Romain Rouillard / Photo credit: MASSIMO VALICCHIA / NURPHOTO / NURPHOTO VIA AFP 7:00 a.m., March 28, 2024

This year, Easter will be celebrated on April 1, ten days earlier than last year. Unlike Christmas, the most important holiday in Christianity does not have a fixed date and generally runs from March 22 to April 25. The result of a calculation method based on astronomy. Europe 1 takes stock.

Next Sunday, March 31, Catholics around the world will celebrate Easter. The date chosen this year for the most important festival in Christianity, which commemorates the resurrection of Christ, has been brought forward by ten days compared to last year. In 2022, Easter was even celebrated on... April 17. So why was this religious holiday set so early this year?

In reality, Easter can take place as early as March 22 and extend until April 25. Unlike Christmas, this celebration does not have a fixed date and can therefore be held between these two ends. A particularity which has its origin in the very definition of Easter, developed on the occasion of the Council of Nicaea, in present-day Turkey, in 325. 

The story of a gap 

“It was the beginning of Christianity and there were different rules. During this council, it was therefore felt that Christian unity wanted all Christians to celebrate Easter on the same date,” explains Denis Savoie, astronomer and historian. Sciences. Gathered around the Emperor Constantine, the bishops of the Roman Empire agreed to retain the following definition: “Easter is the Sunday following the fourteenth day of the Moon which reaches this age on March 21 or immediately thereafter”. 

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In other words, Easter will systematically fall after the full Moon which follows the spring equinox, therefore set for March 21. “On the other hand, the full Moon can fall on March 22, 23 or 24, until April 25. It is this mobility of the full Moon that explains why Easter oscillates between these two dates,” explains Denis Savoie . 

At the time, another problem quickly arose: that of the Julian calendar, in force since Julius Caesar, in 45 BC. A calendar, developed with the help of an astronomer, which had a delay of approximately 11 minutes with the solar year. This slight dissonance between the calendar year and the astronomical year was only discovered during the Renaissance, but posed more and more difficulties in fixing the date of Easter. "We can say that 11 minutes is not a lot, but after a while it adds up. After the 4th century, we saw that the spring equinox began to fall on March 20, then the 19, 18, 17 etc. Easter is starting to wander around everywhere,” says Denis Savoie. 

The reform of Gregory XIII 

In the 16th century, this equinox even fell on March 11 and pushed Christianity to react. The Council of Trent then summoned the papacy to find a solution and Pope Gregory XIII brought together a commission of astronomers to ratify the creation of the Gregorian calendar which would replace the Julian calendar in force for 14 centuries. The reform was abrupt to say the least since ten days were thus purely and simply eliminated in this year 1582. The French moved suddenly from Thursday, December 9 to Friday, December 20. Three leap years out of 100 years are also eliminated. 

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However, this new schedule does not apply to everyone. In conflict with Rome at the time, the Orthodox decided to keep the Julian calendar. “Today we have a gap of 13 days between the two calendars. Julian Easter has the same definition as Gregorian Easter, but as you have this difference of 13 days, the Easter celebration is also shifted.” This is why the Orthodox regularly celebrate this holiday during the month of May. Rarely, in 2014 and 2017, Catholic Easter and Orthodox Easter were celebrated on the same day.