BİRİNCİ FEN · ÜÇÜNCÜ BÂB · DÖRDÜNCÜ FASIL · Üçüncü Madde
**Article Three**
Concerning the established limits of night and day and their respective durations.
Know, O favored one! According to astronomers and mathematicians, a day, encompassing both night and day, is the time it takes for the luminous sun to depart from its meridian circle and, through universal motion, return to that same point within the cosmos. In common parlance, a day – consisting of night and day – is the duration from the setting of the sun until its reappearance at the same location.
It is permissible to consider the beginning of a day and night as commencing with the departure of the luminous sun from any point on the zodiacal belt (manzil al-buruj). However, astronomers [70/a] prefer to mark it from the meridian circle, for the differences in their degrees, measured by rising and setting, are numerous. But with respect to the meridian circle, the difference in degree of the zodiacal sphere is equal at every latitude, as the meridian circle is one of the horizons in all regions.
The duration of a day and night corresponds to the amount the luminous sun traverses westward across the zodiacal sphere during its universal revolution within that time interval. The duration of daylight, according to mathematicians, is the time elapsed from sunrise to sunset.
According to religious scholars, the duration of daylight is the time from the emergence of the second dawn – as mentioned in a preceding article – until sunset. Consequently, according to both viewpoints presented above, the duration of night is not concealed; it is simply the remaining portion of time after defining daytime.
Furthermore, mathematicians have divided each of these defined day and night into two categories: equal hours (sa’at al-mu’tadila) and unequal hours (sa’at al-zamaniyya). Since the quantities of the equal hours are initially equal, they are also called “equal hours.” Each of these equal hours corresponds to the amount of fifteen degrees traversed by the universal motion.
As for the quantities of the unequal hours (sa’at al-zamaniyya), they vary with the changes in the lengths of day and night, so they are also termed "variable hours" (sa'at al-muavwace). However, these unequal hours always constitute one-twelfth of the day and night. If daylight is longer than nighttime, then the hours of daylight are longer than those of nighttime; if daylight is shorter than nighttime, its hours are shorter than those of nighttime. From these explanations, it becomes clear that while the lengthening or shortening of daylight alters the equal hours (sa’at al-mu’tadila), their durations and proportions remain constant – always fifteen degrees. Conversely, the durations of the unequal (zamani) hours change with the lengthening or shortening of daylight, but their number remains fixed at twelve.
Mathematicians have relied on the variable hour (sa'at al-zamaniyya) in matters pertaining to the influences of the stars, and they rely on equal hours (sa’at al-mu’tadila) for other tasks. The numbers and divisions of equal and variable hours (sa’at al-muavwace) are equal at times when night and day are equal.
“We glorify Allah, who turns back nights and days, hours and seasons.” [526]