Globular Cluster M13
Messier Catalog: M 13
Constellation: Hercules
The best-known cluster in the northern sky is a showcase of how globular clusters typically look like. Although the picture was taken with my smallest scope, an 80mm/f7.5 refractor, it captures plenty of the diamond-like stars in the outskirts of the cluster. Click on the picture to see the larger version and mind the small background galaxy NGC 6205 to the upper left!
Globular clusters are part of the oldest structures in the universe which formed shortly after the first ignition of star light. The tens of thousands of stars form a gravitational field that doesn't make escapes impossible, but each star which is thrown out of the cluster by close encounters with other stars will tighten the gravitational ties among the others. That's how these structures survived billions of years...