ASTR 114 Lecture Notes - Lecture 1: Celestial Equator, Interstellar Cloud, Sidereal Time
11 Jan 2020
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Document Summary
Star - a large, glowing ball of gas that generates heat and light through nuclear fusion. Planet - a moderately large object that orbits a star; it shines by reflected light. Planets may be rocky, icy, or gaseous in composition. Moon - an object that orbits a planet. Asteroid - a relatively small and rocky object that orbits a star. Comet - a relatively small and icy object that orbits a star. Solar (star) system - a star and all the material that orbits it, including its planets and moons. Nebula - an interstellar cloud of gas and/or dust. Galaxy - a great island of stars in space, all held together by gravity and orbiting a common center. Universe - the sum total of all matter and energy; that is, everything within and between all galaxies. Light travels at a finite speed (300,000 km/s) Light-year - the distance light can travel in 1 year.
