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Chpt 8,9, 24
The Sun, stars, meteorites, comets and asteriods
| Question | Answer |
|---|---|
| What is the diameter, mass, and composition of the Sun? | Diameter: 109 Earths Mass: 333,000 Earths Composition: 78% Hydrogen, 20% Hellium, 2% Other identified elements. |
| What is the spectral class and visual magnitude of the Sun? | G, A yellow star -26 |
| What elements are present in the Sun? | The whole periodic table |
| What is the Corona? | The sun's outermost atmosphere with low gas density, but million degree temperatures. |
| What shapes the Corona? | The magnetic field, the magnetism heats it to very high temperature, so it shines brightly in short wave lengths. |
| What is the Chromosphere? | Glowing intermediate atmosphere layer composed of gas jets/streamers called spicules and prominences. Temperatures from 4500-100,000C |
| What part of the Sun is red glowing during a solar eclipse? | Chromosphere |
| What is the source of heat of the Chromosphere? | Convection and magnetism. |
| What is the Photosphere? | Visible surface, includes sun spots, granules, plages, and solar flares. Temps 400-6800C |
| How hot do Sunspots, plages, and granules get? | Sunspots: 4500C Plages: 6800C Granules: 5800C |
| What are quiet sun features? | Always present features of the sun. convective features. |
| What are active sun features? | 11 Year cycle, tied to solar magnetism |
| What are sunspots? | Dark spots on the photosphere cooler than the rest of the surface by 1500 degrees. |
| What do sunspots have to do with the magnetic field? | Points where the sun's magnetic field exits and reenters the surface. Each spot with different polarities. |
| How does the Sunspots move? | In pairs called leaders and followers. |
| What is the center and dark area around a sunspot called? | Umbra, penumbra |
| What type of feature are Sunspots? | Active Sun features, come in 11 year cycles |
| What are plages? | Bright areas around sunspots, hotter than the surface and brighter. |
| What type of feature are plages? | Active Sun Features, come in 11 year cycles. |
| What are granules? | Bubble-like/Honeycomb cells found all over the photosphere, restult of convection. The outer edges are falling gas and the cell is rising. |
| What type of feature are granules? | Quiet Sun Features |
| What are solar flares? | Largest explosion in Solar System today, sudden violent outbursts of light and wind particles from sunspot |
| What creates solar flares? | Changes in the magnetic field, field lines are interacting and reconnecting. |
| How much energy is released from a solar flare? | Exceeds billions of hydrogen bombs. |
| Does every solar flare release a CME? | No |
| What are spicules? | Convective gas jets/streamers rising from photosphere, rise and fall within minutes |
| How high can spicules go? | Up to altitudes of 20,000 miles |
| What kind of features are spicules? | Quiet sun features |
| What are prominences? | Large upheavals of gas suspended above photosphere by magnetic field above sun spots |
| What type of feature are prominences? | Active Sun features |
| How high can prominence reach? | Altitudes of 500,000 miles |
| What are the three layers of the internal structure of the Sun? | Core Radiative Convective |
| What is the Sun's Core? | Most center layer such high pressure and temperatures taht hydrogen fuses into helium |
| What is the Sun's Core temperature? | Around 15 million Celcius |
| How can hydrogen nuclei fuse together? | They overcome the coulomb repulsion and fuse together, the fusion only happens in the core. E=MC^2 |
| What is the process of hydrogen nuclei fusing together called? | Proton-proton process |
| What is the Radiative Zone of the Sun? | Light produced in fusion process is transported to the surface, radiation is the dominant form of energy transfer. |
| How long does it take a photon to reach the Sun's surface? | 200,000 years |
| What is the Convective Zone of the Sun? | Last 20% of Sun's interior where energy transfer by convection is dominant. |
| What is the top skin of the Convective Zone of the Sun? | Granules |
| What is the hydrostatic balance? | Sun rises every day about the same size and brightness, only possible due to this balance. Gravity=Fusion |
| What is the Babcock theory? | Active sun features due to the magnetic field and that the sun rotates differently. The different rates cause the field lines to become entangled and wrapped around the sun creating sunspot pairs. |
| How long does it take the poles to rotate? The Equator? | Poles: 40 Days Equator: 27 Days |
| What is Zeeman Splitting? | Strong magnetic field causes spectral lines to break into multiple lines and separate, the stronger the field the greater the separation. |
| What can the Zeeman effect measure? | Field strength of sunspots. |
| What is the Sunspot Cycle? | Every 7-15 years (11 on average) large sunspots with more plages, prominences, and solar flares. |
| What is the Magnetic Cycle? | Magnetic polarity of leader sunspots in each hemisphere will undergo a reversal every 11 years, beginning of new solar cycle, takes 2 sunspot cycles for original polarity to return. |
| How long is the Magnetic Cycle? | 22 year cycle (2 sunspot cycles) |
| What effects does space have on Earth? | High Solar Activity can interfere with radio and satellite communication, bigger more frequent Aurora during high solar activity, Solar flare can trigger an aurora 48 hours later that can lead to utility failure, and weather. |
| What is the Maunder Minimum? | Analysis of sunspot records between 1645-1715 where very few sunspots were visible on the Sun. It stopped it's 11 year cycle and decreased luminosity for 70 year period. |
| How did the Maunder Minimum effect Earth's climate? | Cooled Earth down, mini ice age. |
| What does the Maunder Minimum indicate? | An unknown long term solar cycle. |
| What evidence can you give that granulation is caused by convection? | Doppler measurements show that the center of the granules are rising and the outer part is sinking and the granule centers are hotter than the dark outside. |
| What heats the chromosphere and corona to maintain such high temperatures? | Energy is transported from below outward from the fluctuating magnetic field, which maintains the high temperatures. |
| What evidence can you give that sunspots are magnetic? | The spectral line are split by the Zeeman Effect and observations show ultraviolet material arched from one sunspot to another. |
| How does the Babcock model explain the sunspot cycle? | Magnetic field lines become tangled from the differential rotation of the Sun and it tangles the lines, on average about every 11 years it falls apart and flips to make the lines untangled and smooth again. |
| How can solar flares affect Earth? | Solar flares can interfere with radio and satellite activity and communication weather, it can trigger an aurora 48 hours later, which can lead to utility failure. |
