art by: http://mictones.deviantart.com/
The zodiacal constellation Sagittarius represents the centaur Chiron. Most of the centaurs were regarded in myth as bestial--they were, after all, half horse. However, the ancient Greeks had a great deal of respect for the horse, and so were reluctant to make the centaurs entirely bad. In fact, Chiron was renowned for his gentleness. He was an excellent archer, musician, and physician, and tutored the likes of Achilles, Jason, and Hercules.
Chiron, however, was accidentally shot and wounded by Hercules. The arrow, which had been dipped in the poison of the Lernaean Hydra, inflicted great suffering on Chiron--so great, in fact, that even the talented physician could not cure himself. In agony, but as an immortal unable to find release in death, Chiron instead offered himself as a substitute for Prometheus. The gods had punished Prometheus for giving fire to man by chaining him to a rock. Each day an eagle would devour his liver, and each night it would grow back. Jupiter, however, had at the request of Hercules agreed to release Prometheus if a suitable substitute could be found. Chiron gave up his immortality and went to Tartarus in place of Prometheus; in recognition of his goodness, Jupiter placed him in the stars (Pasachoff, 139).
From the northern hemisphere, Sagittarius may be seen only in the summer, lying low in the south. The Milky Way runs through Sagittarius.