When Easter is celebrated
A common way to explain when Easter takes place is by saying that it’s the first Sunday after the first full moon of spring. However, one should also take note of the following facts:
- The beginning of spring is taken ecclesiastically, and as such it is fixed permanently as 21 March (decided in 325 AD at the Council of Nicaea). If we were to judge it by the beginning of the astronomically determined spring, it could be up to two days earlier, because while the astronomical spring often starts on the 21st, it just as often falls on the 20th of March, and sometimes even appears on the 19th.
- When the full moon is calculated using “cyclic calculations” it can differ from the actual astronomical full moon by up to two days.
For this reason, exact astronomical phenomena is not used when determining the calendar date of Easter Sunday!
A more complete definition could be explained as follows:
- Easter Sunday falls on the first Sunday after the Paschal (ecclesiastical full moon), which being fixed as 21 March, makes Easter Sunday capable of occurring as early as 22 March and no later than 25 April.
The difference between astronomical and ecclesiastical was most recently noticeable in 2019, when the first day of spring was 20 March and the next day (Thursday, March 21) was an astronomical full moon. Easter Sunday could have taken place on Sunday, the 24th of March, but because the calculated Paschal full moon was not until Thursday, the 18th of April 18, Easter Sunday didn’t occur until 21 April! The difference in the dates was 28 days, making it part of the “Easter paradox” phenomena. The next Easter paradox will not be seen again until 2038.