth’s atmosphere affect ground-based observations?
Why do we put telescopes into space?- Twinkling and Turbulence
o Turbulent air flow in Earth’s atmosphere distorts our view, causing stars to appear to twinkle
- Hubble Space Telescopeo Launched by Space Shuttle in 1990
Designed to be serviced regularly by space shuttleso Didn’t finish
LectureOctober 8
Points - 2
Last TimeTelescopes (Chapter 6)Overview of Solar System (7.1)
TodayOverview of Solar System cont. (7.1)Patterns in Solar System
What to know- What does the Solar System look like?- What are the major features of the Sun and planets?
Misleading Points- Orbital Shape
o All planets orbit in same directiono 8 major planets with DIDN’T FINISH
- Planetary Scaleo Planets much smaller than sun
- Size vs. Separationo ***Planets are tiny compared to the distances between them
Grapefruit Analogy (Shrink by factor of 10) Sun = grapefruit (14cm) Earth – 100x smaller, size of ballpoint pen (1.3 mm or .13cm) Jupiter = size of grape Sun – Earth Distance = 15 meters Sun – Jupiter Distances = About 75 meters
Planet sizes much much smaller than separations
Major Features of Objects in Solar System1. Size2. Distance3. Mass4. Composition5. Other Notable Features
Earth
- Radiuso 6,400 km = 1 R(subscript) Earth
- Diametero 13,000km
- Distance to Suno 150,000,000km = 1 AU (10,000x Dia. Of Earth)
- Average Densityo 5.5 g/cm3 (heavier than water)
- Compositiono Rocks and Metals
- Surface Temp. o 290 K or about 300K (liquid water)
- Important Featureso Only place known to have life at present timeo Only place with surface liquid and Oxygen in atmosphere in the solar system
Large amount of oxygen comparatively – deteriorates quickly but life replenishes it
o Surprisingly large moon (relative to size) Moon’s Radius is ¼ Earth’s Separation is about 30x the Diameter of the Earth = 1 Light Second Moon regulates the speed of the Earth through tidal friction
The Sun- Most dominating object in solar system- Biggest and most massive object- Size
o Radius 100 times R of Earth
o Mass 300x Earth’s (Less weight/density) 99.9% of solar system’s mass
o Volume 1003 of Earth
- Compositiono Mostly made of Hydrogen and Helium gas (98% by mass, 2% by others)
Why gas? – Very high surface temperature – 6,000K Not hot enough at surface for plasma
o Plasma found in area just outside the sun and inside the sun, just not at surface
- Thermal Radiation (Wien’s law, hotter, bluer)
o Wavelength of peak intensity = 3,000,000nm/ Temp. (K), for Sun, peaks at 500nm, in the visible (400-700nm)
Higher temperature = shorter wavelengthso Supply virtually all visible light in solar system (e.g. moon)o Why so hot at surface?
Strongly squeezed at center, temperature about 15 million K (plasma) Nuclear Reactions at the Center of the Sun
Converting about 4 million tons of matter into energy according to E = Mc2 per second
Middle Aged Used half of its Hydrogen Helium; About 5 billion years to go Clues to resolving the energy crisis on Earth?
Mass and Gravity allow for this temperature? Heat Hydrogen hot enough you can make Helium
Mercury- Density and Composition is similar to Earth (rocks and Metals)- Closest planet to the Sun
o .4 AU- Size
o Smaller than Eartho .4x Earth’s Radius
- Masso 20x less massive than Earth
- Densityo Similar to Eartho Volume is much smaller
- Compositiono Rocks and Metals (Similar to Earth)
- Notable Featureso Desolate, crated; little air; long, steep cliffso Very hot and very cold:
o Flyby by Mariner 10 (1974 – 1975) Least studied inner planet
o Messenger Spacecraft orbiting since 2011 (Launched 2004)
Venus- 2nd closest to the Sun
o .7 AU- Size, mass, and density similar to Earth – Earth’s Twin?
o Size = 0.95 Earth’s Radiuso Mass = 0.8 Earth’s (only 20% difference)o Made of Rocks and Metals
- Mysterious “evil” twin of Eartho Surface hidden by clouds
- Temperatureo 740Ko Even hotter than Mercury
470 Celsius day and nighto Hellish conditions due to an extreme greenhouse effect
Mostly Carbon Dioxide
Mars- Father away from Sun, 1.5 AU
o Almost twice as far as Venus- Size
o About 0.50 size as Earth 2x size of moon but slightly bigger than Mercury
- Masso About 10% of Earth’s
- Compositiono Rocks and Metals, like Earth
- Temperatureo About 220K (or -50 Celsius)
Colder than Earth- Moons
o Two tiny moons- Looks almost Earth-like, but very thin air
o Atmosphere isn’t made of Oxygen, very little Oxygen- Features
o Giant volcanoes, a huge canyon (stretches almost half of planet), polar caps of CO2
o Water flowed in distant past Could there have been life?
