YOU'VE PROBABLY heard that old quiz favourite, or variations thereon: "When did Christmas Day fall on Easter Monday?" The Christmas Day involved was a horse, or so it is usually claimed. But by contrast, the question of when Easter falls - and why - never features in quizzes; perhaps because the answer would take all night.
For reasons that remain a mystery outside the world of ecclesiastical astronomy, Easter Sunday ranges over a 35-day cycle. This year it will be on March 23rd, more than a full calendar month earlier than it can be. For the many people affected by the date's vagaries, the whole spring seems out of kilter as a result.
The schools' mid-term break caught parents by surprise - coming, as it appeared to, just after the Christmas holidays. Barely have we recovered from that surprise than we now find the Easter break looming. That this will coincide with St Patrick's Day is also complicating the lives of anyone who works in the tourist industry.
But perhaps the biggest sufferers will be students and teachers with stamina problems. For them, the final term of 2007/08 threatens to be like the uphill finish of the Cheltenham Gold Cup.
So a Galway-based group called the Amicable Society has picked a good year to launch its campaign for a "Fixed Easter". The society comprises former presidents of that city's Chamber of Commerce who take on special projects. And the latest project speaks volumes for their ambition.
In agreeing to publicise the group's call for Easter to be set permanently on the second Sunday of April, the Irishman's Diary is not overly optimistic about a quick breakthrough. After all, the history books suggest that argument about Easter's dating has raged unresolved since the second century AD. But on the plus side, many powerful bodies - ranging from the Vatican to the British House of Commons - have by now agreed on the need for change. . So maybe one last push will do it.
The wide parameters of Easter arise from its links with the Jewish Passover, which - as the Amicable Society explains pithily - "relates to the obsolete Babylonian oscillating lunar calendar, rather than our more stable solar one".
One of the earliest attempts at simplification was the Council of Nicaea in 325, where it was decided that Easter should fall on the first Sunday after the full moon following the vernal equinox. Unfortunately there were already several different astronomical cycles being used to make the calculations, so that in one year, 387AD, Easter Sunday ranged from March 21st in Gaul, to April 18th in Italy, to April 25th in Egypt.
An already confused situation became worse with the Great Schism of 1054 and the later sacking of Constantinople, reverberations from which continue today. Not only do we still have a bewildering range of dates on which the feast occurs. But because Western Christians operate on the Julian calendar, while the Eastern Orthodox church still uses the old Gregorian one, Europe also has two different Easters every year.
The schism explains why, although the Vatican has long favoured fixing a date, it is reluctant to act unilaterally, lest it worsen relations. But even though the Council of World Churches proposed a compromise at a conference in Syria in 1997, no further progress has resulted.
All of which might seem as relevant as arguments about the number of angels you can fit on a pin-head - except that vast numbers of people, many of them devout atheists, have their lives dictated by the calculations at this time of year. It's not just schools, universities, courts, and the tourism sector. Easter marks the turning of the tide in many seasonally affected industries from agriculture to women's fashion. The unpredictability of the dates makes planning very difficult.
This is partly why the British House of Commons passed an Act in 1928 fixing Easter as the first Sunday after the second Saturday in April. The effect would have been to reduce the date's mobility to a much more manageable range: April 9th to 15th. But nothing is ever simple in the Easter debate. And to concerns about secularisation of a religious festival were added the lingering influence of a Scottish meteorologist called Alexander Buchan.
Sixty years before, Buchan had assembled persuasive evidence that at certain regular times of the year the weather was consistently either warmer or colder than the seasonal norm. His six unusually cold periods included April 11th to 14th - bang in the middle of the new streamlined Easter holiday. Nobody pays much attention to Buchan's theory now, but it helped undermine the Easter Act of 1928. Although still on the British statute books, the law remains unimplemented.
I should perhaps point out that, as noted in the Catholic Encyclopedia, the moon according to which Easter is calculated "is not the moon in the heavens, nor even the mean moon: ie a moon travelling with the average motion of the real moon". No. It is the slightly fictionalised "calendar moon" - which at least allows for some simplification.
But I may have confused you enough already. The point is that the growing international consensus on the need for something to be done about Easter now includes both the Amicable Society of Galway and the Irishman's Diary. Surely the pressure for reform has at last become irresistible.