Relying on Astronomy or Sighting for the Entry of the Month

Question:
He says: Honorable Shaykh, may Allah grant you success. We have a doctor at the university who says that the criterion for the entry of the month of Ramadan is the sighting, but we rely on astronomy to deny the entry of the month. So, is…?

Answer:
It is based on the sighting. If we rely on astronomy, it is not based on the sighting. We rely on the sighting, not on astronomy, because the Messenger (peace and blessings be upon him) commanded us to rely on the sighting. So we do not contradict the command of the Messenger (peace and blessings be upon him). Then, who knows astronomy and masters it?
There must be error among the astronomers; they are not infallible. But there is no error in the sighting. The sighting is the sighting, that is all. Why? One who sees it with the naked eye has no doubt about the sighting. But calculation errs and hits the mark because it is human work. This is one aspect. The other aspect, which is more important, is that the Messenger did not command us to rely on calculation. Yes.