E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Calisto, daughter of Lycaon, was violated by Jupiter, and Juno changed her into a bear. Jupiter placed her among the stars that she might be more under his protection. Homer calls it Arktos the bear, and Hamaxa the waggon. The Romans called it Ursa the bear, and Septemtrions the seven ploughing oxen; whence Septentrionalis came to signify the north. The common names in Europe for the seven bright stars are the plough, the waggon, Charless wain, the Great Bear, etc.
Boswells father used to call Dr. Johnson Ursa Major. (See BEAR.)