Why Does Ramadan Start at Different Times in Different Places?

Ramadan, the holiest month of the Muslim calendar, starts on Monday in some countries but on Tuesday in others. How is that possible?

The exact timing depends on when local Islamic authorities around the world declare the sighting of the new moon, the astronomical event that marks the start of the observance.

Here’s why there’s so much variation from place to place.

Islamic countries, and Muslims around the world, use the traditional Hijri calendar to mark religious events. Each month of that calendar begins with the sighting of the early crescent moon, and the holy month of Ramadan begins at the start of the ninth month.

These customs go back centuries. But the exact start time of Ramadan varies from place to place because it depends on a range of factors, including who observes the moon and how, and whether the sky is clear or cloudy at the time.

That explains why Saudi Arabia declared that Ramadan would start on Monday after reporting a sighting of the crescent moon on Sunday, but also why neighboring Oman reported the same day that the moon was not yet visible. As a result, the two countries will begin their Ramadan celebrations about 24 hours apart. The authorities in Iran, like Oman, have also declared Tuesday to be the official start of the holy month.

In Southeast Asia, Islamic authorities in several countries said over the weekend that they, too, would observe Ramadan from Tuesday, not Monday, after unsuccessful moon sightings. That gave millions of people across the region, including in Indonesia, the nation with the world’s largest Muslim population, an extra day to prepare.