Whether Ramadan has ended depends on whether the new crescent has been seen, and since visibility depends on where you are standing, neighbouring countries regularly celebrate Eid on different days.

Some authorities require a naked-eye local sighting, some accept a sighting anywhere in the Muslim world, and some now use calculated visibility. All three are defensible readings of the same instruction. It is the largest live example anywhere of a religious calendar that is still settled by somebody going outside and looking.