The Muslim community in the United States has taken a small but significant step towards resolving one of the oldest disputes between Islam and science — the creation of a unified lunar calendar.

Islam, in common with Judaism, uses lunar dates worked out in accordance with the phases of the Moon. But despite major advances in lunar astronomy over the past few centuries, Muslims have never agreed a single lunar calendar. This may finally be about to change. At a meeting last month, the Fiqh Council of North America, a body of American Islamic religious scholars, agreed that religious festivals in the United States such as Eid, the end of the fasting month of Ramadan, will now be fixed according to a predetermined calendar.

In a statement on 28 August, Muzammil Siddiqi, chairman of the Fiqh Council, said: “Muslims will be able to plan their activities in advance, take time off from work or school. It will reduce a lot of chaos, hardship and confusion.”

The timing of Islamic festivals in the United States will no longer rely on direct sightings of the Moon. Credit: D. SANSONI/IMPACT PHOTOS

The move was welcomed in Britain by Zafar Iqbal who chairs the Islamic Calendar Committee of the Muslim Council of Britain, a coalition of some 400 mosques and community groups. Iqbal believes that the US decision will strengthen calls for Britain's estimated 1.6 million Muslims to adopt a unified calendar. “This is a very courageous decision,” he says.

The US decision has its critics among both scientists and theologians, including members of the Fiqh Council itself. One member says he doesn't think the move will have universal appeal — especially among those who believe that it is a religious requirement for the beginning of each lunar month to be confirmed by a naked-eye sighting of the new Moon.

This need to see the new Moon dates from the time of the Prophet Mohammed in the seventh century. And there is a reluctance to switch from what people believe Mohammed required, regardless of whether a scientific approach might be more convenient — in fact doing so is seen by many Islamic scholars as coming close to committing a sin.

Seeing the Moon with the naked eye is a means to an end; it should not be seen as an end in itself.

Usama Hasan, a lecturer in computer science at Middlesex University, UK, is an Islamic scholar and has collaborated with the Royal Observatory in London. He says that the council should have used a more accurate method to compile the calendar. The council opted for a method based on computing the position of the Moon relative to Earth and the Sun. But Hasan says that the technology now exists to predict whether the Moon will be visible in a certain place at a certain time, which comes closer to the requirements of Islamic tradition. “Seeing the Moon with the naked eye is a means to an end; it should not be seen as an end in itself,” he says.

But the naked eye remains the method of choice throughout the Islamic world, and is one of the main reasons a unified calendar has so far proved elusive. According to this tradition, a new lunar month begins the morning after a sighting of the thin crescent Moon — some 24 hours after the birth of a new Moon.

That's difficult for countries in the Northern Hemisphere, because thick clouds often hide the crescent Moon. And in countries at higher latitudes, such as in Scandinavia, the crescent is invisible to the naked eye. When this happens, mosques in northern Europe and North America tend to follow decisions in other countries. Saudi Arabia and Pakistan are favourites, but even they often celebrate Islamic festivals on different days.

Hasan is confident that the US decision will prompt a rethink in Saudi Arabia, where Moon-sighting causes frequent controversy. Saudi Arabia does have an Islamic calendar based on lunar tables, known as the Umm al-Qura calendar. This was developed by the King Abdulaziz City for Science and Technology, the country's science ministry, and is used for all non-religious purposes. But human sightings are still used to determine dates for religious festivals. Moreover, anyone can claim to have seen the Moon — the authorities are duty-bound to listen, and sometimes accept news of a sighting even if this does not agree with the dates in the lunar calendar.

This happened last year, when the Saudi government decided, with just ten days to go, to revise the date for the annual Hajj pilgrimage because of a claimed Moon sighting — even though astronomical calculations showed such a sighting to be impossible. The sudden change led to chaos in the organization of the three-day event, which attracts 2 million people from more than 150 countries.

Siddiqi, too, is hopeful that the use of lunar calendars will catch on, if only to rule out erroneous sightings.