Calendar and Dates of Easter Sunday
Panos J. AntsaklisAbstract —
The reason for the apparent confusion regarding the dates of Easter is the fact that they are based on both lunar and solar calendars and on rules that are interpreted differently by the Eastern and Western Christian churches. The calculation of the future dates of Easter is and has always been a very important matter because it celebrates the Passion and Resurrection of Jesus Christ. The date of Easter also determines the dates of a number of other religious feasts each year, which are called movable feasts in the church calendar. This article attempts to shed some light into the subject.
In Summary —
According to the Nicaean Ecumenical Council of 325 AD, Easter should be celebrated on the first Sunday after the first full moon after the Spring (Vernal) Equinox.
The Eastern Churches have fixed "Vernal Equinox" to be March 21 of the Julian calendar, which is April 3 in the Gregorian calendar. The Western churches use an astronomical accurate time for the Vernal Equinox, which may be on March 20 or March 21 So, in Eastern churches, Easter falls between April 4 and May 8, while in Western churches Easter falls between March 22 and April 25.
The first full moon after the Vernal Equinox" is not the actual full moon, but it is a calculated, ecclesiastical full moon called the Paschal Full Moon.
The key in calculating the Easter Sunday date each year is the calculation of the date for the Paschal Full Moon (the first ecclesiastical full moon after the Vernal Equinox), which falls on different Gregorian calendar dates for the Eastern and Western churches most of the time. Easter is celebrated on the first Sunday after the Paschal Full Moon.
Eastern churches calculate the Paschal Full Moon using the March 21 Julian calendar Vernal Equinox date (the Paschal Full Moon occurs on or after March 21 of the Julian calendar, that is on or after April 3 in the Gregorian calendar), and a method involving the 19-year moon cycle (Metonic cycle). Easter Sunday in Eastern churches always occurs after the Jewish Passover.
The Western churches use a more astronomically accurate moon cycle (Gregorian method) to calculate the Paschal Full Moon dates. To determine the Paschal Full Moon, the exact times of full moon around March 20 are calculated and compared with the exact time of the Vernal Equinox. If the full moon occurs even a few minutes before the time of the Vernal Equinox that full moon is not the Paschal Full Moon and the next one is taken. This leads to occasional great differences in the Easter dates between churches.
To summarize, the differences in the calculation of Easter Sunday dates between Eastern Orthodox and Western Catholic and Protestant Churches are due to:
(i) the calendars (Julian and Gregorian),
(ii) the time and date taken as the Vernal Equinox, and
(iii) time and date taken for the calculated ecclesiastical full moon around March 20.
Easter Sunday Dates
| Year | Eastern | Western | Passover | Astronomical Full Moon |
| 2007 | 8 April | 8 April | 3 April | 2 April |
| 2008L | 27 April | 23 March | 20 April | 20 April (March 21) |
| 2009 | 19 April | 12 April | 9 April | 9 April |
| 2010 | 4 April | 4 April | 30 March | 28 April (March 30) |
| 2011 | 24 April | 24 April | 19 April | 18 April |
| 2012L | 15 April | 8 April | 7 April | 6 April |
| 2013 | 5 May | 31 March | 26 March | 25 April (March 27) |
| 2014 | 20 April | 20 April | 15 April | 15 April |
| 2015 | 12 April | 5 April | 4 April | 4 April |
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