Calculations, or Follow Saudi, or Moon sighting
by Prof. Gul Agha, USA
..Since the cycles of the moon are easy to compute, it seems silly to rely on sightings. However, even with the use of astronomical calculations, it is not the case that the celebration would fall on the same day in every country, as I recall the rule used is that the sighting should be within some small interval after sundown (someone may have more precise knowledge about this), and this will vary over time zones which are spread over a 24 hour cycle that the earth takes for its rotation. Someone would have to change that rule (and many Islamic theological interpretations would not allow anyone to do that)…