Astronomy week 5 notes
Astronomy week 5 notes ASTR 101
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This 3 page Class Notes was uploaded by Breanab on Sunday February 14, 2016. The Class Notes belongs to ASTR 101 at University of New Mexico taught by Trace Tessier in Spring 2016. Since its upload, it has received 19 views. For similar materials see Introduction to Astronomy in Astronomy at University of New Mexico.
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Date Created: 02/14/16
Lecture 5 The solar system • Our solar system has one star, 8 + planets, more than 120 moons, asteroids, meteoroids, comets, and lots of empty space. • A planet orbits the sun, the body has to sweep the debris in its orbital path • Dwarf planets outside the orbit of Neptune with the similar behavior to pluto, with same tilted plane not in the same elliptical plane as the major planets Questions • What percentage of the total mass of the solar system does the sun contribute? • How is the solar system laid out in space? Spacing between planets? Orbital directions? Scales and perspective • The sun accounts for 99.9% of our solar system’s mass • Spacing between adjacent planets roughly doubles between each planet. Most orbits are roughly circular. • All orbit in the same direction, most in the same plane. Two kinds of planets • Terrestrial o Mercury, Venus, Earth, Mars o Close to the sun, small, mostly rocky, high density, slow rotation, few moons, no rings, heavier elements • Jovian o Jupiter, Saturn, Uranus, Neptune o Far from sun, large, mostly gaseous, low density, fast rotation, many moons, rings, main elements H, He Origin of Pluto • Large member of a class of objects in the outer reaches of the solar system • The Kuiper belt objects o 100’s of small planets found, orbits tend to be more tilted like Pluto’s o possibly leftover planetesimals from solar system formation Questions • What are some of the smaller objects or debris found in the solar system? o Comets, asteroids, meteoroids • What information do they contain that the planets and moons do not? Erosion, geological activity, volcanism, etc. o Solar system debris is unevolved, it gives direct evidence of conditions during solar system formation Solar system Debris • Comets o Short period comets § 50-200 year orbits § orbits prograde, close to plane of solar system § originate in Kuiper belt o Long period comets § Few times 10^5 or 10^6 year orbits § Orbits have random orientations and large ellipticities § Originate in Oort cloud • Oort cloud is a huge, roughly spherical reservoir of comets surrounding the solar system. • A passing star may redirect Oort cloud objects, creating long period comets. • Kuiper belt objects can be redirected by Neptune, creating a short period comet. Question • What causes the tail of a comet? o The comet gets heated up as it gets closer to the sun, being pulled by the gravitational force. o The heat force pushing on the comet and the highly charged particles from the sun (solar wind) creates the tail of the comet. § The tail always points directly away from the sun, the tail is due to gas and dust removed from the nucleus Comet structure • Nucleus: 10 km ball of ice and dust • Coma: cloud of gas and dust around nucleus, about 10^6 km across • Tail: always points away from the sun • Coma and tail due to gas and dust removed from nucleus by the solar wind • Far from the sun, the comet is a nucleus only • Dust tail is the debris from the comet being left behind Comet trajectory • Can be seen just before sunrise and just after sunset Meteor showers • Comets break up when near sun, from the solar wind, evaporation, tidal force • Debris spreads out along comet orbit • Intersection of orbits creates the meteor shower Asteroids • Most in asteroid belt, between mars and Jupiter • How did the solar system form? • What must be explained: o Solar system is very flat o Planetary orbit are nearly circular o Almost all moons and planets rotate and revolve in the same direction o Planets are isolated in space o Terrestrial and jovian planet distinction o Left over junk like comets and asteroids • Nebular theory o Nebula: cloud of interstellar dust and gas about a light year across o Condensing cloud heats up, star forms at center o Conservation of angular momentum makes the solar system flat o As a nebula contracts it rotates faster, becoming a flattened disk o But clumps in rotating gas tend to disperse • Condensation theory o Dust grains act as condensation nuclei, radiates heat to help cool gas causing faster gravitational collapse o Accretion: clumps collide and stick o Gravity enhanced accretion: objects have significant gravity meaning faster growth • Asteroid belt
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