| Why does nuclear fusion require high temperatures and high densities? | Nuclear fusion requires high temperatures and densities to overcome the coulomb force and their electrical repulsion. |
| If a sunspot has a temperature of 4200 K and the average solar photosphere has a temperature of 5780 K, how much more energy is emitted in 1 second from a square meter of the photosphere compared to a square meter of the sunspot? | It emits about 3.6 times more energy in one second. |
| A solar flare can release 1025 J. How many megatons of TNT would be equivalent? | 2,500,000,000 megatons of TNT would be equivalent. |
| Why are Earth-based parallax measurements limited to the nearest stars? | The atmosphere causes a blurring effect on star images. |
| If a star’s apparent magnitude is equal to its absolute magnitude, what must be the star’s distance? | If a star’s apartment magnitude and absolute magnitude are equal then the star’s distance must be 10 parsecs. |
| A star is observed to have no proper motion. What are some possible explanations? | An explanation could be that the star is too far away to detect a parallax shift or that the star is not moving at all. |
| What evidence shows that white dwarfs must be very small? | White dwarfs have a low luminosity, but are very hot stars, which means they must be very small. |
| A star has a spectral class M. What type of star could this be? | This star could be a red supergiant, red dwarf, or red giant. |
| If a star has a parallax of 0.016 arc second and an apparent magnitude of 6.0, how far away is it, and what is its absolute magnitude? | It’s an absolute magnitude of 2 and 62.5 parsecs away. |
| If a star has an apparent magnitude equal to its absolute magnitude, how far away is it in parsecs? In light-years? | It is 10 parsecs away or 32.6 light years away. |
| What is the total mass of a visual binary system if the average separation of the star is 8.0AU and their orbital period is 20 years? | 1.28 Solar Masses |
| Estimate the luminosity of a 3-solar-mass main-sequence star; of a 9-solar-mass main-sequence star. Can you easily estimate the luminosity of a 3-solar-mass red giant star? Why or why not? | The mass luminosity relationship is not useful for red giant stars, 3 solar mass main sequence stars would be 47 luminosity, 9 solar mass main sequence stars would be 2187 luminosity. |
| What powers the Sun? | The Sun is powered by nuclear fusion, converting matter into energy. |
| What is released from a solar flare? | A burst of high energy particles like x rays, and coronal mass ejections are released from solar flares. |
| What happened in Canada in 1989 related to the Sun? | A power surge caused by a coronal mass ejection wave, in less than 2 minutes 6 million people were left without power. |
| What happened in 1859 related to the Sun? How is this important to present times? | A super storm caused by two massive coronal mass ejections waves causing huge auroras and sparking electric power lines. The technology was less advanced and susceptible back then, so a storm like that today would be more catastrophic. |
| What is Helioseismology? | Helioseismology is the study of the vibrations/sound waves of the surface and internal structures of the Sun. |
| What two forces hold the Sun together and intact? | The two forces that hold the Sun together and intact are gravity and hydrogen fusion. |
| What happens in the Sun’s radiative zone? | Energy being transmitted by radiation, photons take the ‘random walk’. |
| What drives solar storms in the first place? | The Sun’s magnetic field drives solar storms in the first place. |
| What is differential rotation and what role does it play on the Sun? | The Sun’s poles spin faster than the equator, this creates the magnetic field in the Sun. |
| What are the names of the three interior layers to the Sun? | The three interior layers of the sun are the core, radiative zone, and the convective zone. |
| What evidence can you give that granulation is caused by convection? | Doppler measurements show that the center of the granules are rising and the outer part is sinking and the granule centers are hotter than the dark outside. |
| What heats the chromosphere and corona to maintain such high temperatures? | Energy is transported from below outward from the fluctuating magnetic field, which maintains the high temperatures. |
| What evidence can you give that sunspots are magnetic? | The spectral line are split by the Zeeman Effect and observations show ultraviolet material arched from one sunspot to another. |
| How does the Babcock model explain the sunspot cycle? | Magnetic field lines become tangled from the differential rotation of the Sun and it tangles the lines, on average about every 11 years it falls apart and flips to make the lines untangled and smooth again. |
| How can solar flares affect Earth? | Solar flares can interfere with radio and satellite activity and communication weather, it can trigger an aurora 48 hours later, which can lead to utility failure. |
| Why does nuclear fusion require high temperatures and high densities? | Nuclear fusion requires high temperatures and densities to overcome the coulomb force and their electrical repulsion. |
| If a sunspot has a temperature of 4200 K and the average solar photosphere has a temperature of 5780 K, how much more energy is emitted in 1 second from a square meter of the photosphere compared to a square meter of the sunspot? | It emits about 3.6 times more energy in one second. |
| A solar flare can release 1025 J. How many megatons of TNT would be equivalent? (See Problem 13 for conversion between megatons and joules.) | 2,500,000,000 megatons of TNT would be equivalent. |
| What do widmanstätten patterns indicate about the history of iron meteorites? | Widmanstatten patterns show that molten metals cooled slowly over millions of years, the iron meteorites are found in the cooling interiors of planetesimal sized objects. |
| What do chondrules tell you about the history of chondrites? | Chondrules show that temperatures of chondrites don’t reach a high enough temperature to melt them. |
| Meteorites were once part of which type of celestial object? | Meteorites were once part of asteroids. |
| A fragment from the surface of a differentiated asteroid will yield which kind of meteorite? | A fragment from the surface of a differentiated asteroid will yield an achondrite meteorite. |
| How many parsecs equal a light year? | 1 Parsec is 3.26 Light Years. |
| What are some nearby stars and how far away are they? | Sirius: 8.57 Light Years Alpha Centauri: 4.4 Light Years Proxima Centauri: 4.3 Light Years |
| What is parallax motion? | The degree to which a star changes its apparent position with respect to distant stars in 6 months. |
| How many times and how far apart are stars measured for parallax rotation. | 2 times in 6 months |
