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first midterm notes

2 Pages

Astronomy & Astrophysics
Course Code
Clifford Orwin

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Chapter 1 Our place in the Universe geocentric-ancestors thought we lived in an Earth-centered universe. Planet-large bodies which orbit stars,may be various mixture of rocky,gaseous,icy.1. Orbits stars directly,2 massive enough to be compress them into spherical shapes,3. Must have cleared their orbits. (Pluto is a dwarf planet cuz its orbit is full of objects like comets) Asteroid-rocky Comet-icy Moon- orbits a planet Nebula-a cloud of gas and dust, cud see light emitted by gas & parts where blocked by dust. Place where stars form. Stars form when parts of nebulae crushed by own gravity. Solar sys.-Earth is in it, and it consists of the Sun & objects that orbits it-planets, moons, countless small objects like rocky asteroids and icy comets. The sun is a star in the milky way. Galaxy-a great island of stars in space, containing fr. few hundred million to a trillion or more stars. Earth is at more than halfway from galactic center to the edge of the galactic disk. -some galaxies are isolated, some in groups. Milky way is one of the two largest among 40 galaxies in the local group.Its a huge disk shaped collection of 100 billion stars. -galaxy cluster-groups of galaxies w more than a few dozen members. -supercluster-region which galaxies g. clusters tightly packed. Our supercluster is called Virgo. Universe expanding-avg. Distance bw galaxies are increasing w time. The beginning of expansion is the big bang-14 billion yrs ago. But galaxies dont expand. Nuclear fusion-process which lightweight atomic nuclei smash make heavier nuclei.stars are born.gravity compress material in cloud ,the center becomes dense and hot to generate energy Early universe- only hydrogen& helium.Earth had more-CO2,O2,etc, from stars. We are star stuff. Light years-light fr. Star takes many yrs to reach us, so measure distance to stars in units called light year eg.Sirius,8 light yrs away, the appearance we see it today is actually how it looks 8 yrs ago. Observable universe-portion of entire universe that we can potentially observe.-14 billion light yrs. Voyage Scale-model solar sys.- sun as a grape fruit, jupiter as a marble, earth as ball point (pen). Earth is 15 m away. Solar sys. Is empty, so 300 football fields model. Universe is never static-Earth rotates on its axis once every 24 hrs-sol
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