One of
Jupiter's moons, and the farthest from the planet. Its largest impact dent is named
Valhalla, and another, smaller dent is named
Har. A yet smaller one is named Arthur. (no, not really).
According to Hesiod Callisto was a nymph; she was also known as a companion of Artemis, who shot and killed her for not retaining her virtue. She was turned into a bear by Zeus.