ASTRONOMY

It was in prehistoric times when humans first noted stars in the night sky, and it is where you can probably trace the roots of astronomy.

In modern times Astronomy is defined as the science of the universe outside of our planet. It is also the branch of physical science dealing with heavenly bodies.

BRANCHES OF ASTRONOMY1. Cosmology: Cosmologists study the Universe

as a whole, including its beginnings.2. Astrometry: Astrometrists measure great

distances.3. Planetology: Planetologists study planets

within our own Solar System as well as those orbiting distant stars.

4. Radio Astronomy: Radio Astronomers use radio-telescopes to study the Universe.

5. Mathematical Astronomy: Mathematical Astronomers who use numbers, calculations and statistics to explain the universe.

THE ASTRONOMICAL INSTRUMENTS1. Optical Telescopes: Possess a much larger

aperture than the human eye. This means that this can be used to collect much more of the light coming from distant object, which greatly improves resolution and clarity.

The Refracting TelescopeThis was the earliest design and in usually formed using two lens. The distance between two lenses, which are commonly placed near either end of a tube, can be adjusted to vary the resolution and magnification required. Any light passing through the forward lenses is refracted (bent) before being focused on the eyepiece lens.

2. A Radio Telescope: produces image with aid of a large concave mirror. The reflecting is also referred to as the Newtonian, after the English Astronomer Isaac Newton who first used this design to build a telescope around 1670.

3. Spectroscope: a narrow slit that is illuminated by the light source under study;

A collimator or tube and lens that produce a beam of parallel light rays; either glass or prism or a diffraction grating separate white light into its components and a telescope for viewing a spectrum.

4. Spectrograph: an instrument designed to photograph the spectrum instead of presenting it.

5. Photometer: An instrument for measuring the intensity of light. One of the light sources will be the star whose brightness is to be determined, the other will be star of known magnitude or an artificial star of known magnitude.

6. Interferometer: an instrument used to measure the angular diameter of the stars.

7. Thermocouple: is an extremely sensitive instrument used to measure the heat radiated from a celestial body.

8. Comparators: comparator or a blink microscope, is used for the examination of photographic plates taken of the same region of the sky at different times.

9. Chronograph: is an excellent means of recording astronomical observations accurately and permanently.

10. Coronagraph: was invented by Bernard Lyot around 1930. this device enables the corona of the sun to be studied at anytime without waiting for the occurrence of a solar eclipse.

THE UNIVERSE

Thales and Anaximander were the first ancient Greeks who first recorded scientific theory on the nature of the universe. Ptolemy described a finite universe ruled by the mathematicians and God in which the sun, planets, and other stars were attached to concentric spheres centered on the Earth.

HELIOCENTRIC UNIVERSEIt was Nicolaus Copernicus who revived the Greek idea that the Sun, and not the Earth, is the center of the universe.

THEORIES ON THE ORIGIN OF THE UNIVERSE

1. The Big Bang Theory This theory explains that the universe sprang

into existence as “singularity” around 13.7 billion years ago. This force can actually squished anything that goes on its way even light itself.

2. The Oscillating Theory The theory was credited to Richard Tolman who

saw it as a possible outcome of the Big Bang theory.

The theory emphasizes that the universe after expanding for years will soon grow cold and dark and die an ultimate heat death.

3. The Steady State Theory Austrian-British astronomer Hermann Bondi

and the Austrian-American astronomer Thomas Gold formulated the theory in 1948.

The British Astronomer Fred Hoyle soon published a different version of the theory based on his mathematical understanding of the problem.

The big bang theory and the steady state theory were both based on Bondi’s “cosmological principle”.it states that the universe is on a large scale, that it looks the same at every point.

GALAXIESA galaxy is essential an immense collection of stars which are held together by gravity. They range on size to shape.

TYPES OF GALAXIES

Elliptical Galaxies Galaxies of this class have smoothly varying

brightness, with the degree of brightness steadily decreasing outward from the center.