| What is the base of the triangle is radial velocity? | Earth's Orbit |
| What is distance and P measured in? | Distance: Parsecs P: Arc-Seconds |
| At what distance does the parallax technique fail? | 50 Parsecs |
| What is the distance of a star with parallax shift of .1"? | D=1/p D=10pc |
| What is proper motion? | The rate at which a star changes its apparent transverse (side to side) position with respect to background stars in one year. |
| How many times in what period is proper motion measured? | Twice in one year. |
| How does proper eliminate a possible parallax shift? | Measuring at exactly a year |
| What measurement is used to measure proper motion. | Mu, arcseconds |
| Which stars have bigger proper motion number distant or close stars? | Closer |
| What is the star with the highest known proper motion? | Barnard's star: 10.3" per year |
| What is radial velocity? | Motion of a star toward or away. |
| What is radial velocity measured by? | A spectra using the Doppler Effect. |
| What is a red shift? | Spectral lines indicating motion away |
| What is a blueshift? | Spectral lines indicating motion towards |
| What is space velocity? | The complete picture of how a star moves in space. |
| How can you turn proper motion into transverse velocity? | By knowing the distance of the star and using the pythagorean theorem. |
| What is apparent magnitude? | The brightness of a star as it compares to the others in the sky from Earth's point of view. |
| Who made the original scale of apparent magnitude? | Hipparchus |
| How big is the original apparent magnitude scale (Brightest to Faintest) | 1-6 |
| What is the factor difference between each step in the apparent magnitude scale? | 2.512 |
| What is the faintest magnitude seen by a telescope? | +27 |
| What is the faintest magnitude seen by the naked eye? | +6 |
| What is absolute magnitude? | The magnitude of stars as viewed from a standard distance of 10 parsecs. |
| What is the equation for absolute magnitude? | M=m+5-5logd |
| When is absolute magnitude and apparent equal? | At 10 parsecs |
| Sirius: D= 2.61pc, m=-1.5, what is the absolute magnitude? | M=-1.5+5-5log2.61 M=3.5-5log2.61 M=3.5-2.08 M=+1.42 |
| Sun: D=4.852x10^-6, m=-26.8, what is the absolute magnitude? | M=-26.8+5-5log(4.852x10^-6) M=-21.8+26.57 M=+4.77 |
| What star is brighter the Sun: +4.77 or Sirius +1.42? By how much? | Siruis ΔL = 2.512^Δm Δm = 4.77 – 1.42 = 3.35 ΔL = 2.51^23.35 ΔL = 22 times |
| What is the vertical and horizontal axis of the HR diagram? | Vertical: Absolute Magnitude Horizontal: Color/Temperature |
| What is spectroscopic parallax technique? | Using a spectra to find a distance to the star, reaches much further than the Trig parallax method. |
| What can a spectra tell? | Absolute magnitude estimate to solve for d Logd=(m-M+5)/5 |
| What is the distance of a star with M= -10 and m=+10? | M=m+5logd -10=10+5-5logd -10=15-5logd -25=5logd 5=logd d=100,000pc |
| What is the spectral classification of stars (hottest to coolest) | O: Violet B: Deep Blue A: Blue F: White G: Yellow K: Orange M: Red |
| What are other letters for brown dwarf stars? | L, T, Y |
| What are visual binaries? | Two or more stars which seen with a telescope orbit each other over many years, are always seen as two separate bodies. |
| What are astrometric binaries? | Discovered as a result of a proper motion wobble. |
| What are spectroscopic binaries? | In a telescope only see one star, but spectra reveals more than one set of spectral lines. The lines will show doppler shifts as the stars orbit each other. |
| What is a subset of spectroscopic binaries? | Eclipsing binaries |
| Two stars are 12AU with distances to center of mass of 9 and 3AU. Orbital period of 4 years. What is their system masses? What are their individual masses? | M1+M2=D^3/P^2 M1+M2=12^3/4^2 M1+M2=1728/16=108 Solar masses M1(9)=M2(3) 4M1=108 M1=27 M2=3(27)=81 |
| What is stellar rotation? | Rotation of stars creating lines broadening in spectral lines of a star. |
| What kind of stars will show periodic fading as a result of rotation? | Stars with starspots |
| What allows us to observe rotation directly? | Interformeters |
| What are stellar diameters? | Interferometers allow direct measures of stars sizes. Analysis of eclipsing binary star light curves allow size calculation. Timing star occulations by moon's dark side allows size calculations. |
| What particle in space are capable of becoming meteors? | Comet Dust Asteroid Fragments Planetary Impact Ejecta |
| What does the Zodiacal light illustrate? | The abundance of meteoroid material still in the ecliptic |
| What are meteors? | Fiery phenomena observed when a meteoroid particle enters the atmosphere. |
| Where do most meteors burn up? | Ionosphere |
| How many meteors enter the atmosphere daily? How many can you see per hour every night? | 100 ton 10 per hour |
| What is a meteorite? | Fragment found to hit the ground following a meteor. |
| What are the type of meteorites? | Stony 94% Iron 5% Stony-Iron 1% |
| What is differentiated meteorite? | Part of a massive parent body, having been exposed to heat of burial in a parent body and having experienced differentiation. (Iron meteorite core material) |
| What is primitive meteorite? | A tone that is rich in primordial simple compounds including water which were in the Solar Nebula. Chondrules are present in the stone. |
| What is widmanstatten pattern? | A large crystal pattern of metals in an Iron meteorite, the large crystals are the result of very slow cooling in the parent body. |
| What are chondrules? | Spherical grains rich in glassy rock, indicates very fast cooling in only hours. |
| What are annual meteor showers? | Earth passing through the orbit of a comet sweeping up dust. Name after the constellation radiant. |
| What are population I stars? | Younger stars that are more metallic rich. |
| What are population II stars? | The old metal poor stars that form the halo of the galaxy. |
| Where do you find population I stars? | They form the disk of the galaxy. |
| What is the Chandrasekhar limit? | When a white dwarf exceeds a solar mass of 1.4 the balance is unable to be sustained and the star collapses and explodes. |
| What do star death result in? | Supernovae Neutron Star Black Holes |
| Stars | Other Suns. These are self luminous bodies of gases (plasma) shining due to a nuclear energy process, specifically hydrogen fusion into helium. |
| Constellations | Patterns of stars in the night sky, named after animals, hereos, or objects. |
| Planets | Largest nonstellar object found orbiting stars. |
| Comets | Relatively fragile bodies of ice, dirt, and rock, orbiting the sun in long elliptical orbits. Most comet bodies or nuclei are small, less than 20 miles across. |
| Asteroids | bodies of rock, silicates or metals, orbiting the sun.Sometimes called minor planets. Most asteroids are found between Mars and Jupiter in the "Asteroid Belt". |
