Tuesday, March 25, 2008

Easter time

Originally uploaded by foreverdigital
A friend noticed that we often say that Easter is early (as it was this year) or late... but we never say, "Hey, Easter is on time this year!" I thought therefore that it would be useful to define a set of dates where Easter could officially be declared to be on time. However, this has turned out to be slightly trickier than anticipated. (It becomes even murkier when you take the Eastern Orthodox Church's calculations for Easter into account... so this post will only consider the dates chosen by the Western churches.)

My first thought was to take the earliest possible date for Easter (21 March) and the latest possible date (24 April) and simply divide the time between into three sections: early, on time and late. That gives eleven days, from 2 April to 12 April inclusive, where Easter would be declared to be on time. The problem is, some dates for Easter are more likely than others and there's not an even distribution. For example, the most common date for Easter is 19 April which falls outside my "on time" slot - that may be OK, but it feels wrong.

What I need therefore is someone with the time and the mathematical inclination to analyse all the possible dates and come up with an 11 day slot which will result in the number of years where Easter is late being roughly the same as the number of times it is early. Since the pattern of dates repeats after 5,700,000 years, it shouldn't be too hard to work out. :-) Anyone up for the challenge?

Once a time slot has been chosen, we can start a Campaign for On Time Easters (COTE).

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Chris said...

This is a great take on Easter - gave me a laugh among the swirling snow. Easter week? I'm all for having it when the weather is suitable - much harder to calculate!

Alan Y said...

made me laugh - especially now that we have a spring break.
Can you let us know how Easter is calculated? Someone once told me it was the second Sunday after the first daffodils appeared but I'm not sure I still believe them. Is it the second weekend after the 3rd full moon of the year?

Duncan__ said...

"Can you let us know how Easter is calculated?"

Jeez, you'd think they'd have look-up tables for this sort of thing! ;-)

Steve said...

David, you have far too much time on your hands. An amusing article - keep up the good work.

David said...

Hello Chris & Alan

I'm happy if I've made you happy. :-)

Hello (again) Alan

Nothing to do with daffodils as far as I know. Based on the phases of the moon... except it would be to easy to base it on the real phases of the moon. Instead, it's based on a notional ecclesiastical moon!

Hello Duncan

No... looking stuff up is too easy.

Hello Steve

Too much time? Moi?

Anonymous said...

if only the s/clyde email system was decent enough to let through non macro'd excel sheets that calculate the timeliness of easter

David said...

Assuming "Anonymous" is Barry... I did get your spreadsheet and I apologise for not acknowledging it. I'm planning a follow up post where your work will be featured. :-) I'll email you before 5 post.