They appear elliptical in shape, with lines of equal brightness which is made up of concentric and similar ellipses.

These galaxies are nearly the entire same color, they are somewhat redder than the Sun.

ELLIPTICAL GALAXIES

Spiral Galaxies These galaxies are conspicuous for their spiral-

shaped arms, which emanate from or near the nucleus and gradually wind outward to the edge.

The nucleus of a spiral galaxy is sharp-peaked area of smooth texture, which can be quite small or, in some cases can make up the bulk of the galaxy

SPIRAL GALAXIES

Irregular Galaxies Consists of grainy, highly irregular assemblages

of luminous areas. They have no noticeable symmetry nor obvious

central nucleus, and they are generally bluer in colour than are the arms and disks of spiral galaxies

An extremely small number of them, however, are red have a smooth, though nonsymmetrical, shape.

IRREGULAR GALAXIES

The Milky Way Galaxy

Is a spiral system consisting of several billion stars, one of which is the Sun.

It takes its name from the Milky Way, the irregular luminous band of stars and gas clouds that stretches across the sky.

MILKY WAY GALAXY

STARSStars is a huge burning sphere of hot gas. The Sun is the nearest to Earth and the most comprehensively studied. The sun is just an ordinary star with ordinary size and brightness. Since the sun itself is a star, it can be used as reference for understanding all other the stars.

BRIGHTNESS OF STARS

A star has its own brightness but does not have the same brightness. The difference of brightness in stars can be related to

1. The amount of light produced by stars2. The size of each stars3. The distance to a particular star.

CLASSIFICATION OF BRIGHTNESS OF STARS

1. Apparent Magnitude – refers to how bright stars appear on Earth, taking relation the effect of the Earth’s atmosphere.

2. Absolute Magnitude – are expression of luminosity, or the total amount of energy radiated into space each second from the surface of the stars.

APPARENT MAGNITUDE

ABSOLUTE MAGNITUDE

COLOR AND TEMPERATURE

Stars have varying colors and temperature, and these are the bases of the different natures of stars. However, since the stars are too distant thus we can only identify their relative brightness, the brighter they appear the larger the image.

The color is a function of a star to determine its relative temperature.

Type Color Temperature (K)

Comment

O Bluish 30,000 – 80,000

Spectrum with Ionized helium and Hydrogen but little else; short-lived and rare stars

B Bluish 10,000 – 30,000

Spectrum with neutral helium, none ionized

A Bluish 7,500 – 10,000

Spectrum with no helium; strongest hydrogen, some magnesium and calcium

F White 6,000 – 7,500

Spectrum with Ionized calcium, magnesium, neutral atoms of iron

G Yellow 5,000 – 6,000

The spectral type of the sun, with 67 elements

K Orange – Red

3,500 – 5,000

Spectrum packed with lines from neutral metals

M Reddish 2,000 – 3,500

Band spectrum of molecules

THE LIFE CYCLE OF THE STARS

The Life of A Star A star is born in a gigantic cloud of gas

and dust in interstellar space, and then spends billion of years calmly shining while it fuses hydrogen nuclei in core.

According to Bill W. Tillery, the life cycle of stars are just theoretical framework based on the outcome of studies regarding nuclear reactions, which include nuclear fusion and fission.

PROTOSTAR STAGE The first stage of theoretical model of

stars. As gravity pulls the gas of a protostar

together, the density, pressure and temperature increase from the surface down to the center.

The mass of the star can start a simple nuclear fusion in the core.

The initial fusion combines four atoms of hydrogen to form helium thus releasing huge amount of energy.

RED GIANT STAGE Lesser hydrogen fusion reaction occurs, thus

less energy is released so the star begins to collapse.

The collapse heats the core, which now composed primarily of helium and the surrounding shell still have hydrogen.

The increase temperature causes hydrogen in the shell to undergo fusion, and the increased release of energy causes the outer layers of the stars to expand.

With an increased surface area, and the amount of radiation emitted per unit area is less, the star acquires a property of red giant.

