AS101 Lecture Notes - Lecture 1: Milky Way, Interstellar Cloud, Astronomical Unit
Document Summary
There are many kinds of astronomical objects, gaseous clouds, dust, energy and even dark matter in space Star : a large, glowing ball of gas that generates energy through nuclear fusion. Planet: a moderately large object which orbits a star; it shines by reflected light. Planets may be rocky, icy, or gaseous in composition. Moon or satellite: an 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. Star system: a star or stars and all the material which orbits it, including planets and moons, comets and asteroids. Galaxy: a large group of stars in space, all held together by gravity and orbiting a common center. Nebula: an interstellar cloud of gas and/or dust. Cluster: a group of galaxies all held together by gravity. Super clusters form filaments and walls around voids. These are the largest known structures in the universe.
