AST 301 Lecture Notes - Lecture 40: Elliptical Galaxy, Spiral Galaxy, Supercluster
Document Summary
Hubble classified them according to texture of their spiral arms and relative size of their central bulges. Sa galaxies have smooth, broad spiral arms and the largest central bulges. Sc galaxies have narrow, well-defined arms and the smallest central bulges. Classified the same way as spiral galaxies. Sba galaxies have the smoothest spiral arms and the largest central bulges. Sbc galaxies have narrow, well-defined arms and the smallest central bulges. Hubble classified elliptical galaxies according to how round or flattened they look. A round galaxy is e0 and the flat galaxies are e7. Most galaxies are about the same size, except for the giant and dwarf ellipticals. Dwarf ellipticals are more common and transparent. They are composed mostly of old stars that are characteristically red. Larger the spread in velocity the brighter the galaxy. If you can get the spectrum for a galaxy you can find the distance. Milky way, andromeda, m33 are major galaxies.
