Did you know that Easter will be celebrated on April 14th this year? It will be by those who observe Eastern Orthodox Easter, but Western Christians will celebrate it on March 23rd. Why the difference? Most Orthodox congregations observe Easter according to the Julian calendar; all others observe it according to the Gregorian calendar.
Many of us have learned that Easter is the first Sunday after the full moon which occurs upon or after the vernal equinox. This was true when it was established by the Council of Nicea in 325; however, calendars and calculations have changed since then and so this is not technically correct.
First of all, it’s not the astronomical full moon that is used to calculate Easter, but rather, the fourteenth day of a lunar month, calculated by an ancient ecclesiastical computation, which gives us the Paschal Full Moon (which can vary as much as two days from the astronomical full moon).
Secondly, since 326 A.D., the Easter Sunday date for any given year has not been determined by the March Equinox date (which can be either the 20th or the 21st), but by March 20th only.
Each year it is the intention of Christian churches to celebrate Christ’s resurrection on a Sunday that would correlate with the exact day of the astronomical full moon on which his resurrection was said to have taken place; however, solar and lunar months don’t match, hence the development of a method of calculation and its various revisions which have taken it from its basis in the old Jewish calendar to the Julian, and then the Gregorian calendars.
Most Christian scholars have placed the Last Supper on Passover (the 14th day of Nisan), the crucifixion on the 15th, and the resurrection three days later on the 17th. Three days in the grave – from the 15th to the 17th appears to be a discrepancy until we take into consideration that WE count the days from midnight to midnight, but ancients considered the new day as beginning at sundown the day before; hence the day of what we consider to be the 15th was considered by them to be a continuation of the 14th.
Is your head spinning yet? There are ever so many more technicalities and intricacies to the method of calculating Easter, and those of you who enjoy debating how many angels can dance on the head of a pin may enjoy pursuing more information about the Golden Number, the Metanomic Lunar Cycle, and the Epact on the Catholic Encyclopedia website.
And this site not only gives a great explanation of the calculation of Easter, but also provides information about Jewish, Islamic, Chinese and Indian calendars that are in use (and some others that are not)
So, how do we answer the question “how is Easter calculated?” As you can see, a technically correct answer could be incredibly complex; how about we all continue to say “it’s after the first full moon which occurs on or after the vernal equinox” and let’s just leave it at that!