Why Easter hops around the calendar

Ruth Griffiths

Businesses depends on it, school calendars must accommodate it and vacation plans revolve around it, but the actual date for Easter hops around like a bunny.

Easter is the most important Christian feast but the proper date of its celebration has been the subject of controversy for centuries. In 325, the Council of Nicaea established that Easter would be held on the first Sunday after the first full moon occurring on or after the spring equinox.

In 1583, the Catholic Church began using March 21 under the Gregorian calendar to calculate the date of Easter, while the Eastern Churches have continued to use March 21 under the Julian calendar.

The earliest and latest dates for “Western” Easter are  March 22 and April 25. However, in the Orthodox/Eastern Churches, while those dates are the same, they are reckoned using the Julian calendar; therefore, on the Gregorian calendar those dates are April 4 and May 8. To further confuse the issue, occasionally the “Eastern” Easter falls on same date as the Western Easter. That will happen in 2025 when Easter is on April 20.

According to the Bible, Jesus held the Last Supper with his disciples on the night of the Jewish festival of Passover, died the next day (Good Friday) and rose again on the third day (the following Sunday). Easter celebrates the resurrection of Jesus on that Sunday.

The beginning of Passover is determined by the first full moon after the vernal equinox, which can occur on any day of the week. To ensure that Easter occurs on a Sunday, the Council of Nicaea therefore ruled in 325 that Easter would be celebrated on the Sunday after the first full moon on or after the vernal equinox. But there’s a twist: if the full moon falls on a Sunday, then Passover begins on a Sunday, so Easter is then delayed by a week to ensure that it still occurs after Passover.

To confuse matters further, the council fixed the date of the vernal equinox at March 21, the date on which it occurred in 325 (though it now occurs on March 20), and introduced a set of tables to define when the full moon occurs that do not quite align with the actual astronomical full moon (which means that, in practice, Easter can actually occur before Passover).

We celebrate Christmas on Dec. 25, why couldn’t Easter be celebrated on a fixed date? Several churches, including the Catholic church, say they are open to the idea of setting the date of Easter in this way, but until there is widespread agreement, its date will continue to jump around within a five-week window. Hoppy Easter!