SCI238 Chapter : Astronamy Lecture Notes 1.docx
19 Jun 2013
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Star a large, glowing ball of gas; generates heat and light through nuclear fusion. Planet a moderately large object that orbits a star; shines by reflected light. (rocky, icy, or gaseous in composition) Moon or satellite an object that orbits a planet: the terms are interchangeable, but artificial objects are always called satellites. Comet a relatively small and icy object that orbits a star. Sun, not when they are much farther away. Solar (star) system a star and all the material that orbits it. Galaxy a great island of stars in space, all held together by gravity and orbiting a common center. Universe the sum of all matter and energy. The universe is expanding from the big bang. Based on the observed rate of expansion, he universe is about 14 billion years old. The expansion continues to this day except where gravity has won : stars, galaxies, clusters.
