There had been confusion about whether Eid al-Fitr would begin Tuesday or Wednesday, due to differences around the world in the sighting of the moon. Muslims base the Eid day at the end of Ramadan on the sighting of the new moon.

But in Saudi Arabia and the UAE, a sliver of the new moon was sighted after dusk on Monday, the Associated Press says.

Saudi Arabia announced that Ramadan has ended, and the three-day Eid al-Fitr holiday will begin Tuesday. Many countries follow Saudi Arabia's lead as the country is home to the holy city of Mecca, the Washington Post explains.

Sighting the new moon to determine the first day of Eid al-Fitr is always a tough task, an astronomer who is a member of the United Arab Emirates' Moon Sighting Committee told the Gulf News.

"During the last two days of the month, the moon will be beyond the horizon after sunset, so it is difficult to observe it," Sakher Abdullah Al Saif says.

Festivities are to begin soon after the early morning prayers on Tuesday. The first day of Eid is traditionally spent visiting relatives, especially elders in the family, and eating specially prepared food, the Gulf News says.

The Wall Street Journal writes that while in the past the geographical differences in sighting the new moon wouldn't have mattered much, today with increasing global connectivity, more Islamic leaders are keen to have 1.2 billion Muslims celebrating together around the world.