HERCULES, in astronomy, a constellation of the northern hemisphere. Represented by a man kneeling, this constellation was first known as "the man on his knees," and was afterwards designated Cetheus, Theseus and Hercules by the ancient Greeks. Hercules contains a famous globular star-cluster (Messier 13) which is the finest example in the northern hemisphere. The sun's motion through space is directed towards a point in this constel lation.