The Epact Computation: An Alexandrian Achievement for All Christian World

One of the many significant original achievements of Abba Dēmētrios I (12^th Patri­arch of the See of Saint Mark in Alexandria: 189-231 AD) was the method he devised for calculating the Date of Easter so that it would always fol­low the Passover, just like the Rest Easter Sunday, according to the historical biblical events. This method is known as the Epact, and to this day it is followed by all Eastern Or­tho­dox Churches in determining their Ea­ster date very many years in advance. It involved making a correlation between the lu­nar (Se­mi­tic) year and the solar (Egyptian) year. This was necessary because the lunar year is shorter than the solar year by ele­ven days, and a fixed date in it can fall in any season as the years go by, and would de­viate Easter from the Passover. When Abba Dēmētrios per­formed the Epact Computation, he convoked the Holy Synod, and explained it to its Members. They approved it and decided to abide by it. Many years la­ter, in 325 AD, when the 1^st Œcumenical Council of Nikaia met, this computation was submitted to it, and was again un­animously accepted. It continued to be fol­lowed by all Christian Chur­ches until 1582 AD, when the ca­len­dar was changed by Pope Gregorius XIII of Rome. Sin­ce then the Western Churches depar­ted from it, and now they observe Easter on the first Sunday after the Full Moon following the Vernal Equinox, regardless of the Pass­over. All the Eastern Churches, however, still adhere to this old computation (Computus), hence the di­ver­gen­ce between the Eastern and Western Churches on the Date of Easter celebration persists.