This year’s 1,700th anniversary of the Council of Nicaea is suitably marked by both the Catholic and Orthodox Easter falling on the same date, which is not the norm. It was at Nicaea that the date of Easter was set; it was one of the most important items on the conciliar agenda.

The anniversary and the joint celebration this year have fostered hopes that a permanent joint celebration of Easter might be possible. That remains unlikely, however, given that relations within the Orthodox world do not permit such a momentous decision to be made. 

Nicaea and Easter

While Nicaea is remembered for the doctrinal defense of the divinity of Christ against the heresy of Arianism — which taught that Christ was not fully divine — the date of Easter was a pressing issue. 

By 325, Constantine had legalized Christianity and strongly supported it as a unifying force in the Roman Empire. One reason for convening the council was to promote imperial unity by resolving theological disputes. Divisions within the increasingly influential religion could destabilize the empire and potentially threaten the emperor’s authority. 

The same was true for religious celebrations, which touched the common life of the people more directly than theological questions. If the entirety of the now-Christian empire could celebrate its most important feast at the same time, it would underscore the unity of far-flung regions under a common rule.

There were already different traditions. Some Christians celebrated Easter at the time of the Jewish Passover. Others observed it on Sunday near Passover. And how to calculate Passover according to the Roman calendar, not the Jewish calendar?

At the time, the Roman Empire followed a calendar established by Julius Caesar in 46 B.C. — the “Julian” calendar. It was a solar-based calendar that remains familiar today: a year of 365 days organized into 12 months of 30 or 31 days, save for February, which had 28 days. Every fourth year was a leap year, with an extra day added to February, as the actual orbit of the Earth around the sun took about 365¼ days.

The challenge of calculating Easter was how to fit the Hebrew and Julian calendars together. The Hebrew calendar assigns great weight to the lunar cycle. Passover was celebrated on the 14th day of the month of Nisan. 

The beginning of the Hebrew months depends upon the phase of the moon. Thus, for Easter to be celebrated in harmony with the recurrence of Passover — as during the original Holy Week — some formula had to be found for incorporating the lunar cycle into the Julian calendar. It was sufficiently complicated that different authorities in different regions disagreed, meaning Easter was celebrated at different times.

Nicaea found a solution. Passover was a springtime feast (in the Northern Hemisphere). The following formula was established and remains to the present day: Easter is the first Sunday after the first full moon (the lunar dimension) after the vernal equinox (the solar dimension). For calculation purposes, the Church fixed the date of the vernal equinox as March 21, even though the astronomical equinox can vary slightly. 

Thus, Easter can fall as early as March 22, if the full moon occurs on a Saturday equinox (March 21). In that case, Easter would be the next day, Sunday, March 22. 

Easter can be as late as April 25, if the full moon after the equinox is not until April 18, which, if a Sunday, means Easter comes on the next Sunday, April 25. 

The Nicaea solution took time to spread, but, eventually, the desired unity was achieved. The question of how to calculate Easter on the calendar was solved. 

Calendar Drift

A problem arose — very gradually. The formula was fine, but the calendar wasn’t. The Julian calculations fixed the year at 365¼ days, meaning an extra “leap” day every four years should keep things in order. But 365¼ days was about 11 minutes too long. Not significant at first, but over the centuries, it added up. 

By the time the Council of Trent met in 1545, the calendar was about 10 days out from where it had started, meaning that the astronomical equinox was falling on March 11 instead of March 21. Since March 21 had been fixed by the Church as the ecclesiastical equinox — the date used to determine Easter — this drift posed a serious problem. The council decided that the calendar should be corrected. This was finally accomplished by Pope Gregory XIII in 1582, nearly 40 years later, when he eliminated 10 dates from the calendar to restore the equinox to March 21. 

The changes came into effect in October. In 1582, people went to bed on Thursday, Oct. 4, and woke up on Friday, Oct. 15. A bit of Catholic trivia: St. Teresa of Ávila died on Oct. 4, 1582. That was already the feast day of St. Francis of Assisi, so she was assigned as a feast the day after she died — not Oct. 5, but Oct. 15.

A further refinement concerned leap years to deal with the 11-minute variance, which was necessary to prevent further drift. The extra day was eliminated in century years if they were not divisible by 400. For example, 1800 and 1900 were not leap years, but 2000 was. That fixed the problem.

