The Great Cluster in Hercules, M13
by Rob Gendler
This globular cluster of stars is one of the most impressive in Earth's skies. Located 25,000 light years from Earth, it contains millions of stars. Astronomers have found that stars, like people, tend to be social and congregate in groups (clusters.) Globular clusters are brighter, more massive, and older than open clusters like the Pleiades.