JAKARTA, Indonesia – Millions of Indonesians owing allegiance to the country’s second-largest Muslim organization began fasting Friday to mark the holy month of Ramadan, a day ahead of most of their compatriots and people in other Asian countries.

The Muhammadiyah group, which has some 30 million followers in the world’s largest Muslim nation, declared the start of Ramadan on Friday. Most of the remaining 190 million Indonesians will start their fast today, which the government has declared as the official start of the holy month.

Malaysia and Bangladesh have also declared Ramadan shall start today, while in India it will be either today or Sunday.

The differing start dates for Ramadan is a routine occurrence. It is due to different ways of calculating when the new moon is sighted to signal the start of Ramadan according to the Islamic lunar calendar.

Ramadan is celebrated by Muslims around the world. It is a period devoted to dawn-to-dusk fasting, prayers and good deeds. It culminates with the three-day holiday of Eid al-Fitr.

Muslims believe God revealed the first verses of their holy book, the Quran, to the Prophet Muhammad during Ramadan. The Muslim lunar calendar moves back through the seasons, so Ramadan starts 11 days earlier each year under the Western calendar.

In Bangladesh, Ramadan is likely to start today. However, a national moon sighting committee headed by the state minister for religious affairs was to sit Friday evening to make an official declaration.

The committee has asked the weather office and members of the public to report to it any sighting of the moon. They examine reports they get from all over the country before making a final announcement.

In India, where about 13 percent of the 1.2 billion people are Muslim, most major Islamic organizations and mosques form committees of religious scholars who determine the start of Ramadan based on the actual sighting of the new moon.

According to Amanullah, the spokesman of New Delhi’s Jama Masjid mosque, one of the country’s leading Sunni Muslim places of worship, Ramadan is most likely to start today.

The moon sighting committee was to meet late Friday to view the moon and officially announce the start of the holy month of fasting, Amanullah said.