Why Orthodox and Western Christians Celebrate Easter on Different Days

This year, Roman Catholics and other Western Christians will celebrate Easter on April 5, while Orthodox Christians and Ukrainian Greek Catholics will observe the holiday a week later, on April 12. This phenomenon is not uncommon, as the gap between the celebrations can sometimes extend to an entire month, with Orthodox Easter even falling in May in some years.

So why is there such a difference? While both systems adhere to the same ancient rule, they employ different methods for calculating the dates of the celebration.

In the year 325 AD, the Council of Nicaea determined that Easter would be celebrated on the first Sunday following the first full moon after March 21, the date of the spring equinox. This rule is followed by Catholics, Orthodox Christians, and Protestants alike.

The discrepancy arises from the different calendars in use. In 1582, Pope Gregory XIII introduced the Gregorian calendar to correct the errors of the old Julian calendar. Catholic and Protestant churches adopted it, but many Orthodox churches continued to use the Julian calendar for calculating the date of Easter.

If the same rule is applied to two different calendars, it will yield two different dates. The Julian calendar is approximately 13 days behind the Gregorian calendar, which is why Orthodox Christmas, celebrated according to the Julian calendar, falls on January 7 instead of December 25. Regarding Easter, the difference varies from week to week depending on when the full moon occurs.

Some Orthodox churches, including the Greek, Romanian, Bulgarian, and Ukrainian, utilize the Gregorian calendar but still adhere to the Julian calendar for calculating the date of Easter. This is why Ukrainian Christians, including Ukrainian Catholics who follow the Greek Byzantine rite, will celebrate Easter on April 12 this year. When the Easter rule is applied to the Julian calendar, it results in this specific date. Sometimes, it coincides with the date celebrated by Western Christians, but often it does not.

This situation illustrates the deep cultural and religious differences that exist between Western and Orthodox traditions. It also highlights the significance of calendar systems in determining the holidays and rituals that are important to millions of believers around the world.