For the same reason, the dawn interval grows longer in winter, whereas in summer it becomes shorter, because the rays appear later when there is no vapor to reflect them—the summer air being relatively dry. Conversely, the share of the ʿIshāʾ twilight is shorter in winter, for the abundance of vapor then quickly returns the sun’s trailing light. In short, the length or brevity of each of these two intervals is governed by vapor, not by any celestial factor.

Those who supposed that the phenomenon is produced by the motion of the heavens measured it accordingly and erred in their reckoning. They concluded that the dawn interval in winter is shorter than in summer and that the ʿIshāʾ interval in summer is shorter than in winter, arguing that the former is part of the night and the latter part of the day and must therefore match the length of its respective host. They failed to distinguish between the rising and setting of the sun itself and the appearance of its rays: the sun’s body moves in the celestial sphere and is carried along by it, whereas the ray depends on the air and the vapors that bear and reflect it—an earthly cause, quite unlike the motion of the heavens.

Because their conclusion rests on a faulty analogy, sense-perception contradicts them, and the falsity of their claim is recognized by people everywhere. What is confirmed by direct observation and sound reason can never conflict with revelation, intellect, or the senses, for truthful proofs do not contradict one another; disagreement arises only from corrupt analogy and erroneous conjecture.

There is no proof that the number of celestial spheres is nine:

The assertion that there are nine spheres is not established fact, nor is there any evidence that nothing lies beyond them. Their own leading authorities concede that additional bodies may exist. They arrived at the figure of nine solely by observing the differing motions of the heavenly bodies, and in the same way they assigned to each of the five wandering planets several spheres to account for its irregular movements. They judged the elevation of one sphere above another from the lower’s eclipsing of the higher, yet among them there is extensive disagreement—too long to detail here—about astronomical matters that cannot be verified by the senses, and much of what they affirm lacks any proof.

Accordingly, when the prophets spoke of the Lord’s Throne (ʿArsh) and His Footstool (Kursī), some imagined that the Footstool was the eighth sphere and the Throne the ninth—an opinion for which there is absolutely no evidence, and which is