Callisto (kəlĭsˈtō) [key], in Greek mythology, an attendant of Artemis. Because she forsook her chastity and bore a son, Arcas, to Zeus, she was transformed into a bear by Artemis. According to another legend she was changed into a bear by the jealous Hera. Arcas, while out hunting, was about to kill her when Zeus intervened and transferred them both to the heavens, Callisto becoming the constellation Ursa Major [great bear] and Arcas becoming Arcturus.
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