This year, Roman Catholics and other Western Christians are celebrating Easter on April 5, while Orthodox Christians and Ukrainian “Greek” Catholics mark the holiday a week later on April 12. This happens regularly – sometimes the gap stretches to a full month, with Orthodox Easter sometimes falling in May.
Why the difference? While both systems follow the same ancient rule, they use different methods to calculate dates.
The shared rule
In 325 A.D., the Council of Nicaea decided that Easter would be celebrated on the first Sunday following the first full moon that occurred on or after March 21 – the spring equinox.
Catholics, Orthodox Christians, and Protestants all follow this rule.
The calendar problem
The split comes down to calendars. In 1582, Pope Gregory XIII introduced the Gregorian calendar to fix errors in the older Julian calendar. Catholic and Protestant churches adopted it. Many Orthodox churches, however, continued to use the Julian calendar to calculate Easter.
Apply the same rule to two different calendars, and you get two different dates. The Julian calendar has drifted about 13 days behind the Gregorian calendar, which is why Orthodox Christmas, observed on the Julian calendar, falls on Jan. 7 rather than Dec. 25. For Easter, the gap varies from week to week depending on when the full moon occurs.
Some Orthodox churches – including the Greek, Romanian, Bulgarian and Ukrainian – use the Gregorian calendar but still stick with the Julian calendar for Easter calculations. This is why Ukrainian Christians (including Ukrainian Catholics who adhere to the Greek Byzantine rite) will celebrate Easter on April 12 this year. When the Easter rule is applied to the Julian calendar, it yields that date. Sometimes it aligns with the date observed by Western Christians. But often, they don’t.
The extra rule
Orthodox churches have one additional rule: Easter must come after Jewish Passover. Roman Catholics and other Western Christians have no such restriction, which can push the dates further apart.
Why they won’t change
Could everyone celebrate on the same day? They could. But Orthodox churches believe they must preserve the faith as the early Church practiced it. Changing the Easter calculation would mean abandoning rules set by the first church councils – what Orthodox theology views as betraying the early Church.
So, the split continues, rooted in calendars, tradition and competing visions of how to honor the past.