DRACO (“the Dragon”), in astronomy, a constellation of the northern hemisphere, mentioned by Eudoxus (4th century B.C.) and Aratus (3rd century B.C.); it was catalogued by Ptolemy, 31 stars, Tycho Brahe, 32, Hevelius, 40. The Greeks had many fables concerning this constellation; one is that when Heracles killed the dragon guarding the Hesperian fruit Hera transferred the creature to heaven as a reward for its services. The planetary nebula H. IV. 37 Draconis is of a decided pale blue colour, and one of the most conspicuous objects of its class.