The Date of the Resurrection Feast
Gregorian and Julian Calendar
The first thing to understand is the difference between the Julian and the Gregorian Calendars. And it's easier to understand when we look at the Nativity Feast... Catholics on the Gregorian Calendar celebrate Christmas on December 25. Orthodox on the Julian Calendar celebrate Christmas on January 7. So how does that work? Why is it like that?
The Julian Calendar is the older calendar. It is a calendar that has the year as being 365.25 days - this means that every four years there is a leap day added to the year (Feb 29).
In 1582, Pope Gregory XIII introduced the Gregorian Calendar as a modification and a replacement of the Julian Calendar. He realized that the Spring Equinox was happening earlier and earlier compared to its expected date of 21 March.
Pause: What does that mean? The Spring Equinox is the day of Spring where day and night are equal length in the day (i.e. 12 hours). The Council of Nicaea in 325 AD discussed the Spring Equinox in their calculations for the Resurrection Feast and determined that it happened on 21 March every year. That's why this was important to Pope Gregory.
So he got some astronomers and scholars together to figure out why it was happening and realized the year is shorter than 365.25 days... it's 365.2425 days long.
So in the Gregorian Calendar, a leap day is still added every four years, UNLESS that year is divisible by 100 (e.g. 1900, 2100, 2200, 2300). But if the year is divisible by 400 (e.g. 1600, 2000, 2400) then the leap day is still added. In my lifetime, we never learned this as kids because I lived in the year 2000 - so it was just a regular leap year. But in the year 2100, there will not be a leap day on Feb 29.
So he did some more calculations to see how many days the calendar was off by since the Council of Nicaea (since his whole framing of the issue was based on the Council of Nicaea's discussion on the date of the Resurrection Feast)
The Difference in Celebration of the Nativity Feast
You can use this information to understand the differences between Christmas for us and Christmas for them...
(Julian length - Gregorian length) * (current year - Nicaea year) = # of days different
(365.25 - 365.2425) * (2023 - 325) =
0.0075 * 1698 = 12.735 days of difference so...
Dec 25 + 13 days = Jan 7
To put this differently, we Orthodox celebrate the Nativity Feast on December 25 according to the Julian Calendar which is January 7 on the Gregorian Calendar.
Coptic Christians celebrate the Nativity Feast on Kiahk 29 which is December 25 of the Julian Calendar, which is January 7 on the Gregorian Calendar.
In the year 2100, the Julian Calendar will have a leap year and the Gregorian Calendar will not. So the number of days of difference will increase by 1 and the Feast of the Nativity will start to be celebrated on January 8... until 2200 when it will go to January 9... until 2300 when it will go to January 10 until 2500 (because there is a leap day in both calendars in 2400).
You can use this calculator to convert between Julian Dates and the Gregorian Calendar: https://stevemorse.org/jcal/julian.html
The Dating of the Resurrection Feast
Now let's talk about the Resurrection Feast.
In the early centuries, Christians used to celebrate the Feast of Pascha (which includes Good Friday and Bright Saturday and the Resurrection) following the Passover. Some areas celebrated according to the Jewish calendar on the 14 of Nisan (Quartodeciman Practice) and some celebrated on the Sunday following the Jewish Passover. You can look up the Quartodeciman Controversy to learn more about this, and it's also mentioned in our Church's Synaxarion.
In the Council of Nicaea in 325 AD, one of the things they wanted to do was unite the celebration of the Resurrection Feast, and to do it without basing it on the Jewish Passover. So they came up with a formula:
- The first Sunday after the first full moon on or after the Spring Equinox.
The Spring Equinox is based on a Solar Calendar. The full moon is obviously based on a lunar calendar. By that calculation, Easter would ALWAYS be AFTER the start of Passover (which was celebrated on the full moon) but NOT BASED on the Passover or the Jewish Calendar. For example, if the Jews were to ever change their calendar and change their Passover to be a month later, Christians would not adjust their calendar to make sure it's "after the Passover" because this wasn't the important part.
Anyway, the Church put together many charts and tables and calculations for matching up these solar and lunar calendars to determine the dates of the Resurrection for Centuries to come. There were some tables in use even prior to Nicaea, such as those by St Demetrius the Vinedresser - 10th Pope of Alexandria, which are still used today.
In those days, the Church and the world followed the Julian Calendar (the calendar that we still follow today in the Orthodox Church).
In the 16th Century, the Catholic Church switched to the Gregorian Calendar (named after their Pope, Pope Gregory) and much of the world slowly started to transition to the Gregorian Calendar because it was more accurate. However, most Orthodox Churches stuck to the Julian Calendar since that was the one used by the Council of Nicaea when they made their determination for the date of Easter, and it's the one used in all of those tables and charts.
Over time, the full moon has shifted by 4-5 days from the tables that were made in those old days. So the date of the full moon in the old tables and charts is referred to as the Ecclesiastical Full Moon, or sometimes the Paschal Full Moon (though this name is used by the Catholics and others who have adjusted their calendars and tables to use the real full moon).
You can read about and see the tables here:
- https://en.wikipedia.org/wiki/Date_of_Easter#Julian_calendar (Julian Calendar which we follow)
- https://en.wikipedia.org/wiki/Date_of_Easter#Gregorian_reform_of_the_computus (Gregorian Calendar which the Catholics follow)
The Date of the Resurrection Feast
You will see that in 2023, the Paschal Full Moon on the Gregorian Calendar is April 5, which is a Thursday. So Easter for those following the Gregorian Calendar will be Sunday April 9. Like Catholic Easter.
You will see that in 2023, the Ecclesiastical Full Moon on the Julian Calendar is March 27. That is Sunday, April 9 in the Gregorian Calendar. So the Sunday following the full moon will be Sunday, April 16 which is the day we will celebrate the Resurrection Feast this year.
In some years, the Catholic and Orthodox Easters are 2-4 weeks apart... this happens when the full moon lands between March 21 (the Gregorian Spring Equinox) and April 2 (Julian Spring Equinox) because it means the Julian Calendar will wait a whole month more for the NEXT full moon.
In many years, the Catholic and Orthodox Easters are just a week apart... this happens because the Ecclesiastical full moon is usually just 4 days or so after the real full moon. So if the real full moon was on Wed, Thu, Fri or Sat, then the Ecclesiastical full moon will fall on the following week and use the following Sunday.
In some years, the Catholic and Orthodox Easters are on the same day... this happens because of the same reason above, but when the full moon was on a Sun, Mon or Tue and the Ecclesiastical full moon was within the same week.
The Jewish Passover
The Jews, on the other hand, celebrate their Passover based on the Lunar Calendar on the 15 of Nisan no matter what day of the week it is. The 15 of Nisan is the day of the real full moon since they are using a strictly lunar calendar. This year, the full moon is April 6 and so they will start to celebrate Passover on the night of April 5.
Conclusion
So it is true that the Orthodox celebration of Pascha (i.e. the Resurrection Feast) will always be AFTER the Jewish Passover. But it is inaccurate to say that the calculation of the date of the Resurrection Feast is BASED on the Jewish Passover.