Is it permissible to use astronomical calculations to determine the beginning of the Islamic months?

Answer

Astronomical calculations may not be utilized to negate an immutable principle of the Shariah. We are under obligation to abide by the commands of Allah Ta'ala. If there is a clash between a Shar'i command and a mundane issue, the Shariah has precedence.

Rasulullah (sallallahu alayhi wasallam) had commanded the commencement of the Islamic month with the sighting of the hilaal (crescent moon), and such sighting has to be established by the reports of reliable, uprighteous Muslims. When these Shar'i requisites have been complied with, then all other conflicting evidence will be set aside.

It should be well understood that Deen is obedience to the commands of Allah Ta'ala. Deen is not the product of rationalism or the effects of our logic and understanding. We may not submit Mansoos Ahkaam to our reasoning and abrogate such laws when we believe that the product of Wahi is in conflict with reason.

Regarding the Islamic months, there exists a Mansoos principle, and that is the actual sighting of the hilaal. The birth of the hilaal and the presence of the moon in its orbit are of no consequence in determining the months. Consider the times of Salaat. Maghrib begins with sunset. The Shariah does not go beyond this simple rule. It only prescribes Maghrib after sunset. The Shariah does not prescribe how we should determine sunset. It does not order Maghrib to begin with the physical sighting of the phenomenon of sunset. Hence, it is permissible to determine sunset by any means in order to commence Maghrib. But since there exists a revealed principle for the determination of the months, it (this revealed principle) may not be abrogated by the use of astronomical instruments to reject the testimony of uprighteous Muslim witnesses to the sighting. Thus such testimony may not be rejected, for such rejection will be the abrogation of a Shar'i principle.