The outer spheres

Some diagrams of the universe have only one outer sphere, the primum mobile (translated in the diagram at the beginning of this section as "the first moveable"), the sphere that gives momentum to the rest, and turns around once each day.

In the diagram, a crystalline sphere is next included to explain the phenomenon of the precession of the equinoxes, and there is also a final outer sphere, "The empyreal heaven, the habitation of the blessed."