PCS 181 Midterm: Astronomy Midterm Notes
Document Summary
Moon orbits a planet (sometimes called a satellite) Asteroid relatively small rocky object orbiting a star. Comet relatively small icy objects orbiting a star. Galaxy a group of stars clumped together (by gravity) held together by gravity. Groups of galaxies smaller amount of galaxies held together by gravity. Galaxies groups of stars (~ 100 billion stars in each) Solar system planets, asteroids, comets revolving (orbiting) around one star. Earliest matter was created in the form of plasma (resembles both gas and liquid) ~ 1 thousandth of a second (10-3 s) Plasma expanded and cooled forming the building blocks of matter: protons, electrons, and neutrons. Universe cooled considerably creating hydrogen and helium (gases involved in star formation) ~ 800 million years (8 x 108 yrs) Gravity began to hold groups of stars together which formed galaxies. ~ 2 billion years (2 x 109 yrs) Half of the stars we see today were formed organizing themselves into galaxies.
