One of our favourite London bloggers, Diamond Geezer, earlier this week picked up on something I’d missed.

If you follow the rule, Easter should be this weekend – the first Sunday after the first full moon following the Spring Equinox. The Equinox was on 20 March and the full moon on 21 March. This would make Easter almost as early as it ever can be.

But it isn’t.

Easter isn’t until 21 April, apparently a full four weeks late, and almost as late as it can be!

WTF is going on?

Well it turns out that the rule isn’t quite what we think it is. Why? Because it was set by the First Council of Nicaea in 325 AD who, amongst other things, set the date of the Equinox in concrete as 21 March when it actually moves around by a day or so. No-one has since redefined it.

This means in some years Easter falls on what appears to be the wrong date, although this is only likely if the full moon and the Equinox are very close together, as they are this year.

I’ll leave it as an exercise for the student to read DG’s post and understand the details.

Another example of the Law of Things Aren’t What They Seem.