Bulletin Q&A Article; Published 2-11-24:
Why to the Orthodox Churches celebrate Easter on a different date than Catholics?
Ash Wednesday is this week, and of course the date for Ash Wednesday is back-calculated from the date of Easter which is the key for determining other moveable feasts. So we can start our discussion by explaining how the date of Easter is determined. Easter was set by the Council of Nicea in 325 AD as the first Sunday after the first full moon after March 21st, the approximate date of the vernal equinox. This year the first full moon after March 21st is on Monday March 25th. Therefore, Easter is the following Sunday, March 31st. Easter can be no earlier than March 22nd and no later than April 25th.
The Orthodox Churches use the same formula as the Catholic Church, however they use the Julian calendar for determining their religious feasts instead of the more widely used Gregorian calendar. (For more on this, refer to my bulletin article from last month regarding celebrating Christmas on January 7th. You can find it on my blog at: https://orthoscopy.net/index.php/2024/02/02/christmas-on-january-7th/) In short, the two calendars are out of sync by 13 days. March 21st on the Julian calendar corresponds to April 3rd on our Gregorian calendar and no longer has any association with the vernal equinox. This year, the first full moon after April 3rd is on Tuesday, April 23rd so one would think that the Orthodox Churches would celebrate Easter on Sunday, April 28th. But I looked it up and found that instead they will celebrate on May 5th. This left me greatly puzzled and required further investigation.
It turns out that neither the Catholic Church nor the Orthodox Churches use the actual astronomical day on which a full moon occurs. Catholics use an ecclesiastical calendar with an 84-year cycle to determine the full moon dates. It is fairly accurate and varies from astronomical full moon dates by no more than a day. The Orthodox, however, use a 19-year cycle developed in the 5th century BC by a pagan Athenian astronomer named Meton. The “Metonic” cycle is much less accurate and usually indicates the date of the full moon 4-5 days after the true date. Because of this, a full moon that actually occurs on a Tuesday can show up on their ecclesiastical calendar as being on the following Sunday. And this causes a delay of one week in celebrating Easter. This is why Orthodox Easter is often one week later than Catholic Easter.
Sometimes the celebrations of Easter by the two Churches coincide. It happened in 2017 and will happen again next year in 2025. Next year there will be a full moon on Sunday, April 13th. We will celebrate Easter on April 20th. Even with the error in their calendar shifting their full moon date to Friday, April 18th, the Orthodox will celebrate on April 20th as well.
It is interesting to note that Catholics in Greece celebrate Easter on the Orthodox date out of concern for the local community. In 2016, the Holy Synod of the Catholic Hierarchy of Greece put out a statement pointing out the errors in how the date of Easter is calculated by the Orthodox. (https://www.johnsanidopoulos.com/2021/04/how-is-date-of-easter-determined.html ) They conclude by writing: “The date of the celebration of Easter is not a doctrine of faith. It is the result of mathematical calculations that have to do with the movement of the Moon around the Earth and the Earth around the Sun. That is why the Catholic Church in Greece, both for practical reasons, to facilitate its faithful (mixed families, public holidays, etc.), and for ecumenical reasons, for more than forty years and knowing the miscalculations, celebrates Easter with the Orthodox Church.”
Deacon Joe