BEGINNING OF THE END FOR LESS MASSIVE STAR

Less massive star may cool enough that the nuclei at the surface become neutral atoms rather than plasma.

The outer layer of stars begin to pulsate in and out, and a violent expansion blows off the outer layers of the stars, leaving the hot core.

The nebulae will continue to move away from the core of the star, leaving a carbon core and helium fusing shell begin to contract in a small, dense white dwarf star.

BEGINNING OF THE END OF MASSIVE STAR

A more massive star will definitely have different theoretical ending. It will also contract just like less massive star.

The heat from the star will used up all its energy, and will no longer maintain its internal temperature.

The star loses outward pressure of expansion from the high temperature thus, the star will collapse, then rebounds like a compressed spring into catastrophic explosion called a supermova.

TYPES OF STARSMain Sequence StarsRed GiantsWhite DwarfsBrown DwarfsVariable StarsBinary Stars

MAIN SEQUENCE

STARS

- is the point in a star’s evolution during which it maintains a stable nuclear reaction.Our Sun is a main sequence star.

RED GIANTS

– is a large star that is reddish or orange in color. It represents the late phase of development in a star’s life.The outer surface of the star expands and cools, giving it a reddish color.

WHITE DWARFS

Is the remnant of an average-sized stars that has passed through the red giant stage of its life after the star has used up its remaining fuel.

The star may expel some of its matter into space, creating a planetary nebula.

BROWN DWARFS

Also called as failed star.

During the process of star formation, some protostars never reach the critical mass required to ignite the fires of nuclear fusion.

VARIABLE STARS A star that changes

in brightness. These fluctuations

can range from second to years depending on the type of variable star.

Stars usually change their brightness when they are young and when are old and dying.

BINARY STARS Is a system of two

stars that are gravitationally bound to each other.

They orbit around a common point, called the center of mass.

It is estimated that about half of all stars in our galaxy are part of a binary system.

SOLARSYSTEM

THEORIES OF THE ORIGIN OF THE SOLAR SYSTEM

1. NEBULAR HYPOTHESIS – for many years the nebular hypothesis was a leading theory. According to it, the sun and its planets supposedly condensed out of swirling eddies of cold, dark, interstellar clouds of gas and dust.

2. FISSION THEORY – the “fission theory says that our sun burst one day, and all our planets came from it. Then the moons shot out from each planet, stopped, turned sideways and began circling the planets they came out of.

3. CAPTURE THEORY – the “capture theory” says that our planet and moons were wandering around in space and the planets were captured by the gravity of our sun, and the moons were captured by the planets.

4. ACCRETION THEORY – the “accretion theory” says that our planets and moons were wandering around in space and the planets were captured by the gravity of our sun, and the moons were captured by the planets.

5. PLANETARY COLLISION THEORY – the “collision theory” of the origin our moon theorizes that our world is said to have collided with a small planet. The resulting explosion threw off rocks which formed our orbiting moon.

6. STELLAR COLLISION THEORY - the “collision theory” of the origin of the entire solar system suggests that our planets, moons, and sun all spun off from a collision between stars.

7. GAS CLOUD THEORY – the “gas cloud theory” of our planets and moons teaches that gas clouds were captured by our sun, which then mysteriously formed themselves at a distance into planets and moons.

KEPLER’S LAWThe Laws of Planetary MotionFirst Law:The orbits of the planets are ellipse with the Sun at one focus of the ellipse.

The sun is not at the center of the ellipse, but is instead at one focus (generally there is nothing at the other focus of the ellipse). The planet then follows the ellipse in its orbit, which means that the Earth-sun distance is constantly changing as the planet goes around its orbit. For purpose of illustration we have shown the orbit as rather eccentric; remember that the actual orbits are much less eccentric than this.

KEPLER’S SECOND LAW:

The line joining the planet to the Sun and planet sweeps out equal areas in equal times, so the planet moves faster when it is nearer the Sun. Thus, a planet executes elliptical motion with constantly changing angular speed as it moves about its orbit. The point of nearest approach of the planet to the Sun is termed aphelion. Hence, by Kepler’s second law, the planet moves fastest when it is near perihelion and slowest when it is near aphelion.