| Galaxies | Giant islands of stars in the universe. |
| Nebula | Giant clouds of gases and dust in a galaxy. Some clouds are stellar birth places, others are the remains of stars that have died. |
| Voids | Seemingly empty regions edged by the filaments or walls (like the center of a bubble). |
| Transit | When an object crosses the meridian. |
| Altitude | The angular height of a star or object above the horizon. (0-90 degrees) |
| Azimuth | The position angle of an object around the horizon measured with respect to due north (0-359degrees) |
| Precession | The Earth wobbles like a rotating top with a period of 25800 years giving us changing pole star. |
| Latitude | Location north or south of the equator measured in degrees. |
| Longitude | Location east or west of the prime meridian. (0-180degrees E or W) |
| Right Ascension | Longitude for the sky. Units are time, hours, minutes, and seconds. |
| Total Eclipse | Must be New Moon Crossing the Ecliptic Near Perigee Duration of totality is less than 8minutes |
| Eratosthenes Equation | Radius= Distance of Arc/ Angular Seperation C=2πR R=C/2π |
| Ptolemy (100-170AD) | Greek Astrologer and Cartographer Wrote "The Almagest" Publishes Geocentric Universe Model |
| Perihelion | Close to the Sun (Specifically for planets) |
| 1st Law of Motion (Law of Inertia) | Every body at rest or in a state of constant velocity in a straight line will remain in that state unless acted upon by a force. Measurement is mass (kg, slugs) As mass increases so does inertia |
| Causes of Tides | Differential Gravitation Pull (unequal pull) The Earth is an extended sphere so not all points on Earth can be the same distance from the moon. The results is an unequal pull of gravity across Earth. |
| M(1)+M(2)=D^3/P^2 | M: Masses in solar Mass Units P: Orbital period in years D: Orbital distances is AU |
| Second Postulate | All observers will agree on the speed of light in a vacuum regardless of their motion. |
| What would happen if nuclear force didn't exist? | The world would be cold and dark. |
| Absorption or Dark Line Spectra Type | Most colors are present, but dark lines or absorption lines cut through at various wavelengths. |
| Wien's and Stefan's Laws | The hotter the object the more radiation emitted and the shorter the wavelength of peak emissions. |
| Scientific Method | 1. Observations 2. Creation of a tentative model 3. Derive prediction or observational test 4. Perform tests, observational checks, or experiment 5. Validate or reject the model based on the tests |
| Solar System | Star system we live in, includes sun, planets, asteroids, comets, and moons around the planets. |
| Exoplanets | Planets orbiting other stars. |
| The Milky Way | The proper name of our home galaxy. The name given to the hazy band of distant stars we see in the night sky. |
| Universe (The order of Scale): | Everything. 1. Stars 2. Solar System 3. Galaxy 4. Group of Galaxies 5. Supercluster of Galaxies 6. Filaments and voids (superclusters of superclusters of galaxies) 7. Universe |
| Ecliptic | The Sun's yearly path through 12 constellations of the celestial sphere, caused by Earth's revolution around the Sun. (Zodiac) |
| Zenith | The overhead point in the sky. |
| Revolution | The Earth revolved around the sun once per year. (365.25 days) |
| Declination | Latitude for the sky. Degrees north or south of the celestial equator. (+ is north, - is south) |
| Sidereal Day | One Earth rotation with respect to the stars. Star on meridian rotates and returns to meridian, 23 hours and 56 minutes. |
| What is the order of Aristarchus' Model? | Sun Mercury Venus Earth Moon Mars Jupiter Saturn |
| Eratoshenes (200BC) | Computes the size of Earth using geometry and observations of the sun. (The radius, diameter, and circumference) What is Ptolemy's Universe Model Order? Earth Moon Mercury Venus Sun Mars Jupiter Saturn Fixed Stars |
| Isaac Newton (1687) | Develops 3 laws of motion Develops Law of Universal Gravity Inventor of the Reflecting telescope Discovers white light is composed of colors of light |
| Velocity | Rate of change of distanced traveled. V Units: m/s, km/m, mi/s Velocity=distance/time |
| Force | A push or pull imparting acceleration. F Units: Newtons, Pounds |
| The Equivalence Principle | Observers will not be able to distinguish between forces due to acceleration and gravity. |
| Atom | The smallest level of matter that maintains chemical identity. Made of nucleus and electron orbitals. |
| Chemical Elements | The proton number in the nucleus decides element type. |
| Electric Force | Force is created by the charged nature of some matter (Coulomb Force). This force holds an atom together, also holds White dwarf stars against gravitational collapse. |
| What's an example of scattering? | Red lunar eclipse Red Sunsets Blue sky |
| Spectroscopy | Obtaining a spectrum of the object allows composition, radial velocity, temperature, rotational velocity measures, and luminosity class. |
| Which light is the least energetic? | Radio Light |
| Subatomic Particles Create | Gravity and Electric Force (+) Electric force is another force in nature |
| Hierarchy or order of Relevance | Hypothesis Theory Law |
| Which star is the hottest and coolest? | Violet stars are the hottest, red stars are the coolest. |
| Dwarf Planets | Objects smaller than planets but larger than comets and asteroids orbiting the sun in their own independent orbit. |
| Meteors | These are pieces of dust or rock entering the earth's atmosphere creating a brief fiery streak. Also called a shooting or falling star. |
| Superclusters | Clusters of thousands of galaxies. |
| Filaments or Walls | Clusters of superclusters of galaxies |
| Big Bang | The scientific theory for the creation of the universe |
| How do we know the universe is old? | Expansion Rate Radioactive Isotopes Gyro-Chronology |
| Gyro-Chronology | As stars age the spin rate decreases. Compare spin rates of like stars to get universe age. |
| Novae and Supernovae Explosion | Star deaths |
| North and South Celestial Poles | A projection of the Earth's poles out on to the sky sphere. |
| Celestial Equator | A projection of the Earth's equator on to the sky sphere. A half way line between poles. |
| Fundamental Sky Rule | An observer's latitude determines the altitude of the North Celestial Poles above the north horizon, and vice-versa. |
| Nadir | The point directly below your feet. |
| Meridian | A line drawn from due north through the zenith down to due south across the sky. Objects are always always the highest in the sky for the day when they are on the meridian |
| Aristotle (350BC) | Proves Earth is a sphere Introduces a Geocentric Model |
| Geocentric | Earth in the center of the universe |
| What did the Greeks believe? | The Circle was a perfect form All motion in the heavens needed to be circular The heavens were unchanging and perfect Earth was imperfect and changeable |
