Ramadan is not uniformly observed globally — the start date can vary by country or even be different mosque to mosque in the same city for a variety of reasons. But it all starts with a sighting of the crescent moon.

The holy month of Ramadan is expected to begin either today or over the weekend once the crescent moon is seen, with millions worldwide waiting to find out

Deep in the Saudi Arabian desert, a group of robed men are peering into the sky, trying to spot the crescent moon that signifies the start of Ramadan.Their work is significant: an official sighting of the moon begins a month of fasting and prayer for millions of Muslims in Saudi Arabia,