- Best studied Planet (besides Earth)o Chance of life surviving there
Jupiter- Distance
o 5AU, 12 years awayo Much farther from Sun
- Sizeo 11x Earth’s Radiuso Largest planet in solar system
- Masso 300x Earth
- Densityo 1.3 g/cm3
Lower than Earth (5.5)- Composition
o Mostly Hydrogen and Helium gas No solid surface
- Temperatureo 125 Ko Much colder than Earth and Inner planets
- Moonso More than 60 moonso And some (faint) rings
Saturn- Temperature
o Cloud top temp = 95K Colder than Jupiter
- Compositiono Giant and gaseous, mostly H and He
Just like Jupiter - Features
o Spectacular Ringso Many moons
Titan Second largest moon Lakes of Methane
Uranus- Discovered on March 13, 1781 by William Hershel
o Initially names George- Distance
o 20 AU Nearly twice as far from Sun as Saturm
o 84 year orbit Since discovery its orbited around like 3 times
- Size
o 4x Earth Smaller than Jupiter and Saturn
- Masso About 15x Earth
- Compositiono H and He gas and Hydrogen Compounds
Water, Ammonia (NH3) and Methane (CH4) Sets it apart
- Temperatureo Cloud-top = 60K (about 20% of Earths)
- Featureso Can’t see with Naked Eye (Unlike Jupiter and Saturn)o Many moons and ringso Extreme Axis Tilt
Most unique characteristic 42 year long daylight
Neptune- Distance
o 30AU (50% farther than Uranus)- Similar size, mass, composition, and temperature to Uranus- Has normal axis tilt- Features
o Many moons and rings Triton
Orbits the planet “backwards” (clock-wise) – different from all other big moons
Pluto- Discovered in 1930- Distance
o 40 AU at average Farther away from Neptune most of the time
Weird orbit, sometimes inside Neptune’s obrbit- Size
o .18x Earth Smaller than our moon
- Mass o .002x Earth (.2% or 500x less)
- Temperatureo 40K
- Compositiono Made of ice (like comets)
- Featureso Demoted to “Dwarf” planet in 2006 by IAU (International Astronomical Union)
Lecture October 22
Last TimeFormation of stars and disksFormation of planets (started)
TodayFormation of Planets (Cont.)Aftermath of planet formationAge of solar system Planet Geology (Chap. 9, if time)
ReadingChapter 8 (Sections 4 and 5) and Chapter 9
ReviewThe Great Divide
- Frost (or snow) line at 3.5 AU, where Temp. = 150Ko Inside frost line: Too hot for H compounds to form ices
Small solid particles of rock and metal onlyo Outside frost line: Cold enough for ices to form
Solid particles of ice as well as rock and metal
Step #1- Condensed solid particles are “seeds” of planet formation
Step #2- Collision and sticking of small solid particles together to form boulder-sized
planetesimals (pieces of planet, or building blocks of planet; about a KM)o Some are rocky (inside frost line) rocky planetso Some are icy (outside frost line) icy planets???
Step #3- Planetesimals merge together via gravitational attraction into a few planets called
“accretion”o As object grows the gravity increases – drawing more objects to the objects
But objects could smash into it, making it start over
How Did Terrestrial Planets Form?- Small particles of rock and metal condense inside frost line- Planetesimals of rock and metal build up > particles collided and stuck
- Mutual gravitational attraction eventually assembled these planetesimals into terrestrial planets
- Early Solar system was a very dangerous placeo Gravity pulling in all loose planetesimals and smashing into each other
How did Jovian planets form?Steps
1. Small particles of ice and rock/metal outside the frost line2. Larger (because ice is added – more to work with) planetesimals were able to form
through sticking3. Planetesimals merge via gravity into more massive icy/rocky protoplanetary cores of
about 10x mass of the Earth4. Gravity of these protoplanetary cores are able to draw in surrounding H and He gases bu
up to 300x Mass of Earth (Jupiter)a. One step further than the terrestrial planetsb. Key step
5. Miniature disks form around forming giant planets due to angular momentum conservation
a. Moons of Jovian planets form in miniature discs (disks within discs)b. Small fraction of mass of planet gets stuck orbiting the planet
What happened to the H and He gas in the terrestrial planet formation zone?Solar Wind
- Out-flowing matter from the Sun >> blew away the leftover gases not used to make the planets
o Winds are much stronger when stars are forming
What have we learned?- Why are there two types of planets?
