Whenever we’re far apart like this, the question always comes up as to why we’re different. Many people erroneously resort to the old, medieval wives’ tale that we always wait to follow the Jewish Passover. Clearly, that doesn’t work, since Jews observed Passover this year on the evening March 25, which is before the March 31 observance of western Christians. The questions still remains then: why are we five weeks later?
The rule for calculating the date of Pascha ever since the First Ecumenical Council (325) is:
the first Sunday
after the first full moon
on or after the vernal equinox (beginning of spring).
Orthodox, Roman Catholic and Protestant Christians all actually follow this rule, but the Orthodox celebrate anywhere from the same day as western Christians to as much as five weeks later (like this year). Why? The quick answer is: because of the Julian Calendar. Read on if you want the details.
1. In the early Church, some Christians always celebrated the third day after Passover, and others celebrated the Sunday after Passover. The First Ecumenical Council decided that the most important thing was for the whole Church to celebrate together. Thus they chose always to celebrate on a Sunday.
2. Then the next question is “which Sunday?,” since not all Jews (then or now) observed Passover/Pascha at the same time. Even though Passover is prescribed in the Bible to be on the 14th of the month of Nisan (a.k.a. Abib), the Jews used a lunar calendar, where the month depended on the Rabbi in each town spotting the new moon. Thus months were variable length, and the first of the month in one town was not necessarily the first of the month in another town or according to another group of Jews. Consequently, the 14th of the month would not be the same from place to place.
3. Furthermore, the Jews in different places were not even always in the same month! The reason is that the lunar calendar had short years: 12 lunar months are less than a solar year. Thus, to keep the months from drifting out of their seasons, an extra month had to be added every several years, but they didn’t add it everywhere the same year. Thus in one place they may have been observing Passover, being the 14th of Nisan on their calendar, while the calendar observed in other places would have been about a month off, somewhere between the 13th-15th of the month of Adar!
This was an impossible situation for the Church’s aim of Orthodox Christians all celebrating together!
4. The First Ecumenical Council decided to abide by the spirit of the Old Testament without depending on the lunar calendar and specifically NOT on when neighboring Jews were celebrating Passover.
5. Since, by definition, the 14th of Nisan would have been at a full moon – half way between one new moon and the next – the Council of 318 Holy Fathers decided the full moon in question would always be the first one after the beginning of spring (the vernal equinox) – no messing with any intercalary months. After that, we just take the next Sunday as Pascha.
6. The Fathers of Nicea assigned the Bishop of Alexandria, where the best astronomical observatories were housed, to announce the date to the entire church yearly. Saint Athanasius sent his famous Festal Letters specifically in fulfillment of this duty.
7. After a while though, people stopped looking at the sun and moon and just used calculations. They could run out tables of calculations for hundreds or thousands of years into the future, and here lies the problem: the calculated positions of the sun (vernal equinox) and moon (being full) deviate from their actual positions.
8. The chief culprit in the divergence between Orthodox and western church calculations – though everybody uses the same formula – is that the vernal equinox is simply always taken to be March 21, though the beginning of spring can actually fall anywhere from the 19th to the 22nd. And the real kicker is that the Orthodox take spring to begin on March 21 according to the Julian Calendar (which presently corresponds to April 3 on the Gregorian Calendar which the civil world uses).
9. So… if the western church calculation (not observation, remember) reckons a full moon between March 21 and April 3, the Orthodox have to wait until the following full moon, which could potentially be just about a full lunar month, and then we observe Pascha the Sunday after that. We could be one, two or five weeks later. That’s what’s happening this year.
10. On those years when there is no full moon between March 21 and April 3, then Orthodox, Protestants and Roman Catholics celebrate together.
Some Orthodox, like us, use the Gregorian Calendar for Christmas and other fixed feasts. Other Orthodox churches use the Julian Calendar for everything; for them, for example, Christmas appears to be celebrated on January 7. All Orthodox, however, use the Julian Calendar when it comes to calculating Pascha and dates that depend on it, like the start of Lent. (The one exception is the Orthodox Church of Finland.) The reason we do this is because, in keeping with the spirit of the First Ecumenical Council, it doesn’t matter nearly as much when we celebrate as long all Orthodox Christians celebrate together.