Callisto was a nymph (or, according to some sources, the daughter of Lycaon) who was associated with the goddess of the hunt, Artemis. Zeus placed Callisto in the sky as the constellation Ursa Major, or “great bear,” and then took Arcas and placed him in the sky near his mother as Ursa Minor, the “little bear.”

Callisto is a moon of Jupiter. It’s the third largest moon in the solar system.