Straining at Lunar Gnats

This week's Nature has a news story concerning the Muslim lunar calendar. Apparently a group of American Islamic scholars has agreed on a unified lunar calendar.

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. ...

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. [italics added]

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.

Sheesh.

Speaking of the moon, last weekend NASA crashed a probe into it resulting in a flash of light that was visible from earth (though not with the naked eye, I think). Nature used the occasion to put together a special feature about the Moon. It is freely available; I recommend this slideshow.