The Easter celebration has ancient roots. The Hebrew Passover is mentioned in the Bible, in Exodus 12:21-24, and is associated with the exodus from Egypt. In Jesus' time, the date was fixed on 14 Nisan, the day of the spring full moon. This date depends on the lunar cycle (13 months or lunations) and not on our current solar calendar of 12 months. In 2024, Easter will be celebrated on March 31.

For Christians: In the 2nd century, the Church chose to celebrate Easter each year on a date close to the Jewish Passover. Christians had already adopted a day of the week as the Lord's feast day: indeed, the eighth day, Christians remember the Lord as eternally living. This day, echoing the first day of creation, became our Sunday, the Lord's day, the feast of the resurrection. Thus, the day of rest shifted in our calendar from the Sabbath to the next day, Sunday.

For the date of the feast itself, linked to the lunar calendar, it was the Council of Nicaea in 325 that wanted to coincide the celebration of Christ's resurrection with the return of spring, on the first Sunday following the full moon after the spring equinox. Many pagan festivals already celebrated this resurrection of nature, but the moon is somewhat unpredictable in its rendezvous with the solar calendar.

Calendar Adjustments The Earth revolves around the sun in 365.2422 days. The count is not exact, which led to the introduction of leap years (every four years) to correct the discrepancy. However, the minor deviation — 365 ¼ instead of 365.2422, or 11 minutes per year — resulted in a difference of ten days between our paper calendar and the solar calendar a thousand years later. In 1582, Pope Gregory XIII decreed to make up for the delay by removing ten days from the calendar: as people went to bed on October 4, the Western world woke up on October 15! The date switched from October 5 to October 15. The Eastern Christians were estranged from Rome for several centuries and did not adopt this reform. Their Easter is still delayed by 11 days today.

And Tomorrow? The variations in date make it difficult to organize the calendar rationally. The date of Easter can vary from March 26 to April 23. The Second Vatican Council expressed a desire for a fixed date, provided it would not cause issues with the Orthodox Church. The discussion is still ongoing.