The cosmological system of Ursus is similar to that of Tycho Brahe. Both place the Earth in the center, and set the other planets revolving around the Sun. For Ursus, in contrast to Tycho, the Earth rotates around its axis once a day, allowing the sphere of stars to stand still. If the region of the stars is not a rotating sphere, then stars might be positioned at immense and various distances from the Earth. Ursus’ system, adopted by William Gilbert and others, remained a prominent rival to the Tychonic into the 17th century.