| What is Aristotle's Universe? | Geocentric Moon orbits Sun Sun and all planets orbit Earth Comets and Meteors are believed to be part of Earth's atmosphere Mercury, Venus, Mars, Jupiter, and Saturn are the only 5 planets. Earth does not move in this model. |
| What is the order of Aristotle's Universe? | Earth Moon Mercury Venus Sun Mars Jupiter Saturn Fixed Stars (Constellations) |
| Aristarchus of Samos (250BC) | Develops mathematical method for measuring distances to the Sun, Moon and Planets Proposes heliocentric model |
| Why was Aristarchus' Model rejected? | Because stars didn't show Parallax shifts and brightness change |
| Hipparchus (150BC) | Complies first star atlas with a magnitude/brightness scale for stars (1-6) Measured Earth to Moon by Aristarchus method Discovered Precession of Earth |
| What must a model of the solar system explain? | The Sun and moon must seem to move only eastward with respect to the fixed stars. Venus and Mercury are always observed close to the sun. Over several months planets will vary in brightness and speed as seen from Earth. |
| Deferent | A major perfect circle which carries the epicycle around the Earth. This creates prograde motion |
| Epicycle | A small perfect circle which carries the planet. This creates retrograde motion. |
| Equant Point | By placing the center of the deferent motion between two equant points, rather than at the center of Earth, will result in the observed changes in brightness and speed for the planet. |
| Copernicus (1543) | Proposes Heliocentric Model |
| What was the order of Copernicus Model of the Universe? | Sun, Mercury, Venus, Earth, Mars, Jupiter, Saturn |
| What was the fatal flaw to Copernicus Model of the Universe? | Circular Orbits |
| What problems does the Copernicus Model of the Universe fix and how? | Retrograde Motion (A Natural Consquence of planets orbiting the sun at different speeds) Venus and Mercury seen only in phases (Since Venus and Mecury are so close to the sun, we only see them in phases) Brightness and Speed Changes |
| Galileo Galilei (1609) | First Person to Use a telescope Works for the Catholic Church as mathematician and physicist Discovers carters, Maria, Sunspots, solar rotation, Rings of Saturn, The Milky Way is stars, 4 large moons of Jupiter, and the phases of Venus. |
| Galileo Galilei (1609) | Publishes "The Sidereal Messanger" Supports Copernicus Model Publishes "The Dialogue" |
| Tycho Brahe (1546-1601) | Naked-Eye Observer Danish Astronomer Establishes observatory on the Island of Hveen Disproves the Ptolemaic and Copernican model |
| Solar Day | One Earth rotation with respect to the sun. Sun is on meridian rotates back to meridian again (24 hours) |
| Circumpolar Stars | Stars that do not set or rise. The North and South polars the whole sky is circumpolar, while the Equator none is. |
| What is LADEE? | A probe that explored the thin atmosphere and reports by astronauts of glowing around sunrise, perhaps caused by charged dust. |
| What is the problem with Fission theory? | The speed of rotation required for the event is unlikely to happen. |
| What is the Fission theory? | The Earth and the Moon was once a single and conservation of angular momentum. |
| What is the problem with the capture theory? | Does not explain the moon's core and there are orbital problems in the orbit is nearly circle. |
| What is the Capture theory? | The moon formed elsewhere in the solar nebula and was later captured by Earth. |
| What is the problem with the Binary co-accretion theory? | The moon's small core and composition is different. |
| What is the Binary Co-accretion theory? | The moon and Earth formed together in the solar nebula as a system and have been together ever since birth. |
| What are the three lunar origin theories? | Binary Co-Accretion (sister) Capture Fission |
| What are cinder cones? | Lunar Volcanoes |
| What are wrinkle ridge? | A hilly terrain in the Maria formed by volcanism |
| What are Riles? | Sinuous valleys on the moon, lava channels. |
| How do you know if the Earth's moon once has a magnetic field? | We know the moon once has a magnetic field because of magnetized rocks on the lunar surface. |
| What are grabens? | Wide valleys near the edges of the Maria. (May be recent formations 50 million years old due to cooling of interior. |
| What's the lunar interior like? | The crust is thin on the near side due to a tidal bulge, the thin crust allows more Maria to form facing Earth. The core is unusually small, (less than 10% of total volume. The core is solid since theres no magnetic field. |
| How can you date the surface? | Absolutely ages are based on radioactive dating. Ages of areas can be based on crater count, areas with the same amount of craters assumed to be the same age. |
| What is the lunar history? | 4.5 b moon's crust solidifys. 4.5-4 b highland cratering is at greatest. 4-3.3 b impact basins form 3.5-3 b the Maria are formed, volcanism ends. Last b major impacts on the Maria. |
| What is the process of crater formation? | A body striking forms a crater 10 times its size, 2 to 3 times the depth. The crater floor rebounds creating a central peak, impact will excavate debris creating secondary craters and ray, only young craters maintain rays. |
| How was Marias created? | Volcanic activity persisted in the areas of impact basins filling them in with lava creating the Maria. |
| What are impact basins? | Huge craters hundreds of miles wide and originally very deep reaching the mantle of the moon. The walls of impact basins are lunar mountain ranges. |
| What is the soil covering a lunar Maria called? | Regolith. a glassy grit. |
| What are lunar Marias? | Dark Volcanic plains, make up 17% of the moon. Only on the near side of the moon, 3 billion years old. |
| What is lunar highlands? | Light colored heavily cratered regions. Make up 83% of lunar surface, about 4 billion years old. |
| What are the main regions of the moon? | The lunar highlands and the marias. |
| What are the general surface features of the Earth's Moon? | Impact craters Mountains formed by impact Volcanic cinder cones Impact basins filled in with lava to create lava plains known as the Maria. |
| Is there water on the Earth's moon? | Polar ice was discovered by Clementine mission in the 1990's and follow up missions confirmed it's existence. |
| What is the Earth's moon atmosphere like? | Trace amounts of Helium, Argon, Hydrogen, and Neon, pressure is basically zero. |
| What is the surface gravity, surface temperature and density of the Earth's moon? | Surface Gravity: 1/6 Earth Density: 3.3g/cm^3 Temp: 243F day -280F night |
| What is the mass, diameter, and composition of the Earth's Moon? | Mass is 1/80 of Earth Diameter is about 22000miles Composition: 60% Silicates 40% metals |
| What is the KT event? | Dinosaurs wipes 65 million years ago, a layer of iridium rich clay was discovered in 1970s seperating the Cretaceous and Tertiary geologic periods. Iridium is found in iron meteorites. |
