M 13 – Great Globular Cluster in Hercules

M13 was discovered by Edmond Halley in 1714, and cataloged by Charles Messier on June 1, 1764, into his list of objects not to mistake for comets; Messier’s list, including Messier 13, eventually became known as the Messier Catalog.

About one third of the way from Vega to Arcturus, four bright stars in Herculēs form the Keystone asterism, the broad torso of the hero. M13 can be seen in this asterism 2⁄3 of the way north (by west) from Zeta to Eta Herculis. Although only telescopes with great light-gathering capability fully resolve the stars of the cluster, M13 may be visible to the naked eye depending on circumstances.