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: a Herculis, a fine coloured double star, composed of an orange star of magnitude 22, and a blue star of magnitude 6; 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 r000 determined only 2 are variable .