| What is Kamchatka event? | December 2018 meteor explodes over Bering Sea with a force of 10 Hiroshima atom bombs. |
| What is the Chelyabinsk meteorite? | An object 55ft across enters the atmosphere above Russia Feb 2013, makes an explosion equal to 25 Hiroshima bombs. |
| What is the Tunguska River event? | An asteroid exploded about 8km above the surface of Siberia Caused by an impact of a silicate rich asteroid, no crater was formed, but trees were set on fire and wiped for 30 miles. The blast was equal to a 12 megaton nuclear weapon. |
| Where is the Barringer crater and how old is it? | Winslow, Arizona 25000-50000 years old 1 Mile Across It's an impact of an iron asteroid fragment. |
| What caused the end of the Permian Era? | 250MYA caused by super volcano |
| Where do Earth quakes and volcanic eruptions? | In plumes on the plate or plate borders. |
| What is the Earth's crust made of? | A collection of moving sections or plates, driven by heat loss from within the Earth. The heat is lost along plate boundaries, and in the center of plates where mantle plumes have broke through the crust. |
| What is Catastrophism? | Quick sudden change to the surface of a planet through catastrophy. |
| What is Uniformitarianism? | Gradual change to planet's surface by slow on going processes. |
| What forms the Van Allen Belts? | Particles from the Sun trapped within the magnetosphere. |
| What causes Northern Lights/Aurora Borealis on Earth? | Solar wind particles making it into the magnetic field a ring or two near the polar regions. |
| What does the Earth's magnetosphere do? | Acts as a barrier/shield protecting the surface from dangerous particles, in particular high energy protons. |
| What are the fluids in planetary magnetic field in terrestrial planets? | Fluids are typically iron, nickel and other metals in terrestrial planets. |
| What are the fluids in planetary magnetic field in Jovian planets? | Liquid metallic hydrogen or hydrogen compounds in Jovian planets. |
| What causes planetary magnetic fields? | Caused by electrically conducting fluid rotating at different speeds with depth. |
| What is the interior structure of Earth? | Crust (lithosphere)- Plate tectonics Mantal- Made of magma or lava Liquid core- Source of magnetic field Solid Core- Rich in Metals (7000K) |
| What is Earth's composition and density? | 40% silicates 60% Metals Denisty is 5.5g/cm^3 |
| What is greenhouse heating on Earth? | The greenhouse gases trap heat in the atmosphere, while Earth maintains a careful balance of CO2 through volcanism and removal through plant life. |
| What are greenhouse gases? | Water and CO2 |
| What is the troposphere? | The layer of weather systems. |
| What does Stratospheric Ozone do? | It filters ultraviolet radiation from the sun |
| What are the atmospheric structures on Earth? | Thermosphere (top) Ionosphere Mesosphere Stratosphere Troposphere (bottom) |
| What is Earth's Atmosphere like and whats the origin? | Nitrogen 75% Oxygen 23% Argon 1% Carbon Dioxide .01% Water 1% Origin is from planetary outgassing and impacts. |
| What are the main features of Earth? | Oceans of water Continents and Islands Mountains Active Volcanoes Faulting of the crust Wind blown erosive features Water driven erosive features Water vapor clouds Very few impact craters (200 world wide) Evidence of life visible from Space |
| How much does the oceans of water make up of the Earth? | 75% of the surface |
| What does water on Mars in the past imply? | A thicker atmosphere in the past capable of water temperatures and a pressure able to maintain liquid water. |
| What did Spirit and Opportunity discover (Spacecrafts sent to Mars)? | Evidence of salt rich layered rocks suggesting lakes and oceans in the past. |
| What does Mars Global Surveyor observation suggest? | Oceans at least as large as texas. |
| What would soil samples from Mars suggest? | Minerals only found in water called Hematite concretions. Changes in gullies of crater walls over a few years, result of ongoing water erosion. Also found Percolates (toxic salts) |
| What did the spacecraft MAVEN confirm about Mars? | The lost of atmosphere on Mars |
| What went wrong with Mars? | Internal heat was lost, volcanism ends, magnetic field fades, and solar winds begin erosion of atmosphere. |
| What did ALH84001 find? | Recovered a meteorite from Allen Hills region of Antarctia, the meteorite was created on Mars 4.5 billion years ago and blasted off Mars in an impact 16 million years ago. |
| How long ago did the meteorite discovered by ALH84001 fall to Earth and what did it contain? | 13000 years ago, it contains fossilized life forms and their waste products. |
| What are runoff channels? | Features which resemble dried out rivers. (Evidence for liquid water water in the past) |
| What are outflow channels? | Evidence of catastrophic floods of water in the past. These may have been triggered by volcanism. |
| What are Impact Craters? | Some of the craters are called Splash or Rampart craters; they show evidence of the impact occurring in an area of water ice in the soil that melted during the impact. |
| What is the shape of Mar's moons and how did they come to be? | Both irregular in shape, like an asteroid. Either captured asteroids or Martian crust knocked off. |
| Did Mars once have water? How do we know? | Channels of Mars shows liquid water flowed on Martian surface in the past. |
| What does the thin atmosphere on Mars cause? | Fresh liquid water can't exist, a very salty water can flow at times. |
| What's Mars' ozone layer like on Mars? | There's no ozone layer |
| What are the winds and dust storms like? | Winds 15MPH Dust Storms are 150MPH |
| Is there a magnetic field on Mars? Why or why not? | No global magnetic field due to solid interior. It has patches of a magnetic field. |
| How old is the surface of Mars? | South hemisphere is heavily cratered (4 billion years old) and North hemisphere is volcanic (3 billion years old) |
| Are there active volcanoes on Mars? | Volcanoes are extinct. |
| What is the Tharsis Bugle? What planet is it on? | Dozens of valcanoes larger than anything on Earth. This is on Mars. |
| What is the Olympus Mons? What planet is it on? | Largest volcano in the solar system. This is on Mars. |
| What are polar caps? | Water ice covered with dry ice. |
| What is tectonic features on Mars? | Mar's Canyons |
| What is special about mars? | Mars has seasonal methane changes. |
| What does the thin atmosphere on Mars cause? | Fresh liquid water can't exist, a very salty water can flow at times. |
| What is the atmospheric composition and pressure like on Mars? | 95% CO2, but the pressure is 1% of Earth. |
| What is Mars' surface temperatures like? | -27F during the day, -122F during the night. can be as warm as 60F |
| What is Mars' polar tilt? | 25 degrees |
