Moon · a Light

They ask about the crescents and the answer is about time

When people asked the Prophet ﷺ about the phases of the moon, Surah al-Baqarah gave an answer about function rather than astronomy: they are timings for people, and for the Hajj. The moon returns to the same phase every 29.53 days on average, which is why Islamic months run to 29 or 30 days and never to a fixed number. Whether the new crescent can actually be seen on a given evening depends on how far the moon has moved from the sun, how high it sits when the sky darkens, and how clear the air is, and astronomers have published visibility criteria for exactly this. Communities still divide over whether to sight it or to calculate it, and the calculation is not in dispute.

Surah al-Baqarah 2:189

Source · Qur'an 2:189