Divisions Over Authority

The Council of Trent assumed responsibility for reforming the calendar based on the authority of Nicaea’s work in 325. But by the 16th century, there was no unified empire, no commonly recognized emperor, and a divided Christendom. In 1054, there had been the split between Catholic and Orthodox, and in 1517 the split between Catholic and Protestant. 

While Catholic countries accepted Pope Gregory’s reform — the “Gregorian” calendar — non-Catholic countries did not. Thus, moving around Europe meant not only a time change, but a date change of 10 days. A trip across the border from a Catholic country to a Protestant or Orthodox one meant moving 10 days on the calendar!

That was practically untenable, and despite divisions in Europe, the pope was the only one who could practically assert supranational authority. Eventually, Protestant countries accepted the Gregorian calendar, though it took a long time — Great Britain adopted it only in 1752, nearly two centuries later.

The Orthodox countries largely rejected the Gregorian reform, objecting that the reform was not a decision of the entire Church, but only its Western tradition. Even when Orthodox countries adopted the Gregorian reform for civil purposes, the Orthodox continued to follow the Julian calendar for religious feasts. Hence, Orthodox Christmas and Easter come after the Catholic/Protestant Christmas and Easter. Yet, because Easter is variable, some years the two dates do coincide. 

The approach of Nicaea had held in an unexpected way. In 325, the idea was that a united, nascent Christendom — the Church backed by state power — should have a united celebration of Easter. By the 16th century, Christendom was divided, with different churches backed by rival state powers. This was accordingly reflected in disputes about the celebration of Easter. 

An Ecumenical Opportunity?

Both Pope Francis and Ecumenical Patriarch Bartholomew of Constantinople have spoken in favor of a joint celebration of Easter. Beginning in the 1990s, and as recently as 2022, it was proposed that joint efforts might produce a common agreement by 2025, the 1,700th anniversary of Nicaea and a year when Easter would be celebrated on the same date. An important step took place in 1997, when the World Council of Churches issued its Aleppo Declaration, calling for a common date for Easter.

That initiative, largely Protestant, met a favorable reaction by those engaged in Catholic-Orthodox dialogue. Despite fervent statements of joint aspirations, and an agreement on the astronomical science of the equinox, it has not produced agreement.

Over the years, the most common proposals have been to fix a certain date, or for the “West” to simply adopt the Orthodox date. The most common fixed-date proposal has been for the Sunday after the second Saturday in April — which sounds like the way voting dates are set in secular constitutions. The United Kingdom Parliament passed the Easter Act in 1928 legislating that fixed-Sunday-in-April option, but it has never been implemented.

No joint effort on an issue as momentous as Easter can proceed without significant consensus in the Orthodox world. While Patriarch Bartholomew is the spiritual heir to the bishops of Constantine’s capital, his flock is numerically insignificant, numbering fewer than 20,000 souls. The majority of all Orthodox are Russian (100 million) or Ukrainian (28 million), out of some 220 million total.

The Russian Orthodox Church is now allied with an aggressive nationalist imperialism. It does not recognize the autonomy of the Ukrainian Orthodox. When Bartholomew recognized Ukrainian autonomy in 2019, Moscow “excommunicated” Constantinople. So regardless of what Constantinople decided regarding Easter, it would not be recognized by Moscow.

Unilateral Catholic action — simply adopting the Orthodox date — is not an option either, for unilateral action claiming universal application is one of the principal objections that Orthodox have to the Catholic approach to governance. 

A Spiritual Unity

While ecumenical unity is not likely, Catholics and Orthodox can unite spiritually at Easter, especially when it falls on the same date, as it does this year. Families that include both Catholic and Orthodox can provide a model of how to do so. 

In places where Orthodox and Catholic parishes are in proximity to each other, a common Easter offers opportunities for joint prayers and processions. Even if the Orthodox would not attend Catholic Mass, other devotionals might be options. For example, in many places, by local tradition, Catholics and Protestants join together for a public procession of the cross on Good Friday, or sacred music celebrations during Holy Week. Might Catholics and Orthodox do something similar?

The prayer of Jesus that “all may be one” was offered in the Cenacle on Holy Thursday, at a Passover meal. It will find greater resonance this Easter, in the anniversary year of Nicaea.