AY 101 Lecture Notes - Lecture 29: Main Sequence, Open Cluster, Parallax
Document Summary
Galaxies are found in pairs, groups, clusters, and superclusters. The milky way is part of a small gala(cid:454)(cid:455) group (cid:272)alled the (cid:862)lo(cid:272)al group(cid:863) A spiral-poor galaxy cluster; mostly contains elliptical and s0 galaxies. A cluster of galaxy clusters and groups: the largest units of matter known. Consists of all the galaxy pairs, groups, and clusters within about 100 million light years from the milky way. Includes the local group as well as the virgo galaxy cluster. We k(cid:374)o(cid:449) gala(cid:454)ies are far a(cid:449)a(cid:455) (cid:271)e(cid:272)ause (cid:449)e (cid:272)a(cid:374)"t see the i(cid:374)di(cid:448)idual stars easil(cid:455) in most of them. Knowledge of distances is essential for a better understanding of the nature of galaxies. If we know distance we can tell how: luminous, massive, big a whole galaxy is. Measuring galaxy distances is difficult because there is no direct way of doing it. Lookback time: distance in light years of a galaxy when the light we now receive from it left it.
