ABSTRACT
Galaxies are external systems; many of them are much smaller than our Galaxy, while others are far larger and more populous. Galaxies are external systems; many of them are much smaller than our Galaxy, while others are far larger and more populous. Active galaxies are galaxies with unusual characteristics. Most active galaxies contain a compact, brilliant and often variable central core, known as an active galactic nucleus. Starburst galaxies are highly disturbed systems in which star formation is proceeding at a furious rate. The galaxies are composed of millions of stars, and the spectra are bound to be something of a jumble, but the absorption lines can be measured easily enough. The nearest really large group is the Virgo Cluster, which contains about 2000 members and is the physical centre of what is termed the Local Supercluster; the average distance from us of the galaxies in the Virgo cluster is 60000000 light-years.
