Was it to ratify an astronomical miscalculation or eschew a bad omen, asks Jailan Halawi, that the date of Eid Al-Adha was changed at the last minute? Today Muslims all over the world are celebrating Eid Al- Adha , the grand feast of sacrifice that is also the culmination of the annual pilgrimage to Mecca. Major Muslim holidays are always anticipated with uncertainty, since the lunar calendar of 354 days is rather more variable than its universally accepted solar counterpart, resulting in dates shifting from year to year. Because the start of a new month is often based on direct observation of the moon, the holy month of Ramadan, for example, may begin on different days in different parts of the world. Not so with Dhul-Hijja, however, the last and holiest month in the Muslim calendar, the ninth day of which marks the pilgrims' most central rite -- the climb up Mount Arafa -- thereby concluding the Hajj, fifth pillar of the Muslim faith. The date of Eid Al- Adha is therefore determined in advance by Saudi Arabia's Supreme Judicial Court and accepted unquestioningly by everyone in the Muslim world. Earlier this year Saudi Arabia had announced that, according to the court's calculations, the first day of the four- day feast would coincide with Friday 21 January; the climb up Arafa would therefore take place on Thursday 20 January. Yet unexpectedly, on Friday 14 January, the Saudi authorities announced a change of day: the Eid would begin on Thursday 20 January, a day earlier than previously announced, and the change was immediately conceded by Egypt's Dar Al-Ifta' (the body officially in charge of issuing fatawa or religious edicts), which made a statement the next day (Saturday) reiterating a principle agreed upon during the Jedda Conference: Muslims are required to abide by Saudi observations of the crescent marking the start of Dhul-Hijja, since the dates are linked with the rites of Hajj and therefore have to be unified. The office of the prime minister followed suit, shifting back the start of the Eid holiday to Wednesday, with five days off for civil servants and four for employees of banks. The abrupt change left Egyptian railway stations in a state of chaos, with thousands of holidaymakers having planned vacations and booked tickets based on the original announcement. Despite the best efforts of railway officials, Upper Egyptians resident in Cairo especially are likely to spend the first day of the Eid away from family. The chaos beset domestic flights and hotel bookings as well, with resorts in the Red Sea and Aswan expecting pandemonium. It seems only fair to ask what possessed the Saudis to change their mind about the crescent at the last minute? On the popular level, the change has generated all manner of theorising, much of which is meant only in jest. Well known for their sense of humour, the Egyptians' immediate reaction was to circulate jokes through mobile phone messages: "First it was Friday, now it's Thursday; let's hope good things will come earlier this year"; "They said the feast was on Friday and now they say it's Thursday, so I thought I'd send my season's greetings quickly before they cancel it altogether"... The jocularity soon gave way to "the bad omen theory". According to 33-year-old engineer Yassin Badri, for one proponent, there is a belief among Saudis that if the feast of sacrifice occurred on a Friday, the king would die before too long: the belief spread in the early 1980s, he said, following the death of the Saudi king in the wake of Eid Al-Adha, which had occurred on a Friday. Accountant Mona Essam, who lived in Riyadh for 16 years, thought the theory does not hold water. She explained the change, rather, by the fact that, while astronomical calculations are made, the Saudi authorities trust the verdict of Bedouins who observe the moon traditionally without the aid of telescopes: where the findings contradict each other, the Bedouin verdict is accepted. This raises the question of whether such a method should really take precedence over the more accurate means provided by modern science. The question has in fact been at the centre of a heated debate for many years: religious scholars insist on the traditional method, which is in line with procedures observed during Prophet Mohamed's lifetime; astronomers point out that modern methodology is infinitely more accurate. According to Astronomical Research Centre Professor Ahmed Shaltoot, in Egypt astronomical calculations are believed to be complementary to the traditional method, but in the end, he said, it is the Saudis' verdict that must be accepted, "for they are the ones who have Mount Arafa" -- an argument one cannot, in the end, seriously dispute. The feast of sacrifice marks the test of faith to which Prophet Ibrahim was subjected, when God ordered him to offer his son Ismail in sacrifice -- a command he was in the process of carrying out when God intervened, at the last minute, allowing him to slaughter a ram in Ismail's stead. Every year Prophet Mohamed sacrificed a ram to commemorate the occasion, establishing the tradition as an annual rite for all Muslims who can afford it. This test of faith is central to Islam: submission to God's will is the very mark of a true Muslim, and how better to demonstrate the extent to which one is willing to submit than to show willingness to part with the thing you love and value the most. For the time being, sacrifice aside, it is with their holidays that many Egyptian Muslims will be forced to part.