URSA is the first word of the name of the constellation Ursa Major, or the Great Bear, also known as the Big Dipper, which dominates the North Pole. It never goes below the horizon. In mythology the Great Bear is the huntress Callisto, whom Juno, through jealousy, changed into a bear because Jupiter loved her. When Jupiter set her in the heavens as the Great Bear, Juno decreed that the constellation would never set (Met II.407-530; OM II.1365-1694).

Boethius remarks that Ursa is never washed in the deep western sea; that is, the constellation never sets, Bo IV, Metr 6.8-15. [Arctour: Boëtes: Calistopee]