AST 2002 Chapter Notes - Chapter 15: Spiral Galaxy, Protogalaxy, Main Sequence
Document Summary
Galaxies come in many sizes, colors and shapes. Like with stars, it is difficult to get a complete understanding of galaxies, due to the time spans in which they live. Young galaxies formed much earlier in the universe"s history, and thus can only be viewed from great distances. There are three major types of galaxies: spiral galaxies like the milky way, with prominent disks and spiral arms from which they get their name. They have a noticeable disk, bulge, and halo. Furthermore, spiral galaxies are defined by two components: the disk component and the spheroid component. Spiral galaxies may also be considered barred, or having stars curling away from the bar. Lenticular galaxies, a subtype, lack any bars but are too cool to be considered true elliptical: elliptical galaxies compared to spirals, elliptical are rounder and warmer, and contain less dust. Elliptical galaxies tend to appear in clusters of galaxies, bound by gravity.
