AY 101- Midterm Exam Guide - Comprehensive Notes for the exam ( 16 pages long!)
Document Summary
Our place in the universe: planet a moderately large object which orbits a star. It shines by reflected optical light from its host star. Planets may be rocky or gaseous in composition: moon/satellite a rocky or icy object which orbits a planet, asteroid a relatively small and rocky object which orbits a star, comet a relatively small and icy object which orbits a star. It may or may not have a tail: star ~10^6 (1 million) km diameter. Earth-sun: 8 minutes: nebula an interstellar cloud of gas within galaxies. ~10 light years=10^14 km: star cluster a collection of hundreds to millions of stars gravitationally bound (or not) orbiting (or inside) a galaxy. 10 light years=10^14 km: galaxy a great island of billions of stars and gas, all held together by gravity and orbiting a common center. 100,000 light years=10^18 km: galaxy or group clusters a collection of tens to thousands galaxies gravitationally bound together.