How Easter is calculated has always puzzled me, because there doesn't seem to be any one rule which is always followed.

Anyone who thinks it's a simple matter should read this:

The usual statement, that Easter Day is the first Sunday after the full moon that occurs next after the vernal equinox, is not a precise statement of the actual ecclesiastical rules. The full moon involved is not the astronomical Full Moon but an ecclesiastical moon (determined from tables) that keeps, more or less, in step with the astronomical Moon.

The ecclesiastical rules are:

* Easter falls on the first Sunday following the first ecclesiastical full moon that occurs on or after the day of the vernal equinox;
* this particular ecclesiastical full moon is the 14th day of a tabular lunation (new moon); and
* the vernal equinox is fixed as March 21.

resulting in that Easter can never occur before March 22 or later than April 25. The Gregorian dates for the ecclesiastical full moon come from the Gregorian tables. Therefore, the civil date of Easter depends upon which tables - Gregorian or pre-Gregorian - are used. The western (Roman Catholic and Protestant) Christian churches use the Gregorian tables; many eastern (Orthodox) Christian churches use the older tables based on the Julian Calendar.

The formula for Easter--"The first Sunday after the first full moon on or after the vernal equinox"--is identical for both Western and Orthodox Easters, but the churches base the dates on different calendars: Western churches use the Gregorian calendar, the standard calendar for much of the world, and Orthodox churches use the older, Julian calendar.

That much is straightforward. But actually calculating these dates involves a bewildering array of ecclesiastical moons and paschal full moons, the astronomical equinox, and the fixed equinox-- and that's in addition to the two different calendar systems.

When is A Full Moon Full?

The two churches vary on the definition of the vernal equinox and the full moon. The Eastern Church sets the date of Easter according to the actual, astronomical full moon and the actual equinox as observed along the meridian of Jerusalem, site of the Crucifixion and Resurrection.

The Eastern Orthodox Church also applies the formula so that Easter always falls after Passover, since the Crucifixion and Resurrection of Christ took place after he entered Jerusalem to celebrate Passover. In the Western Church, Easter sometimes precedes Passover by weeks.

How the Easter Bunny fits in with all this I am not sure

Orthodox Christianity does not seem partial to the bunny tradition:

But that last site has a sense of humor about the history:

The bunny, the use of eggs that time of year (though there is a Jewish antecedent here as well) and even the name 'Easter' (Eostre, a goddess) are all from Germanic pagan fertility/springtime customs. 'Pascha' is a better name but of course in English I use 'Easter' as it is commonly understood.

It's still weird to see images of bunnies everywhere, cute as they are, when you know what Pascha really is.

The Easter Bunny is not a modern invention. The symbol originated with the pagan festival of Eastre. The goddess, Eastre, was worshipped by the Anglo-Saxons through her earthly symbol, the rabbit.

The Germans brought the symbol of the Easter rabbit to America. It was widely ignored by other Christians until shortly after the Civil War. In fact, Easter itself was not widely celebrated in America until after that time.

Obviously, this means we won't have many more Easters! Instead of the Easter Bunny, and Easter egg hunts, children should be treated to Eco-Frights about Global Warming. (Especially because this year, the poor Easter bunny is a victim of coldening.)

Traditional or not, enjoy your Easter while you can!

UPDATE: Today's Easter coldening seems to have started in the South by coldening advocate Al Gore. First, Gore flew to Nashville. This triggered a precipitous drop in temperatures over the Easter weekend to the lowest in 85 years. Gore's emboldened coldening front then moved North, where it struck Richmond with an Easter snow. Glenn Reynolds was initially skeptical over Gore's coldening powers could be this great, but the evidence is accumulating. The coldening has spread to Cleveland.

Here in the Philadelphia area, we're far enough away from Al Gore that we're just catching the tail end. I've only seen a few Easter snowflakes so far.