BİRİNCİ FEN · İKİNCİ BÂB · DOKUZUNCU FASIL · Dördüncü Madde
**Fourth Article**
This [passage] describes certain conditions pertaining to the moon, which we call “small luminous bodies” in relation to the sun, the greatest source of light.
O esteemed one! Know that astronomers have stated: Among the changing positions of the moon relative to the sun is what they term *muḥāk* [508]. This occurs when it is deprived of light from its surface facing us. It does not occur because the Earth enters between the sun and the moon, casting a shadow; for the entry of the earth between the sun and the moon (*haylūlet al-arz*) is an eclipse, not *muḥāk*.
Another condition occurring in the moon is increase (*izdiyād*). This is due to the moon moving away from the sun, causing the sunlight to appear more abundant on its surface than usual. Another condition is the first quarter (*terbī-i awwal*), where half of the moon’s surface facing us is illuminated by sunlight without being fully mature. And a state of completion is fullness (the full moon). This is the aforementioned light increasing and becoming complete. Another changing state is decrease (*noksan*). This occurs after the full moon, as the moon approaches the sun, causing the sunlight on its surface to diminish progressively. Another condition is the second quarter (*terbī-i sānī*), where half of the moon’s surface facing us remains illuminated even after the fullness. Another state of the moon is when it obscures the sun (causing a solar eclipse). This is the state in which the luminous face of the sun, facing us, is concealed either entirely or partially by the moon. A further condition is non-eclipse (*munḥāsif*), where the Earth enters between the sun and the moon, causing the entire or partial body of the moon to be veiled from sunlight.
The explanation of the aforementioned phases of the moon is as follows: The moon is inherently close to black, a dark indigo color. It is neither sky-colored nor entirely black, but rather like a metallic mirror—dark and dense. It is round; it appears like a bright spinning top. The moon only reflects light that it receives from elsewhere, and it obtains its light solely from the sun. Therefore, half of it facing the sun is constantly illuminated. And if the shadow of the earth does not obstruct between the sun and the moon, this condition continues as described above. Because the mass of the sun is greater than that of the moon, it illuminates more than half of the moon; less than half remains dark.
The Earth’s shadow is conical (*mahrūt*) in shape, ending on the concave surface of the Venusian sphere. In this case, the point where the aforementioned conic shadow touches the zodiacal belt must be tangent. For the center of the sun always reaches the surface of the zodiacal belt within the eccentric spherical zone. Thus, at the time of conjunction (*iʿtimāʿ*), when the sun and moon meet at the same point in a sign, the moon enters between the earth and the sun, with half of its dark side facing us. Half of its illuminated side becomes invisible to us. It is then that *muḥāk* occurs. For the moon, moving swiftly, passes the sun by about twelve degrees and moves away from it. As half of the moon’s luminous face inclines towards the earth, one side appears visible—this is the crescent. This occurs one day [53/b] after *muḥāk*. For the moon moves thirteen degrees in a day and night—as explained above—while the sun moves only one degree during that period. In this manner, the moon moves away from the sun twelve degrees each day. After the crescent, as the moon moves away from the sun, day by day, twelve degrees, the inclination of its illuminated side, with respect to us, increases from the western direction where it is distant from the sun. This is what we mentioned earlier as increase (*izdiyād*).
Thereafter, as the moon moves further away from the sun, its light appears greater to us each night, and when it has traveled a distance equal to a quarter of its orbit—three signs—half of the moon appears illuminated to us. This is the first quarter (*terbī-i awwal*). After that, as the moon moves away from the sun another six signs, it comes to be directly opposite the sun, with us situated between them. Half of the illuminated surface of the moon faces us completely, and it becomes the full moon. This is the completion of those changes. Thereafter, the moon begins to move away from the sun, approaching it again on its left side, and half of its dark side inclines towards us from the western direction. The other half, which remains illuminated, inclines toward the sun from the eastern direction. In this condition, we have more of the moon’s dark side and less of its illuminated side. This is what we mentioned earlier as decrease (*noksan*) in the moon's changes. Thereafter, as the moon approaches the sun, its darkness increases each night until it again occupies a quarter of the celestial orbit between the two. Then, half of it begins to appear illuminated again. This is the second quarter (*terbī-i sānī*). After that, the moon begins to approach the sun again, day by day, and its light continues to diminish. And thus *muḥāk* occurs a second time from its proximity to the sun.
The moon passes through its mansions and signs in this manner, sometimes coming to be on the same side as the sun, and at other times being opposite it. Approximately every twenty-nine and a half days, it approaches and *muḥāk* occurs. Surely all these changes are by “the will of Allah, the Mighty and All-Knowing” (See Yasin 36:38). The Creator, who possesses wisdom in His creations, is the Almighty and Eternal, far removed from all imperfection.