AST 2002 Lecture Notes - Lecture 1: Observable Universe, Interstellar Cloud, Astronomical Unit
Document Summary
Chapter 1: a modern view of the universe. 1,000,000,000,000 = trillion = tera = 1012: metric system. A light-year: the distance light can travel in one year. 1 light year (ly) is about 10 trillion km (6 trillion miles) 1 astronomical unit (au) is about 150 million km: 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. In order to be a planet, an object needs to: orbit a star, be large enough to be round (gravity, pluto is not a planet because: It is too small to be a planet. It has not cleared its orbital neighborhood of other objects. Its composition is not planetary: moon (or satellite) A relatively small and rocky object that orbits a star: comet.
