How the Date of Pascha is Determined
Most Christians, both Protestant and Roman Catholic, celebrate Easter on March 31 this year. Our Pascha, however, has to wait another five weeks, until May 5th. How come? We’ll try to provide a brief explanation to a very complex problem.
There are three calculations for determining the date of Pascha. The first was established by the First Ecumenical Synod of Nicaea (325) and followed by all Christians, Protestant, Roman Catholic and Orthodox alike:
(1) Pascha falls on the first Sunday after the first full moon after the vernal equinox
(vernal means spring; equinox means equal night, when the sun crosses the equator marking the first day of spring and when daytime and night-time are of equal length). Alas, calculations to establish the dates of the vernal equinox and full moon are not based on actual astronomical data, but on fixed dates, obtained through methods used by the Church for convenience, which, in order to simplify things, we will disregard.
A significant factor in the discrepancy between Western and Eastern Christianity is that
(2) The Orthodox Church calculates the vernal equinox based on the Julian calendar
(established by Julius Caesar in 46 BC), whereas the Western churches calculate the vernal equinox according to the Gregorian calendar (established by Pope Gregory XII in 1582). At the time the Julian calendar trailed behind the Gregorian by 10 days. Currently it trails by 13 days, and by the end of the century by one more day (one day is added every 133 years or about a week per millennium).
The Orthodox Christians also add a condition in the calculation of Easter Sunday the other Christian bodies do not:
(3) Easter Sunday must be after the Jewish Passover.
If our Pascha falls on or before the Jewish Passover, it is postponed to the following Sunday. Since the westerners do not follow this rule it happens that on occasion they celebrate their Easter before the Passover, which does not follow the historical event and is against the tradition of the Church.
This year (2013)
The vernal equinox this year is March 20 (it almost always is on this date, but sometimes it falls on the 19th or the 21st of March), and full moon is March 27, so the first Sunday after that is March 31—the date of Easter for all western Christians.
As we said above, since the Julian calendar is 13 days off, when we add the 13 days to March 20, the vernal equinox is calculated to fall on April 2. The next full moon is April 25. The Orthodox Pascha should fall on the following Sunday, April 28, but it does not, because of other complicated calculations. Thus, this Sunday is disregarded for the following Sunday, May 5. That’s the best I can do. Next year is more straightforward.
Let’s now figure out when our Pascha is next year, 2014.
- Vernal Equinox March 20
- First full moon April 15
- First Sunday April 20 Western Easter
- Jewish Passover April 14
Vernal Equinox is March 20 + 13 = April 2. First full moon is April 15. First Sunday is April 20. Since the Jewish Passover is April 14, the Orthodox Pascha is celebrated on the same day as the Western Easter.
Now you figure out when the Western Easter and our Pascha will be in 2015.
1. Vernal Equinox is March 20, first full moon is April 4, and Jewish Passover is April 4. On which Sunday falls the Western Easter?
April 5, 12, 19, 26 (choose one)
2. On which Sunday falls the Orthodox Pascha?
April 5, 12, 19, 26 (choose one)
Answer to the date of Western Easter and Orthodox Pascha in 2015
March 20 + 13 = April 2. First full moon April 4. First Sunday after that is April 5 on which falls the Western Easter. However, because the Jewish Passover falls on the same day, Pascha is celebrated on the following Sunday, April 12.
Let’s try one more: when is Pascha in 2016?
Vernal Equinox is March 20. First full moon is March 23. First Sunday after that is March 27. Western Easter is on this day. Orthodox Pascha is March 20 + 13 = April 2. But since the Jewish Passover is April 22 the Sunday after that, or May 1, is the Orthodox Pascha.
A few additional facts
This year our Pascha is late. Do you know how late it can be? The latest possible date is May 8, according to the new (Gregorian) calendar. This occurred in 1983. The maximum lag of the Orthodox Pascha is five weeks, which occurs this year. The earliest possible date of Pascha is April 4 (it occurred in 2010, the only time in the entire century).
When do we celebrate Pascha on the same day as the western Christians?
There are those who think that every four years we celebrate Pascha on the same day as the western Christians. This is incorrect. This happens only when the first full moon after the vernal equinox falls after March 28. While next year, 2014, we celebrate Easter on the same day, the next time this will happen is three years later and then after eight years (2025). Then it will be every three years until 2037, after which it will be the following year (that is, we will celebrate on the same day for two consecutive years, something that happened in 1990-1991—if you remember).
Why do we avoid celebrating our Pascha on the same day with the Jewish Passover?
Although we kept the Jewish name Pascha (Pesach, is Hebrew, which means passage), what we celebrate is totally different. The Jews commemorate the passage of the Angel of death, and secondarily the passage through the Red Sea; we Christians celebrate the Resurrection of our Lord and Savior Jesus Christ from death to life. The Church wanted to distance itself from Judaism and established a separate date.