KEPLER’S THIRD LAW

Kepler’s Third Law implies that the period for a planet to orbit the Sun increase rapidly with the radius of its orbit. Thus, we find that Mercury, the innermost planet, (Pluto) requires 248 years to do the same.

THE SUNThe Sun is at the center of our solar system. Sun’s structure consists of from inner to outer elements – core (nuclear fusion), radiative zone, convection zone, photosphere, chromosphere, and corona. Some of the Sun’s features are sunspots (photosphere), solar flares, coronal loops, and prominences (chromosphere and corona).

SUN

THE SURFACE OF THE SUN

The Photosphere The deepest layer of the sun you can see is

the photosphere. The word “photosphere” means “light

sphere”. It is called the “surface” of the Sun because at the top of it, the photons are finally able to scape to space.

The photosphere is about 500 kilometers thick.

By analysing light from the photosphere with a spectrograph, astronomers can tell that the Sun is consist of hydrogen and helium.

THE SUNSPOT Sunspots are cooler regions on the photosphere. Since they are 1000-1500 K cooler than the rest of the photosphere, they do not emit as much light and appear darker . They can last a few days to a few months.

THE CHROMOSPHEREDuring solar eclipse a thick layer can be seen at the edge of the dark Moon. This colorful layer is called the chromosphere (it means “color sphere”). The chromosphere is only2000 to 3000 kilometersthick.

THE SOLAR PROMINENCESSolar prominence refers to a phenomenon astronomically which involves dense ionized clouds of gas, otherwise known as plasma, which comes our from the sun and are detained in place by its magnetic field. They are sculpted into vast loops of arches by magnetic fields over sunspot group.The gas may splatter downinto the photosphere ascoronal rain or erupt intospace.

THE SOLAR FLARES Solar flares are violent explosions in the

chomosphere above sunspot groups; are caused by a release of magnetic energy. They send out bursts of high-energy particles and radiation that can interface with radio communications on Earth when they strike the ionosphere – the electrically charged layer of Earth’s atmosphere.

Flares can endanger astronauts in space.

SOLAR FLARES

THE CORONA When the new Moon covers up the photosphere

during a total solar eclipse, a pearly-white corona around the dark Moon is seen. This is the complex upper atmosphere of the Sun. It has a very high temperature, of one to two million Kelvin. Despite its high temperature, it has a low amount of heat because it is so fragile.

The corona is known to be very hot because it has ions with many electrons removed from the atoms. At high temperatures, the atoms collide with each other with such energy to eject electrons. This process is called ionization.

CORONA

THE INTERNAL STRUCTURE OF THE SUN

THE CORE

The energy of the sun comes from the core innermost layer of the sun. The material in the core is firmly attached and has very high temperature, which is about 15 million degrees Kelvin.

THE CORE

THE CONVECTIVE ZONE

The convective zone of the Sun is plasma-made part. Plasma is a “gas” that conducts electrical currents. The plasma in the convective zone is mainly made up of hydrogen (70℅ by mass), helium (27.7℅ by mass) plus small quantities of carbon, nitrogen and oxygen.

CONVECTIVE ZONE

THE PLANETS

A non luminous celestial body bigger than an asteroid or comet, light up by luminosity from star, such as the sun, is called a planet.

Planets are classified into two, these are terrestrial and gas planets.

TERRESTRIAL PLANETS Terrestrial is derived from Latin word

terra, meaning ground or soil.

Are described as the four planets in the solar system that are closest to the sun, Mercury, Venus, Earth, Mars.

These four planets are composed primarily of rock and solid surfaces.

GAS PLANETS

Jupiter, Saturn, Neptune, Uranus are referred to as Jovian or gas planets.

It is much larger than terrestrial planets and composed mainly of gas and liquid.

