Why does Ramadan start at different times and 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 announce the sighting of the new moon, the astronomical event that marks the start of the celebration.

This is why there is so much variation from place to place.

The base

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 beginning 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 number 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 Ramadan would start on Monday after reporting a crescent moon sighting on Sunday, but also why neighboring Oman reported the same day when the moon was not yet visible. As a result, the two countries will begin their Ramadan celebrations approximately 24 hours apart. Authorities in Iran, like Oman, have also declared Tuesday the official start of the holy month.

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

‘A challenging mission’

Astronomers have debated for centuries what constitutes a crescent moon sighting. according to a recent study in the journal Scientific Reportswhich explored how artificial intelligence and machine learning could help predict the moon’s visibility.

New technologies make lunar measurements more accurate, but they can also make the process more complex, the study said. For example, does it count as an official observation if a new crescent moon can be seen with an optical aid, but not with the naked eye?

“Deciding on the beginning of Ramadan has always been a challenging mission, and as a result, not all Muslims begin Ramadan in synchrony,” the study authors wrote.

In Islamic countries, national guidance ensures that Muslims adhere to the same Ramadan schedule. In other places, the timing may depend on what religious guidance residents follow. This year, for example, the Fiqh Council of North America elected on Mondaywhile the Council of Shia Muslim Scholars of North America elected on Tuesday.

Other variables

Not only the start date of Ramadan differs from place to place. The exact amount of time people fast from sunrise to sunset depends on what year it is and where they live in relation to the equator.

Since the Hijri calendar is about 11 days shorter than the 365-day Gregorian calendar, the month of Ramadan moves every year in Gregorian terms. That means fasting days in the Northern Hemisphere will become shorter between now and 2031, when Ramadan coincides with the winter solstice. Al Jazeera reports this. In the Southern Hemisphere it will grow incrementally longer over the same period.

In terms of location, latitude matters because it determines the timing of local sunrise and sunset. Muslims who live close to the equator, where the length of a day changes less from season to season, can expect a relatively consistent fasting schedule each year. For those living in extreme northern or southern latitudes, there is much more variety.