BİRİNCİ FEN · İKİNCİ BÂB · DOKUZUNCU FASIL · İkinci Madde
Behold the radiant orb of the moon, its sphere a carrier globe, revealing the structure and motion of the celestial realm.
Know then, esteemed one, that astronomers have declared: The third sphere of the moon is this carrier globe, which, as has been explained in preceding discussions, is a globe situated off-center, just as the other planets are positioned within their own globes centered off-axis. And this carrier globe itself resides within an inclined globe. Its exterior convexity touches the exterior convexity of the inclined globe at a point called the "ascension point," while its interior concavity touches the interior concavity of the inclined globe at a point known as the "descension point." The center of this sphere lies beyond the center of the universe by a distance equal to ten degrees and a quarter degree from the ascension point.
When the inclined sphere separates from the carrier globe, two globes remain within it, which are called the “completers of the inclined sphere.” Besides the three courses of motion mentioned earlier [52/b], the carrier globe also rotates within its inclined globe around its own center. This rotation occurs along a belt that is tangent to the inclined sphere and upon an axis parallel to its own, moving from west to east. It traverses more than twenty-four degrees in a day and night, akin to the rising of the constellations. During this motion, it carries with it the epicycle of the moon. For its movement of approximately eleven degrees westward, which is aligned with the rising of the constellations, is countered by the westward movement of the node point and the inclined sphere, acting as an opposition to it, thus returning it.
Thus remains a daily motion of roughly thirteen degrees for the carrier globe of the moon, in accordance with the rising of the constellations. Its movement is swift, its own sphere small, and encompassing the moon, which appears to those on Earth. It lingers within each of the twelve constellations for approximately two days and three-quarters, completing one revolution in twenty-eight days. As it revolves in this manner, it catches up with the sun every twenty-nine and a half days, coinciding with it. This is why lunar months are counted as either twenty-nine or thirty days. The new moon appears to those inhabiting the northern hemisphere during the solstices of summer and winter (June 21st and December 21st) at sunset. For those living near the equator in the southern hemisphere, the moon is easily visible in every season, for the daily turning points of the sun are inclined in the northern hemisphere. In the southern hemisphere, light is received at a more perpendicular angle. Therefore, the moon does not set with the sun; it remains visible above the horizon.