Can a new moon be calculated precisely?

What can be calculated exactly is where the Moon is in the sky at any given time.

‘New Moon’ is the moment when the Moon comes in its orbit just between the Earth and the Sun. If the three celestial bodies are then exactly in line, the Sun covers the Moon in front of us, so we see the Moon ‘in negative’. When the Moon is above or below the Sun, we see nothing.

What is important for the Muslim calendar is not ‘New Moon’, but the first moment after New Moon when you can see the Moon again. So there is a subjective aspect to this – one sees better than the other – and also a place-related aspect (see below). And of course no one wants a party to be postponed because it is raining.

It is more or less possible to translate that first moment into ‘so many hours after New Moon’, and that can then be calculated perfectly. But it depends on location. Closer to the equator, the moon’s orbit makes a greater angle with the horizon: a thin crescent moon can be seen higher above the horizon and therefore better in Mecca than in Brussels. And there are already differences between Mecca, Medina and Cairo, so that a certain arbitrariness also occurs within the classical Muslim world.