MERCURY

The closest planet to the sun. It is a little and infertile planet. It has thousand of impact craters. It has no atmosphere that greatly affects its

surface temperature. It revolves around the sun at an average

distance of about 36 million miles (58 million kilometers), compared with about 93 million miles (150 million kilometers) for earth.

Mercury moves around the sun faster than any other planet.

The density of mercury is slightly a smaller amount than the Earth’s density.

It has less mass than earth.

VENUS

It is the Earth’s “twin” because the two planets are so alike in size.

The diameter of Venus is about 7,520 miles (12,100 kilometers), approximately 400 miles (644 kilometers) smaller than that of the Earth.

It takes about 225 Earth days, or about 71/2 months, to go around the sun once, compared of 365 days, or one year

The mass of Venus is about 4/5 that of the Earth.

Venus has smaller amount of density than the Earth.

A fraction of Venus would weigh a little than an equal-sized part of the Earth.

EARTH

Earth ranks fifth in size among the nine planets.

Its diameter is 8,000 miles (13,000 kilometers).

Earth takes 24 hours to turn completely around on its axis so that the sun is the same place in the sky.

Earth takes 365 days 6 hours 9 minutes 9.54 seconds to round the sun.

MARS

Is the fourth planet from the sun. Named for the ancient Roman god of war Is one of Earth’s “next-doors neighbors” in

space. 4.6 billion years old Mars is about 128,390,000 miles (206,620,000

kilometers) or as much as about 154,860,000 miles (249,230,000 kilometers) from the sun.

It revolves around the sun once every 687 Earth days; this is what they call Martian year.

Martian day is 24 hours 39 minutes 35 seconds long.

JUPITER

The chief of the gaseous giants and second of the greater planets, is the biggest planet in solar system, Jupiter.

Over 11 times the diameter of the Earth and has a mass 2.5 times that all of the planets combined.

It revolves around the sun in a slightly elliptical (oval-shaped) orbit.

It takes 9 hours 56 minutes to spin around once on its axis, compared within 24 hours for Earth.

The density of Jupiter is about ¼ that of Earth.

SATURN

The second largest planet and the second gaseous planet is Saturn.

It rotates faster than any other planet except Jupiter.

Rolls around once only in 10 hours 39 minutes, compared to about 24 hours, or one day, for the Earth.

It takes about 10,759 days, or 29 ½ Earth years, to go around the sun, compared with 365 days, or one year, for Earth.

Has a lower density than any other planet.

URANUS

Is the seventh planet from the sun. The farthest planet that can be seen without

a telescope. It revolves around the sun in an elliptical

(oval-shaped) orbit in 30,685, or 84 Earth years.

Rotates on its axis and it takes 17 hours 14 minutes to spin around once in its axis.

Uranus mass is only about 1/20 as big as that of the largest planet, Jupiter

NEPTUNE

One of the two planets that cannot be seen without telescope.

30 times as far from the sun as in Earth. It goes around the sun once in about every

165 Earth years. Spins around once in about 16 hours and 7

minutes.

PLUTO

Dwarf planet that orbits the sun. It lies on region known as the Kuiper belt. 39 times as far from the sun as Earth is. It come closer to the sun than Neptune’s orbit

for about 20 years. Pluto entered Neptune’s orbit on Jan.

23,1979, and remained there until Feb. 11, 1999

THE MOON The Moon is Earth natural satellite and the fifth

largest satellite in the Solar System. The Moon makes a complete orbit around the Earth

every 23.7 days, and the periodic variations in the geometry of the Earth-Moon-Sun system are responsible for the lunar phases that repeat every 29.5 days.

MOON

PHASES OF THE MOONNEW MOON

The Moon’sunilluminated side is facingthe Earth.

The Moon is notVisible (exceptduring solar eclipse).

WAXING CRESCENT

The Moon appears to bepartly but less than one-halfilluminated by direct sunlight.

The fraction of the Moon’sdisk that is illuminated Iincreasing.

