Are astronomical calculations a valid
means of determining the begining of
Ramadan or Eid?

In the name of Allah the most gracious the most merciful.

We see many people try to justify this
method as being a valid form of
determining the beginning of Ramadan however, when we explore the books of the scholars we see this isn’t the case.

Here are some statements to highlight
this further Ibn Taymiyyah states in Majmu al-Fatawa (132/25):

Indeed we know (due to necessity) that from the religion of Islam to act upon the moonsighting for Ramadan, haij, counting the iddah (waíting period), ila (divorce) or other rulings which are based upon sighting the Crescent based upon the news of one who calculates claiming they have sighted or haven’t is invalid. The
texts which have been narrated from the Prophet (sallallahu alayhi wasallam) concerning this are multiple and indeed the Muslims are unanimously…