 [In the heavens] there are no elements of violent motion, because nothing bends their movement, the place of the sphere remains the same and no new place is taken by it. Therefore, circular movement should be instantaneous, but we observe that some spheres move slowly—such as the sphere of fixed stars—and others fast—the daily movement—and that there is neither violence nor resistance among them. The cause for the different velocities is the difference in nobility (sharf) between mover and movable. (IB-SS-fakhry: 116.13–17)