Lessons in Astronomy

The following eleven circles display eleven movable heavens: namely, seven proper to the Planets, and called those of the Moon, Mercury, Venus, Jupiter, Saturn; one of the Fixed Stars, which is therefore called the Aplanes and the Firmament; two Crystalline heavens, so called because, since they are ἄναστρα, void of stars, they are transparent in a special manner; and finally one Supreme, itself also called ἀνάστερον and the First Movable.

I say "movable" heavens because Theologians establish a twelfth, and that immobile: namely, the Empyrean heaven, which is the seat of the blessed spirits, and is held to be of a square form externally, because the Holy City described in the Apocalypse is said to be laid out as a square.

To keep the number and order of the Heavens in memory, this distich may be of use:

Since, moreover, a twofold motion is generally observed in the Movable Heavens: one called the First, or Diurnal, common to all; the other the Second, and proper to some or to each; and the former—