o Because of temperature inside and outside of frost line- How did the terrestrial planets form?
o Rock and metals > small particleso Rocky/metal particles > planetesimalso Planetismals accreted >> planets
- How did Jovian planets formo Rock/Metal + ice > planets more massiveo Gravity of these massive planets draws in H, He Gaseso DIDN’T GET TO FINISH
- What happened to H and He Gases in Terrestrial planets?o Gone with the Wind (Solar Wind)
In-Class Exercise #1How would the solar system be different if the solar nebula had cooled, with a temperature half its actual value
- Jovian planets would have formed closer to Suno Frost line would be twice as close (3.5 AU 1.75 AU)
Review: Basic Patterns to be Explained1. Patterns of motion of the large bodies
Orbit in same direction and plane2. Existence of two types of planets
Terrestrial and Jovian3. Existence of smaller bodies
Asteroids and comets4. Notable exceptions to usual patterns
Rotation of Uranus, Earth’s moon, etc.
The Aftermath of Planet FormationWhere did asteroids and comets come from?
- Asteroids: rocky planetismals left over from terrestrial planet formation inside frost line o Between Mars and Jupiter
- Comets: icy planetesimals left over from jovian planet formation, outside the frost lineo Outside Neptune
Why “Exceptions to the Rules?”- Almost the same as answer to the asteroids (left over material not directly used to form
planets)o Only difference: not on stable orbit
Cross the orbit of other object – can crash into other things- Loose planetesimals bombarded other objects in the late stages of solar system formation
– era of “heavy bombardment” o Evidence seen in craterso Have loose planetesimals for the first .5 billion years or so
Exceptions Cont. -- Evidence of Heavy BombardmentOrigins of Earth’s water from heavy bombardment
- Earth was assembled from rocky planetesimals- Water may have come to Earth by way of icy planetesimals
o Delivered during period of heavy bombardment by loose icy planetesimals
Craters on planets
Mars should not have moons- Unusual moons of some planets may be captures planetesimals
How about our Moon?- Exceptional for terrestrial planets- Dozen or so planets formed initially in our Solar system – not all survived- Perhaps Moon created through a giant impact on the Earth by a Mars-sized “failed”
planet on loose orbito The collision stripped matter from Earth’s crust…then accreted into Moon….tilt
too?
What about odd spin axis of Uranus- Giant impacts might also explain the unusual spin axes of some planets
Recap- Where did asteroids and comets come from?
o Leftover planetesimals on stable orbits o DIDN’T GET TO FINISH
Summary: Origin of Solar System- A gas cloud collapses under its own weight into a star- A fraction of gas forms a rotating disk due to angular momentum conservation- Rocky particles inside frost line both rocky and icy outside- Particles stick together into planetesimals- Rocky terrestrial planets; icy Jovian- Jovian planetary cores capture H and He more massive
o Mini dicks around Jovian planets- Left-over planetesimals in stable orbits comets and asteroids
o Unstable heavy bombardment- Leftover gas blown away from terrestrial planets
In-Class Exercise #2Which of these facts about the solar system in NOT explained by the nebulary theory?
- Number of planets of each type (4 terrestrial and 4 Jovian)o Randomization to the creation
- Does explain…o There are two main types of planets: terrestrial and Joviano Planets orbit in same direction and in nearly the same planeo Existence of asteroids and comets
How to Determine Age of Solar SystemKey: Radioactive Isotopes
- Potassium used to date universeo 19 protons in nucleus
How to Determine Age of Solar System?- Atoms of radioactive 40K (19 protons and 21 neutrons) change spontaneously (or decay)
into atoms of Argon40 over time- The time for HALF of 40K atoms to become 40Argon is 1.25 Billion years- Argon is an inert gas that does NOT condense into solids
o If 40Ar is found in rocks it must be from radioactive 40Ko Amount of 40Ar relative it 40K depends on age of rock
Recap- How does radioactivity reveal an objects’ age?
