FIRST SCIENCE · SECOND CHAPTER · NINTH SECTION · Fifth Article
Fifth Article
This article explains the eclipse that occurs in the greatest source of light, the sun, due to the smaller source of light, the moon; the eclipse that occurs in the smaller source of light, the moon, due to the interposition of the earth; and the interposition of the sun between the moon and apogee; as well as the motions of the apogee, perigee, and the nodes of the moon.
O dear one! It should be known that astronomers have said: This lunar sphere, due to its structure, is dense and dark. When it comes together with the sun, and also at the ascending and descending nodes that occur in its inclined orbit, if it encounters the sun’s path during its journey through the zodiac, the mass of the moon comes between us and the sun, thereby veiling all or part of the sun’s light from us. This is the phenomenon called the solar eclipse (kusūf-i shams). And the darkness that appears on the surface of the sun at that time is actually the color of the moon’s body; during a solar eclipse, the darkening of the sun begins from the west. This is because the moon’s movement toward the west is faster than the sun’s movement toward the west. For this reason, the moon comes from the west, catches up to the sun, and interposes itself between the earth and the sun, blocking it. After this, as the moon passes the sun, due to the speed of its movement, the luminous sun begins to shine again from the west. Since the solar eclipse is formed from the shadow of the moon, the solar eclipse always occurs only at the time of the moon’s conjunction (muḥāq), and never at other times.
The explanation of the lunar eclipse is as follows: If the ascending and descending nodes (zeneb) of the lunar sphere, at the two points opposite each other in the zodiac, that is, at the aforementioned alignments, meet the sun; the earth comes between the two and blocks the way, and the shadow of the earth falls upon the side of the moon facing the sun [54/a]. The light of the sun cannot reach all or the part of the moon upon which the earth’s shadow falls, and the moon remains in its own essential darkness. This is the essence of the phenomenon called the lunar eclipse (kusūf-i qamar). The darkening or beginning to shine of the moon starts first from the east. Because, with the sun’s movement toward the east, the moon, with its movement toward the west, first reaches the western side of the earth’s cone-shaped shadow. The eastern side of the moon first enters the earth’s shadow, and the eclipse begins on the side that first enters that shadow. Similarly, the east of the moon is the first to emerge from darkness, and it is also the first to enter darkness. That is, just as the eclipse on the moon begins from the east, so too does the illumination begin from that side. The reason for the eclipse occurring in this manner is the shadow of the earth, and eclipses always occur during the full moon and full phases of the moon. At other times, eclipses do not occur.
And again, one of the various states that occur in the moon relative to the sun is this: As the sun moves with its mean motion, it always mediates between the apogee point of the moon and the center of the epicycle sphere. Because, when the center of the moon’s epicycle is at its own apogee, if the center of the sun and the center of the epicycle are close to each other at a point in the sphere of the zodiac; then, from that point onward, the descending node of the moon and the movement of its inclined sphere, which is contrary to the rising of the zodiac, and the movement of the moon’s apogee from east to west, and the center of the epicycle, from that point onward, moves from west to east in accordance with the rising of the zodiac. The sun also moves from west to east in the same order at this time.
By Allah’s eternal decree, these two movements—the apogee point of the moon toward the west, and the movement of the center of the epicycle of the carrier sphere toward the east—proceed in such a manner that the luminous sun is always found as an intermediary between the two. And due to this mediation, it follows that the center of the moon’s epicycle sphere is at its own perigee at the times of the two quadratures (tarbī‘) with the sun. At the opposition (istikbāl) [509] and conjunction (ijtima‘) [510] positions, the moon is always at its own apogee. In this case, the center of the moon’s epicycle sphere, in each of its mean revolutions, rises to the apogee twice and descends to the perigee twice. Undoubtedly, all these changes and formations occur “by the will of Allah, the Mighty, the All-Knowing.” (Yā Sīn, 36:38) Exalted is the status of Allah, the Creator and the Wise in His creations. His power is unassailable. He is the Possessor of Generosity, the Owner of all perfect attributes.
Because the apogee and perigee points of the moon move together with its inclined sphere, and the ascending and descending nodes move together with the deferent sphere, their positions in the sphere of the zodiac are not fixed, unlike the apogee and perigee points of the other stars. Rather, they move in conjunction with the movements of the aforementioned inclined and deferent spheres.