Until very recently, with the advent of light pollution and industrial haze and the climate changes caused by the building of the Aswan High Dam, viewing conditions for astronomy in the Arabian peninsula and Egypt were almost ideal, but those in Mesopotamia were very far from this, with frequent rain clouds and dust storms, particularly at sunset. The ancient Mesopotamian priests were therefore willing to use calculated dates for the first visibility of the New Moon in a way that the ancient Arabian priests were not.

This reluctance to use calculated dates has passed into some Moslem communities, so that in England today some of them keep the New Moon on the calculated day and others must wait until it has been observed - not always easy in Bradford!