o Some isotopes decay with a well-known half-life (K-40 and Ur-238)o Didn’t get to finish
Geology of Terrestrial WorldsSurface Features of Terrestrial Worlds
- Moon (.25 Earth) and Mercury (.4 Earth) have tons of crater- Earth – was originally covered with a ton of craters but they’ve been erase- Mars (.5 Earth)
o A lot more craters than Earth, but much less than surface of the moono Some geological activities erasing these craters
Geology not as active- Venus (.95 Earth)
o Covered mainly by clouds – harder to seeo Are things that drive volcanic activity
LectureOctober 29, 2015
Last TimeGeology of Moon, Mercury, and Mars
TodayGeology of Mars (Cont.)Geology of VenusAtmospheres of Planets
ReadingChapter 9 (Sections 9.4 and 9.5)Chapter 10 (Section 10.1)
Mars- Most explored planet- Watched long ass video clip about how hard it is to land things on Mars
Endurance Crater- Discovery by Mars Rover, Opportunity
o Lots of small spheres dubbed “blueberries” Can only be formed in standing water Strongest evidence yet of past abundant water
Cannot have water now – atmosphere too thin and it’s too cold
Phoenix Space Craft- Landed in polar region- Mission is to look for ice caps, frozen ice (not liquid ice)
o Water frost at 6am Fades immediately after sunrise
- Dug into Mars’ surface with small excavator o Sub-surface water ice – took about 4 days to evaporate
Could not be CO2 ice (evaporates in one day)
Recap- How Martians invaded popular culture
o Surface features of Mars misinterpreted as “canals”- What are major geological features of Mars?
o Differences in cratering across surfaceo Giant shield (extinct) volcanoeso Evidence of (past) tectonic activity
- Geological evidence for past water on Mars?o Features that look like dry riverbedso Rovers have found rocks (“blueberries”) that must be formed by watero Features on crater walls may indicate recent water flowso Subsurface water ice found by Phoenix spacecraft
VenusFacts
- Distance = .7AU- .95 Size of Earth- .80 Earth’s Mass- Orbital Period = 225 = 1 Venus year- Spin Period = 243 = 1 Venus day
o Slow and wrong directiono Slower that orbit around the sun
- Covered by thick clouds
Magellan Spacecraft- Launched May 4, 1989- Uses Radio waves from a Radar dish- Operated from 1990 – 1994- Mapped the entire surface
Cratering on Venus- Some impact craters, but far fewer than Moon, Mercury, and Mars- Relatively young surface of 750 million years- Relatively few small craters, uniformly spread out
Volcanoes on Venus- Many volcanoes, including both shield volcanoes and stratovolcanoes
o Many volcanoes in some regions- Some probably still active, because SO2 (sulfur dioxide) in atmosphere, from outgassing
from active volcanoes
Tectonics on Venus- Earth’s
o Keeps the surface of the Earth young features erased from surface as plates dive under each other
- Rugged terrains indicative of stresses (magma) below the surface- No plate tectonics on Venus
o Venus does not appear to have plate tectonics, but entire surface seems to have been “repaved” 750 million years ago for reasons not known
Little Erosion on Venus- Photos of rocks taken by a Russian Lander show little erosion
o No liquid water [rain] – too hot o Little surface wind – too slow spin
Atmospheric BasicsWhat is an atmosphere?
- All terrestrial worlds surrounded by a layer of gaso Huge difference in the gas, some extremely thin, others thick
- This layer of gas is called “atmosphere”
Earth’s Atmosphere- About 10km thick (Earth’s Radius = 6,400km)- Consists mostly of molecular nitrogen (N2) and oxygen (O2)
o Small amounts of other gas (i.e. CO2, H2O)
Atmospheric Pressure- Gas pressure depends on both density and temperature
o Adding air molecules increases the pressure in a balloono Heating the air also increases the pressure
- Pressure and density increase with altitude because the weight of overlying layers is less- Pressure at sea level
o 15 lbs. per square incho 1 bar
Where does an atmosphere end?- There is no clear upper boundary- Altitudes >60km are considered “space”
o Aurora extending up to 100km
Effects of Atmosphere- Create pressure that determines whether liquid water can - Didn’t finish
How is the temperature of a planet determined without greenhouse effect- The surface of a planet is heated mostly by sunlight (visible light can reach surface)- A fraction reflected back to space, remaining absorbed and turned into heat- Surface cooling by thermal radiation (infrared for typical T)
- Temperature determined by balance of Sunlight heating and loss of Infrared (IR) radiation into space
How does the greenhouse effect warm a planet?- Greenhouse gases in atmosphere (CO2, H20 vapor and methane CH4) absorb and reemit
IR photons, heating the lower atmospheres- Greenhouse gases act like a “blanket” to slow down heat leakage and keep a planet warm
