Easter date 2019

Elmer Blooker

I've always understood that the date of Easter Sunday is the Sunday that follows the first full moon after the equinox.
This year the equinox was at 2158 on March 20th, the full moon was at 0142 on March 21st so if the first full moon was after the equinox why wasn't Easter Sunday on March 24th?
(source: timeanddate.com)

ps200306

Your definition of the calculation is correct, but the ecclesiastical definitions of both the equinox and the full moon differ from the astronomical ones. The equinox is held to occur on March 21st, regardless of the actual date, and it sets the earliest possible date of Paschal full moon. The date of full moon (of which the Paschal full moon is a particular instance) is an approximation based on the Metonic cycle and can differ from actual full moon by a day or so.

We now whip out the Ecclesiastical Paschal Full Moon Table which we happen to have handy. It is based on a formula derived in 4th century Alexandria and has nineteen rows corresponding to the years of the Metonic cycle. A single column served us fine from the Council of Nicaea (AD 325) until the pesky Gregorian Calendar reform (AD 1582) started dropping three leap days every four centuries. So now we have to nudge the Paschal full moon date by a day every one or two hundred years.



The way we use this is to divide the year by 19, take the first three digits after the decimal point in the answer, and look up the appropriate column. (Don't ask me why they're using decimals instead of remainders). So we get 2019 ÷ 19 = 106.2632. We look up 263 in the 1900-2199 column and see that the Paschal full moon is on April 18th. Easter is the following Sunday. Simples. :pac:

coylemj

Elmer Blooker wrote: »

I've always understood that the date of Easter Sunday is the Sunday that follows the first full moon after the equinox.
This year the equinox was at 2158 on March 20th......

As poster ps200306 has pointed out above, the equinox is fixed at March 21st for the purpose of the calculation of the date of Easter.

When Julius Caesar instituted the 365/365/365/366 calendar cycle in 45 B.C., it assumed the solar year lasted exactly 365.25 days but in fact it's very slightly less than this and the effect of this error was that the Vernal Equinox started to drift back in time from it's original date of March 25th. By the time of the First Council of Nicea in 325 A.D., the equinox had moved to March 21st and when that council set about defining a method to calculate the date of Easter, they fixed the date of the equinox at March 21st.

The equinox continued to drift back in time so when Pope Gregory XIII modified the calendar in 1582, 10 days were dropped in October of that year in order to restore the equinox to March 21st.