Callisto
This is where Calista came from. It means "most beautiful." Ok, so Callisto is this priestess friend of Artemis. Zeus takes a liking to her (she's hot) and assumes Artemis's form to seduce her. Then someone (either Zeus, so he wouldn't get caught in an affair, or Hera, because she caught Zeus in an affair) turned her into a bear, which Artemis shot while she was hunting. Zeus turned her into a constellation (Ursa Major), which I'll admit is a nice way to say you're sorry.
In Greek mythology, Kallisto or Callisto was a nymph of Artemis. Her name may have come as a title of the goddess Artemis herself, who was known as Artemis Kalliste or "Artemis the most beautiful." Calisto is also a masculine Spanish and Portuguese form of the Latin name Callistus, which has the same meaning ("Most beautiful").
See Also: Callista, Calista, Calixta