Astronomy Week 6 Notes
Astronomy Week 6 Notes ASTR 1000-002
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This 6 page Class Notes was uploaded by Jenna Notetaker on Tuesday October 4, 2016. The Class Notes belongs to ASTR 1000-002 at University of Colorado at Boulder taught by Charles Danforth in Fall 2016. Since its upload, it has received 6 views. For similar materials see The Solar System (Lecture) in Astronomy and Physics at University of Colorado at Boulder.
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Date Created: 10/04/16
Astronomy Week 6 Comparative Planetology patterns and trends in the solar system are most important Sun 99.8% of mass in SS Mostly H and He, Traces of other elements Nuclear fusion in core is source of energy Light comes from photosphere (“surface”) Relative sizes: Sun is 10x diameter of Jupiter Jupiter is 10x diameter of Earth Earth is 10x diameter of Pluto 10x diameter = 103 =1000x volume = 1000x more massive (very approximately) SS pattern #1: Orderly Motion All large bodies are in nearly circular orbits, in nearly the same plane (the ecliptic), in the same direction (counterclockwise when viewed from the north). Rotation and moon orbits also CCW. Mercury Looks like the Moon because it is like the Moon. No atmosphere, many craters Rock and metal, large iron core, Rotates 3x for every 2 orbits (tidal locking w/ Sun). Very hot day side, very cold night side. Venus Nearly identical to Earth in size, composition Surface hidden by clouds Extreme greenhouse effect (even hotter than Mercury) Spins backwards (very slowly) Earth/Moon Similar in size/composition to Venus Only planet with liquid water on surface Only planet with life (that we know of) Surprisingly large moon Mars 1.4 AU. About half size of Earth Thin atmosphere, giant volcanos, canyons, polar ice caps Once had liquid water (river channels, layered rocks, shorelines) Moststudied planet (7 current missions) Two tiny moons (captured asteroids) Asteroids Fill gap 24 AU from Sun between Mars and Jupiter Failed planet? Orbits not uniform, planar, circular A few large ones, millions of tiny ones, largest is Ceres (about 1/3rd of the mass) Jupiter 300x mass of Earth 5 AU from sun (much farther than inner planets) Mostly H and He gas (no solid surface) Many moons and rings Huge storms and cloud bands Galilean moons (Io, Europa, Ganymede, Callisto) almost planets on their own Saturn Gas giant like Jupiter (10 AU from Sun, 90x mass of Earth) Spectacular rings from tidal disruption event, many moons Titan has thick atmosphere, hydrocarbon lakes, rivers, clouds Uranus 20 AU First new planet (discovered 1781) Much smaller than J/S but still 15x mass of Earth H/He gas, but also water, ammonia, methane, etc. (“ice giant”) Extreme axis tilt (980) Neptune 30 AU Discovered 1846 Very similar to Uranus in size, composition Large moon Triton orbits backwards (captured KBO?) SS Pattern #2: two (three?) kinds of planets Terrestrial (rocky) planets small, rocky, close to sun, no moons (mostly) Jovian (gas giant) planets large, gas balls, far from sun, many moons, rings ! [KBOs (ice balls) very small, icy objects like Pluto far from Sun] Pluto 3040 AU (1930) Elliptical, inclined orbit (not part of orderly motion) Not a gas giant nor a terrestrial planet something new? Moon Charon is very large First, largest member of the Kuiper Belt Comets Small bodies like asteroids, but mostly made of ices Appear in inner SS occasionally but mostly reside in outer SS Some are from Kuiper Belt, some are from farther out Oort Cloud 100100,000 AU from Sun SS Pattern #3: two kinds of small bodies (rocky, icy) in three different zones (asteroid belt, Kuiper belt, Oort cloud) SS Pattern #4: exceptions to all the rules Orbits: Triton (backwards), small bodies (elliptical, inclined) Rotations: Venus (backwards), Uranus, Pluto (sideways) Moons: Charon, Moon (relatively big); Titan (thick atmosphere) Our theory of SS formation must be able to account for all four of these patterns All things orbit the same direction and relatively circular orbits There are Jovian and terrestrial planets and Kuiper belt objects (planetoids) Pluto is not a planet because there are too many objects similar to Pluto The International Astronomical Union names planetary objects Planets Orbit the Sun Big enough so that its spherical Cleared its orbit Cleared orbit there are no other larger objects that share the orbit Dwarf Planets Orbit the Sun Big enough to be spherical Has not cleared its orbit Comets small icy objects and have very elliptical orbits Oort cloud not observed but inferred Oort clouds from other stars my overlap The number of protons in an atom determines what the element is The universe is composed of 90% hydrogen, 8% helium, and 2% everything else The big bang dispersed hydrogen and helium The other 2% was made in the cores of stars Stars come in different masses The Sun produces hydrogen and helium Massive stars create: H He C, N, O Ne … Fe Fe (iron) cannot burn so when the star gets an iron core it explodes to form a supernova Galactic recycling the cycle all stars go through Star formation observing many stars to find the pattern between all of them Nebula cloud condenses into a star Nebular theory Gas cloud compresses Gravity cause nebula to contract, heat, and spin Flattens into a disk Collisions between particles average out motions and orbits Protoplanetary disk Uniform circular motion Everything is moving very slowly with respect to each other Particles remain close for a long time
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