FIRST QUARTER One-half of the Moon appears to be illuminated by

direct sunlight. The fraction of the Moon’s disk that is illuminated

is increasing.

WAXING GIBBOUS The Moon appears to be more than one-half

but not fully illuminated by direct sunlight. The fraction of theMoon’s disk that isilluminated is increasing.

FULL MOON

The Moon’s illuminated side is facing the Earth. The Moon appears to be completely by direct sunlight.

WANING GIBBOUS The Moon appears to be more than one-half but not fully illuminated by direct sunlight.The fraction of the Moon’s disk that is illuminated is decreasing.

LAST QUARTER

One-half of the Moon appears to be illuminated by direct sunlight.

The fraction of he Moon’s disk that is illuminated is decreasing.

ECLIPSEeclipse occur when the Earth, Sun and Moon are in a line. If the Moon is in-between the Earth and the Sun, it blocks the view of the Sun from some parts of the Earth, and its produce a solar eclipse. If the Earth is between the Sun and Moon, the Earth block the light from the Sun before if can get to the Moon. Since moonlight is just the light the Moon reflects from the Sun, this will darken the Moon, and we get lunar eclipse. An eclipse is consist of a darker shadow, or umbra and a lighter region, the penumbra or the lighter shadow.

THE SHADOWSWhether it is the Moon between the Earth and Sun, or the other way around, the phenomenon is basically the same: the body in the middle casts a cone shadow, and if the outer body happens to move into this cone, we have an eclipse.It actually consists of a darker cone, or umbra, where no sunlight reaches, and a lighter region, the penumbra, where only some of the sunlight is blocked.

SOLAR ECLIPSEA solar eclipse occurs when the Moon is directly between the Earth and Sun. this is the most spectacular kind, where the day changes into darkness and one can see the stars in plain day surrounding the dark disk of the Moon.

TYPES OF SOLAR ECLIPSE

1. Total Solar Eclipse occur when the umbra of the Moon’s shadow touches a region on the surface of the Earth.

2. Partial Solar Eclipse occur when the penumbra of the Moon’s shadow passes over a region on the Earth’s surface.

3. Annular Solar Eclipse occur when a region on the Earth’s surface is in line with the umbra, but the distances are such that the tip of the umbra does not reach the Earth’s surface.

LUNAR ECLIPSE A lunar eclipse is a celestial that occurs when

the Earth blocks all or part of the sun’s rays, preventing them from reaching the moon and thus creating a shadow across the moon.

A lunar eclipse can happen between two and four times per year.

TYPES OF LUNAR ECLIPSE1. Penumbral Lunar Eclipse The Moon passes through Earth’s penumbral

shadow. These events are of only academic interest

because they are subtle and hard to observe.

2. Partial Lunar Eclipse A portion of the Moon passes through Earth’s

umbral shadow. These events are easy to see, even with the

unaided eye.

TOTAL LUNAR ECLIPSE The entire Moon passes through Earth’s

umbral shadow. These events are quite striking due to the

Moon’s vibrant red color during the total phase (totality).

TIDESThe word “tides” is a generic term used to define the alternating rise and fall in sea level with respect to the land, produce by a gravitational attraction of the moon and the sun.To a much smaller extent, tides also occur in large lakes, the atmosphere, and within the gravitational forces of the moon and sun.

LUNAR TIDES Tides are created because the Earth and the moon

are attracted to each other, just like magnets are attracted to each other.

The moon tries to pull at anything on the Earth to bring it closer.

The Earth is able to hold onto everything except the water.

DIFFERENT TYPES OF TIDESSPRING TIDES

Spring tides are especially strong tides. They occur when the Earth, the Sun and the Moon are in a line.

The gravitational forces of the Moon and the Sun both contribute to the tides.

Spring tides occur during the full moon and the new moon

NEAP TIDES Neap tides are especially weak tides. They

occur when the gravitational forces of the Moon and the Sun are perpendicular to one another.

Neap tides occur during quarter moons.

THAT’S ALL !!

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