Astronomy 1021 Chapter 20: Chapter 20 Summary Cosmic Perspective
7 Jan 2012
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Chapter twenty: galaxies and the foundation of modern cosmology: Lives of galaxies connected to the history of the universe: Three major types of galaxies: spiral galaxies have prominent disks and spiral arms, elliptical galaxies are rounder and redder than spiral galaxies and contain less cool gas and dust, irregular galaxies are neither disk-like nor rounded in appearance. Spiral galaxies tend to collect in groups that contain up to several dozen galaxies, elliptical galaxies are more common in clusters of galaxies that contain hundreds to thousands of galaxies all bound together by gravity. Radar ranging: a method of measuring distances within the solar system by bouncing radio waves off planets.
