DRACO ("the Dragon"), in astronomy, a constellation of the northern hemisphere. The Greeks had many fables concern ing this constellation ; one is that when Heracles killed the dragon guarding the Hesperian fruit, Hera transferred the creature to heaven as reward for its services. The star 7 Draconis has ac quired historic interest because from his observations of it Brad ley discovered the phenomenon of aberration of light (see ABERRA TION). It enjoyed this distinction because it chances to be the brightest star that passes close to the zenith of Greenwich, so that errors of observation arising from refraction are minimized.