| What is the density, surface gravity, and composition of Mars? | Density of Mars 3.9g/cm^3. The surface gravity is .4g. The composition is 60% silicates and 40% metals. |
| What is the mass and diameter of Mars? | Mars' mass is 1/10 Earth and diameter is 1/2 Earth. |
| What is Mars orbital period and Rotational Period? | Orbital period is 687 days and rotational period is 24.7 hours. |
| What are the two moons of Mars called? | Phobos and Deimos |
| How does Mars appear through a telescope? | Polar Caps Dark Areas Orange Background A few white clouds Seasonal variations as to size of the polar caps, and darkness of features Two Moons |
| How often is Mars closest, brightest? | Every 27th months |
| How does Mars appear? | The third brightest planet. Red-Orange color. |
| What evidence do we have for a volcanically active Venus? | Magellan probe saw no evidence of eruptions, lightning associated with acid rainfall. Eurpeon Venus Express mission detected sulfur dioxide variations. Recent evidence suggests slow flows like moving ice packs and up to 1600 active small volcanoes. |
| What evidence do we have for a volcanically active Venus? | Pioneer in 1987 detected variations in sulfur dioxide levels and radio noise bursts coming from the surface associated with lightning triggered by ash falls of volcanoes. The burst came from known mountain areas. |
| What are Venus surface features? | About 900 random impact craters (500 Million years old). Tectonic features in the form of Coronae and Tesserae. Shield Volcanoes and lava flow fields, massive volcanos. Mountains result of Volcanism Dunes, Wind, Erosive No evidence of water |
| How do we know water was destroyed and hydrogen was lost to space by solar winds? | Deuterium Abundance in the atmosphere |
| Why did Earth and Venus differ? | Earth is cool enough for rain,Venus' surface temp is extremely hot. removes CO2 from the atmosphere, produce O2. Venus volcanism atmosphere with CO2, the water evaporated, too hot no longer rain on Venus. Hydrogen was lost to space by solar winds. |
| What are ways atmospheres are formed? | Gases delivered to a world through comet or asteroid impacts. Caputered solar wind particles or the result of solar radiation interacting with the soil of a world. |
| What are ways atmospheres are formed? PT 2 | They were accreted directly from the solar nebula. (Jovian) Out-Gassing through geyser or volcanoes. |
| What is greenhouse heating on Venus? | The sun takes 30 percent of the sunlight scattering it so only red and orange reach the surface. The surface absorbs the visible light and reemits infrared which is trapped by the CO2, temperature is 900F instead of expected 100F. |
| What two types of light reach Venus surface? | Red and Orange |
| How much sunlight is reflected and how much sunlight is absorbed on Venus? | 70 percent of sunlight is reflected back into space. 30 percent is scattered so only re and orange light reaches the surface. |
| What causes such high surface temperatures on Venus? | Greenhouse Heating |
| What is the surface temperature of Venus like? | Surface temperature approach 900F, the hottest surface in the solar system. |
| Where does the Sulfuric Acid come from on Venus? | Volcanic Sulfur Dioxide emission (SO2) combining with water (H2O) |
| What are Venus clouds made of? | Sulfuric Acid H2SO4 |
| What is Venus atmosphere like? | Atmosphere is 96 percent carbon dioxide and 4 percent Nitrogen. The pressure is 100 times Earth's pressure. |
| What is Venus' composition and density? | Composition is 60 percent metals, 40 percent silicates. The density is 5.3g/cm^3. |
| What is the closest planet to Earth and by how much? | Venus comes closer to Earth than any other planet. (25 million miles) |
| What is Venus diameter and mass? | 600km, which is smaller than Earth. Mass is .80 Earth's |
| What is Venus orbital period and rotational period? | Orbital Period= 225 days Rotational period=117 days (solar) |
| What does the surface look like of Venus? | No surface features are ever seen because the clouds never part. Can't been seen with an orbiting spacecraft. |
| What does Venus look like in the sky? | Venus is a yellow-white cloud covered planet that appears in phases. |
| How far is Venus from the Sun? | Venus is never more than 46 degrees from the sun. |
| What is the brightest planet seen from the Earth? | Venus |
| What are the properties of a Jovian planet? | no real surface many moons large mass planetary ring systems large diameter low density 2.0 or less Gas composition, largely Hydrogen Short days Long years |
| What are the properties of a terrestrial planet? | solid surfaces low masses small diameters high densities 3.9 to 5.5 metal rich composition thin atmospheres short orbital periods long rotational periods (days) few if any moons No Rings |
| Trans-Neptune objects | Interplanetary Debris Asteriods Comets Kuiper Belt Oort Cloud |
| What are the Jovian planets? | Jupiter Saturn Uranus Neptune |
| What are the terrestrial planets? | Mercury Venus Earth Mars |
| What's the least dense planet? | Saturn 0.7 g/cubic cm. |
| What's the most dense planet? | Earth 5.5 g/cubic cm. |
| What's the equation for density? | Planetary Mass/ Volume |
| What's the order of the planets from biggest diameter to smallest diameter? | Sun 109 Earths Jupiter 11 Earths Saturn 10 Earths Uranus 4 Earths Neptune 4 Earths Earth 1 Earths Venus 1 Earths Mars 1/2 Earths Mercury 1/3 Earths Pluto 2/3 the size of E. moon. |
| Order of Planets from the Sun | Sun Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto (No longer a planet as of 8/2006) |
| What light gets lost in the atmosphere and which light makes it to Earth's surface? | Visible to radio light makes it to Earth's surface, a portion of Ultraviolet rays reach the surface. Xrays and Gamma rays get lost in the atmosphere. |
| List spectrum of waves from highest wavelength frequency to lowest. | Gamma Rays X rays Ultraviolet Visible Infrared Microwaves Radio |
| Frequency | The number of wave cycles passing an observer each second. |
| Trough | Low point of a wavelength |
| Crest | High point of a wavelength |
| What does light seem to be made up of? | Light seems to be made up of electric and magnetic field waves. These two waves oscillate perpendicular to each other. |
| Photons | Particles of Light |
| Tidal Slowing of Earth's Rotation | The flowing of water toward the moon creates friction with the land causing the period of rotation to be lengthened by .002 seconds per century, this is shown in fossil coral. One day the Earth will always face the moon. |
| What does the special theory of relativity explain? | Shows that for an object moving close to the speed of light time will slow down, length will decrease, and mass will increase. |
| The special theory of relativity | E=MC^2 E= Energy M= Matter C^2=Speed of light squared |
| What are examples of plasma? | Comets, Solar Wind, Nebulae |
| Plasma (Ionic matter) | An excess of negative or positive charge |
