The Great Cluster in the constellation Hercules � also known as Messier 13, or M13 � is considered to be the finest globular cluster in the northern half of the heavens. It�s found in a star pattern called the Keystone � a lopsided square within the constellation Hercules � between the two brightest stars of northern spring and summer, Vega and Arcturus. Follow the links below to learn more about M13.