Why does the date of Pascha differ from Western Easter so much? (May ’02)
Determining the date of Pascha has been an issue for the Church since its earliest days. Christian converts from Judaism who were familiar with the date of Passover would often celebrate Pascha on the same date of Passover. That date was the 14th day of the Hebrew month Nisan. In Asia Minor, the churches celebrated Pascha on the 14th of Nisan whether it fell on Sunday or a weekday. Many other churches celebrated Pascha on the Sunday that followed the 14th of Nisan.
Eventually, somewhere towards the end of the Second Century, the churches of Asia Minor agreed to celebrate Pascha with the other churches on the Sunday after the 14th of Nisan. So the date for the observance of Pascha was based on the Jewish Passover. The Jews celebrated the Passover on the first full moon following the vernal equinox.
With the dispersion of the Jews after the Destruction of the Temple in 70 A.D., the date of calculating the beginning of the month of Nisan and the full moon of Passover varied due to the use of local pagan calendars. For this reason, many Christians stopped utilizing the Jewish Passover to determine the date for Pascha.
“Paschal cycles” were then devised as a way to determine the date of Pascha. Two cycles developed. In the East, they adopted a 19-year-cycle, while in the West they used a less accurate 84-year-cycle. Due to the usage of two different “Paschal cycles,” the Eastern and Western Churches had differences in when they would observe Pascha. Also added to the problem was the observance of the vernal equinox: the West used March 18th and the East March 21st.
Finally, in 325 A.D. at the First Ecumenical Council in Nicea, the Church officially addressed the problem and stated how to determine the date of Pascha. The following rules are to be applied:
1) Pascha must be celebrated after the vernal equinox;
2) it must be celebrated after the first full moon following the vernal equinox;
3) it must be celebrated on the first Sunday following the full moon after the vernal equinox;
4) and it must also follow the seven day period of the Passover.
As the main source for this answer, I relied on an explanation offered by Dr. Lewis Patsavos, Professor of Canon Law at Holy Cross Greek Orthodox School of Theology that appeared in The Orthodox Church: 455 Questions and Answers by Fr. Stanley Harakas.
