Messier 13, the Great Globular Cluster, lies in the constellation Hercules. It is also known as NGC 6205 and appears within Hercules’s distinctive Keystone asterism, roughly between the stars Zeta and Eta Herculis.
M13 is a globular cluster: a tightly packed, gravitationally bound swarm of several hundred thousand old stars. It is about 24,000 light-years away and roughly 145 light-years across. Its stars formed early in the Milky Way’s history, making the cluster far older than the Sun and a valuable laboratory for studying stellar evolution.
Edmond Halley discovered M13 in 1714, and Charles Messier added it to his catalogue on June 1, 1764. With an apparent magnitude near 5.8, it may be glimpsed with averted vision under exceptionally dark skies, though binoculars and telescopes show it far more clearly. It is sometimes confused with M3, another celebrated northern globular cluster, but M3 lies in Canes Venatici rather than Hercules.