Cal·lis·to 
(kə-lĭstō)
(kə-lĭstō)n.
1. Greek Mythology A nymph, beloved of Zeus and hated by Hera. Hera changed her into a bear, and Zeus then placed her in the sky as the constellation Ursa Major.
2. One of the four brightest satellites of Jupiter. Originally sighted by Galileo, it is the third largest satellite in the solar system.
[Latin, from Greek Kallistō, perhaps from kallistos, superlative of kalos, beautiful.]