Hercules, in astronomy, a constellation of the northern hemisphere, mentioned by Eudoxus (4th century B.C.) and Aratus (3rd century B.C.) and catalogued by Ptolemy (29 stars) and Tycho Brahe (28 stars). Represented by a man kneeling, this constellation was first known as “the man on his knees,” and was afterwards called Cetheus, Theseus and Hercules by the ancient Greeks. Interesting objects in this constellation are: α Herculis, a fine coloured double star, composed of an orange star of magnitude 2½, and a blue star of magnitude 6; ζ Herculis, a binary star, discovered by Sir William Herschel in 1782; one component is a yellow star of the third magnitude, the other a bluish, which appears to vary from red to blue, of magnitude 6; g and u Herculis, irregularly variable stars; and the cluster M. 13 Herculis, the finest globular cluster in the northern hemisphere, containing at least 5000 stars and of the 1000 determined only 2 are variable.
Hercules
