Globular Cluster M13 Imaged by Chris Thayer

M13, the Great Globular cluster in Hercules (also designated NGC 6205)  is easily the best known globular cluster in the Northern celestial hemisphere.   Globular clusters are spherical compact gravitationally bound clusters of stars. There are about 160 globular clusters in our Galaxy and they contain some of its oldest stars – their compactness helps them to survive against disruption by external gravitational perturbations. These clusters are distributed throughout the visible halo of our Galaxy, filling a roughly spherical volume which rotates slowly compared with the disc.  We see no evidence of globular-cluster-sized star clusters forming in our Galaxy. This suggests that the conditions that led to the formation of globular clusters in our Galaxy were quite different from the current conditions.