diamond geezer

 Thursday, March 20, 2008

Extreme
Early
Easter
(vernal equinox 05:48 GMT, 20/03/07)

It can't have escaped your notice that there's an early Easter this year. Like, very very early. March 23rd is a ridiculously early date for Easter to fall, but that's the way the calendar works out this year. Oh yes, this is most definitely an Extreme Early Easter.

This year's Easter isn't quite record-breakingly early, but it nearly is. There's not been an Easter this early since 1913, which is nearly a century ago and you won't remember that. There won't be an Easter this early again until 2160, which is more than a century and half away and you definitely won't be around for that. And there won't be an earlier Easter than this until 2285, which is so far into the future that we'll probably have drowned the planet by then. Oh yes, this is most definitely an Extreme Early Easter.

Thanks to to some very complicated ecclesiastical rules involving equinoxes and full moons (which I'll go into tomorrow), Easter Day can fall on any Sunday between March 22nd and April 25th. The period between March 28th and April 20th is the most common, and any Easters outside that range are rather less frequent. This year we're right up at the start of the possible range, on March 23rd, because a couple of unlikely events have combined to create a freak rarity. An Extreme Early Easter.

As a movable feast, Easter feels very wrong when it moves too early. It may be nearly three months since we last had a bank holiday, but somehow mid-March is too early to be having a double bank holiday break. School holidays are also all over the place this year because of the early Easter. Some schools are breaking up today and having the next couple of weeks off, whereas others are waiting until mid-April, when Easter "normally" is, and having their break then. Hell, we've not even put the clocks forward yet. And look at the weather, it's more like winter than spring out there. Actually, maybe there's a reason for that. An Extreme Early Equinox.

Today is the first day of spring* - the vernal equinox. The overhead Sun crossed the equator at 05:48 this morning, and we're now entering into the warm half of the year. Yes really, March 20th, not March 21st, is the first day of spring. Spring used to start on March 21st, certainly a century ago it did, but the shifting equinox means that it'll now always be on March 20th. Well, every year from 2008 until 2044 anyway. I explained all this last year, were you not paying attention?
* yes yes yes, I know, northern hemisphere only

It takes the Earth approximately 365 days, 5 hours and 49 minutes to orbit the Sun, so every year the spring equinox shifts almost 6 hours later than the year before. That's approximately 24 hours later every 4 years, which is then cancelled out by the presence of a February 29th a few weeks before the next spring equinox occurs. But this still leaves the calendar 11 minutes short of reality every year, and this tiny difference shifts the spring equinox approximately three-quarters of an hour earlier every 4 years.

So it's not just Easter that's early this year, it's spring too. An equinox before sunrise on March 20th - it's unheard of. In fact the spring equinox hasn't taken place before 6am on March 20th since 1896. Spring hasn't begun this early since the 19th century! But don't get too excited. The phrase "spring hasn't begun this early since the 19th century" has been true every leap year since 1900, and will continue to be true every leap year until 2024. So our premature spring isn't the reason why Easter is early this year. Our early Easter is a result of something that's happening tomorrow. Come back then and I'll tell you more.

• Spring equinox: what it is and why it moves
• Spring equinox: all the times and dates over 4 centuries
• Spring equinox: nice graphs to show how the date and time change

posted 05:48 :

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