| What can you not determine with a spectra? | Can not determine transverse or side to side motion with a spectra, waves are not compressed or strech in transverse motion. |
| What causes a red shift? | A light source moving away or receding will be observed to emit light with λo > λrest. The object will seem redder than normal. |
| What causes a blue shift? | A source moving toward an observer will seem to have λo < λrest or appear bluer than normal. |
| Moving Source | In the direction a source of sound moves the wavelengths become compressed since the waves can only move at the speed of sound and the object is moving at some fraction of that speed. |
| Doppler Effect | The change in frequency of a wave in relation to an observer who is moving relative to the wave source. |
| What causes emission lines? | Emission lines are created in the opposite way, electrons move closer to the nucleus emitting light in the process. Light specific to the element. ΔE = hf ΔE = E2 - E1 |
| What causes absorption and dark lines? | Absorption lines result from electron absorbing a photon and the electron moves to a higher orbit. Dark lines appear at the wavelength corresponding to the needed energy to move out. |
| How can you over come Coulomb Force Attraction? | The only way the electron can overcome the Coulomb force attraction is to gain energy, much like a rocket burns fuel to leave Earth's orbit. |
| Kirchoff's Law #3 | A cool low density gas absorbs light at wavelengths specific to the gas. |
| Kirchoff's Law #2 | A hot low density gas emits an emission spectra. |
| Kirchoff's Law #1 | A hot dense glowing object emits a continuous spectra. |
| Emission or Bright Line Spectra Type | Specific wavelengths are present or lit, most of the spectra is dark. These occur at the level of the atom, specifically they are formed as the result of the electrons changing their orbital distance from the nucleus of the atom. |
| Continuous Spectra Type | All colors are present, a continuous blend from one color to the next. The light is generated through the agitation of the atoms and molecules within the substance. |
| What are the spectra types? | Continuous Emission or Bright Line Absorption or Dark Line |
| Stefan's Law explained | Temperature of body increases, amount of radiation emitted increases, so hot objects are brighter. Violet stars are brighter than red stars, all else being equal. The problem with stars is size influences brightness. |
| Stefan's Law | The amount of radiation an object emits is directly proportional to the fourth power of an object's temperature. Radiative flux α Temperature to the 4th |
| Wien's Law Explained | Hotter objects are shorter wavelengths, hot is gamma, cool is radio. Red stars are cooler than blue stars. Since everything has a temperature, everything emits light somewhere in the spectrum, nothing physical can remain hidden in the universe. |
| Wien's Law | The wavelength at which a body emits most of its radiation is inversely propertional to the temperature of the body.(λ(max) α 1 / T) |
| Thermal Radiation | Any body that has a temperature will emit light due to the atomic motion of the matter in the body. (Thermal or Blackbody Radiation, light emitted is heat) |
| Black | All light is absorbed |
| Reflection (Color) | The color of an object reflecting white light depends upon which light is not absorbed by the body. |
| White Light | All colors of the rainbow are present, the full ROYGBIV blend is white. |
| Brightness of a Light Source | As you move away from a light source, it grows dimmer, this is a particle-like behavior. Brightness is inversely proportional to distance squared. |
| Which light/rays cause the highest violent energy events? Which light/rays cause the lowest coolest energy events? | Gamma Rays Radio Light |
| Which light has the most energy? | Gamma Rays |
| What is h in E=hf? | h is Planck's constant |
| Energy of Light | The photons or particles of light carry energy, the energy of a photon depends upon the frequency of light. The greater the frequency the more the energy. E=hf |
| Radio wave Info | Specfic wavelength of radio impacts a wire small electrical currents are set up in the wire. Radio brightness directly correlates with current flow. Brighter, more current receivers amplify this current millions of times. |
| What is a problem with Infrared astronomy? | Heat is a problem, cameras or sensor have to be cooled to very cold temperatures so that the detectors radiate less radiation than they are attempting to detect. |
| Infrared Astronomy | Some wavelengths or infrared reach the Earth's surface and can be detected using infrared sensitive photographic emulsions or electronic detectors. |
| When did Radio Astronomy begin and how? | In 1930 Karl Jansky (a Bell telephone scientist) discovers natural radio emission from the Milky Way while trying to discover source of nuisance static. |
| What are problems with observing from the Earth's surface? | Weather Opacity (Some wavelengths are totally blocked, other are filtered.) Light Pollution (Bright ligths in the big city) Air Glow (Natural emission of light from atmospheric gases) Turbulence (The motion of the air blurs images) |
| Aperture | The size of the main mirror or lens. |
| Objective | The main mirror or lens. |
| Eyepiece | Lens used for viewing objects with eye looking at the object. (You can change the power of the telescope by changing the eye piece.) |
| Field of View | The angular width of sky viewed by the telescope. |
| Resolution | The fineness of detail present in the image. (θ=λ/D) |
| Photoelectric Photometer | A device used to measure the brightness of objects or with the use of standard color filters, the temperature of objects. |
| Spectrograph or Spectroscope | The device that creates the spectrum |
| Charge-Couple-Devices(CCD) | Electronic camera |
| Photographic Plates | Glass black film for photography. |
| Brightness | Determining a standardized magnitude or brightness of an object. |
| Imaging | Viewing the structure and visible light details of objects. |
| What are the types of reflecting telescopes? | Prime Focus Newtonian Cassegrain Coude |
| Difference in image brightness | ΔB = ΔR2 Change in Brightness is change in radius squared. |
| Image Brightness | Brightness is directly proportional to the radius of the objective lens or mirror. |
| Magnification of Telescopes | M= Objective Focal Length/ Eyepiece Focal Length |
| What was the first discovery of cosmology? | Harlow Shapley discoves Globular Star Clusters is asymmetric |
| What does the first discovery mean? | Since the globular's orbit the center of the galaxy it should be symmetric. |
| How far is the center of the galaxy from the sun? | 30,00 light years away |
| What was the second discovery of cosmology? | Edwin Hubble uses Cepheid variables to prove that andromeda nebula is millions of light years away. |
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