Callisto

in Greek mythology, an Arcadian nymph. Zeus admired Callisto and the jealous Hera changed her into a bear. Callisto was very unhappy in this new form. She was afraid of the other wild beasts, even of other bears, and she was lonely. At last she saw her own son, Arcas, approaching. She sprang forward to embrace him; but Arcas, not recognizing his mother, was about to slay her with his spear, when zeus in pity snatched them up, and changing Arcas too into a bear, set them both in the sky, where they formed the constellations of the Great and Little Bear. Hera was incensed that such an honor should come to Callisto as a result of her punishment. She went to Tethys and Oceanus, who ruled the ocean, and begged them to help her. They could do little, but they forbade the Great Bear and the Little Bear to come into their waters. So these two constellations move round and round in the heavens; but never sink, as do other stars, below the ocean.

There is considerable diversity in the stories of Callisto told by different writers. The foregoing account is Ovid’s version of the tale. According to others, Callisto was an attendant of Artemis and was changed by her into a bear, and her son given to Maia to bring up. Another story is that Artemis herself killed the bear Callisto, and that she was transplanted to the skies as the constellation of the Great Bear, while Arcas was changed to Arcturus in the constellation called Bootes, or the Watcher of the Bear. This is consistent with the story of Cynosura, who was transformed into the Little Bear.

Milton in II Penseroso alludes to the fact that the constellations of the Bear never disappear below the horizon:

See Cynosura