The sky may be perfectly clear and the crescent is seen, or it may be hazy and so it is not seen.

Because the factors that enable sighting cannot be controlled by calculation, it is impossible to determine the moment of sighting through computation. This is why the early astronomers—such as Ptolemy, the author of the Almagest, and his predecessors—did not address the issue at all. Only some later figures, like Kūshyār al-Daylamī and those who followed him, attempted it: noticing that the Sacred Law bases the ruling on actual sighting, they wished to attain that end by mathematics, and thus they went astray and misled others.

Whoever maintains that the crescent cannot be seen unless it is twelve degrees, ten degrees, or the like above the horizon is mistaken. Some observers can detect it at a lower elevation, while others fail to see it even at that height; indeed, it may be visible at midday once it has moved only a slight distance away from the sun. Such people have neither respected sound reason nor understood the revealed Law, and the more discerning experts of their own discipline have censured them for it.

Knowledge of the True Dawn

The question of dawn is similar. Time is divided into day, week, month, and year. A day is known by direct sensory experience, and the lunar month and solar year are likewise determined—one by counting the moon’s cycles and the other by observing the sun. The Exalted says:

“And they remained in their cave three hundred years, and they added nine” (Q 18:25).

That is, three hundred solar years and three hundred and nine lunar years.

As for the week, it has no boundary discernible by sense perception or by reason; it became known only through the prophets’ report that God created the universe in six days and then ascended over the Throne. For this reason God prescribed for the followers of every revealed religion a weekly day of assembly devoted solely to His worship, thereby safeguarding the reckoning of the week.