Astronomical Truth: Science Offers Common Easter Date for East and West

How can the fractured unity between Catholics and Orthodox Christians be resolved regarding the question of when to celebrate this day of all days in the Christian calendar?

Illarion Pryanishnikov, “Easter Procession”, 1893
Illarion Pryanishnikov, “Easter Procession”, 1893 (photo: Public Domain / Public Domain)

Deacon Jeffrey Mierzejewski and his family usually celebrate Easter on two Sundays each year. This year, the deacon and his wife, Kseniya, and their four children celebrated Easter on April 4, and a month later they celebrated it on May 2. 

Deacon Mierzejewski is a member of a Byzantine Catholic community that meets at Holy Cross Catholic Church in Austin, Texas, and Kseniya, who is Eastern Orthodox, attends the Divine Liturgy at a local Orthodox church. 

But after 35 years of marriage, the Mierzejewskis have learned through the compromises that spring from love to accommodate their respective traditions in celebrating the Pascha (the Eastern Christian term for Easter).

“Generally speaking, we celebrate both Paschas,” Deacon Mierzejewski told the Register, “and that means we would, most years, go to the celebration of the Pascha back into Lent for a couple weeks. More or less, we negotiate and do the best we can.”

The Mierzejewskis’ experience of Easter reflects nearly half a millennium of fractured unity between Catholics and Orthodox Christians on the question of when to celebrate this day of all days in the Christian calendar.


Julius Caesar vs. Pope Gregory XIII

The Latin Rite and most Byzantine and other Eastern Catholic Churches celebrate Easter as determined by the Gregorian calendar, while the Orthodox Churches — with a few exceptions — celebrate Easter as determined by the older and less accurate Julian calendar. 

The Julian calendar, which was formulated by Julius Caesar in 46 B.C. (and was itself a reform of an earlier Roman calendar), calculates a solar year to be 365.25 days. This overestimates the year’s actual length by about one day each century. Sixteen centuries later, this accumulating “drift” meant the spring equinox was occurring long before its March 21 date on the Julian calendar.

The Gregorian calendar was introduced in 1582 by Pope Gregory XIII to correct this miscalculation. By reducing the solar year to 365.2425 days and adjusting leap years accordingly, the Gregorian calendar achieves much greater accuracy in calculating the spring equinox — and thereby, the date of Easter. 


Theology and Horology

While most of the world eventually accepted the Gregorian calendar, many within the Orthodox Churches still do not — at least when it comes to Easter. Do they reject the Gregorian calendar to preserve theological perspectives and liturgical traditions or because, despite being scientifically more accurate, the Gregorian calendar was a papal initiative? This is a central question in discussions about a common date for Easter between Catholics and Orthodox Christians.

Yet, like the Mierzejewskis, the Eastern and Western Churches have shown abundant goodwill in seeking to resolve the division. Catholics and Orthodox have made many attempts over the years to propose a common fixed date or range of dates for Easter. But for Catholics who have studied the question and engaged in dialogue with the Orthodox on the issue, the question has less to do with the eternal truths of the faith than it does with the science involved in calculating time. 

Furthermore, those who have studied the question see that while establishing a common Easter date might be an important symbolic step in ecumenical relations between East and West, the issue is more complicated than a calendric compromise.  

Nonetheless, for both practical and theological unity, Catholic and Orthodox generally agree that a common Easter date is desirable and more in keeping with the First Ecumenical Council of Nicaea in 325, which mandated the first Sunday after the first full moon following the spring equinox (between March 22 and April 25) as the common Easter date for all of Christendom. 

The Council reasoned that Christ’s passion and resurrection took place at the time of the Jewish Passover, the 15th day of Nisan in the Hebrew Calendar, during which the first full moon of the spring equinox will often — but not always — occur. But because Passover may occasionally occur after the second full moon (among other reasons), the Council of Nicaea decreed that the Church would determine the date of Easter according to the spring equinox (March 21 as the fixed normative date on both the Julian and Gregorian calendars) rather than by the less precise dating of Passover. 


Parallel Paschas

Most recently, this past March, Catholics and Orthodox renewed their desire to establish a common Easter date. The president of the Pontifical Council for Christian Unity, Cardinal Kurt Koch, and Orthodox Archbishop Job Getcha of Telmessos, Greece, a representative of the Patriarchate of Constantinople to the World Council of Churches (WCC), voiced support for resolving the matter. Catholic News Service reported that Archbishop Getcha saw 2025, the 1,700th anniversary of the Council of Nicaea, “as a good year to introduce this reform of the calendar.”

The last major ecumenical effort to resolve the issue took place during a pair of meetings in the late 1990s. From March 5-10, 1997, Orthodox and Protestant representatives met in a consultation sponsored by the WCC and the Middle East Council of Churches in Aleppo, Syria, to take up the issue of a common Easter date. The event resulted in “The Aleppo Statement,” which encouraged Christian communities around the world to agree to a common Easter date. 

The following year, from Oct. 29-31, 1998, the North American Orthodox-Catholic Theological Consultation for the United States (NAOCTC) held a similar consultation, which included 12 Catholic and 12 Orthodox representatives. Co-sponsored by the U.S. Conference of Catholic Bishops and the Assembly of Canonical Orthodox Bishops of the United States of America, the 1998 consultation affirmed “The Aleppo Statement” in its Oct. 31 report, “Common Response to the Date of Easter/Pascha.” 

“The Aleppo Statement is faithful to the decisions of the First Ecumenical Council [of Nicaea] regarding the date of Easter/Pascha,” states the report. “At the same time, it takes into account the contemporary situation, which calls for a common witness to the resurrection of our Lord Jesus Christ, the central mystery of the Christian faith. Our consultation therefore urges our churches to give serious consideration to its recommendations.”

Father David Petras, a professor of theology at the Byzantine Catholic Seminary in Pittsburgh before retiring in 2013, served on the 1998 consultation team. The first Byzantine Catholic invited to join the NAOCTC, he was surprised during the 1998 discussions to see both sides agree that the science of the question was paramount.

“All the Orthodox members of our consultation,” he told the Register, “advocated going to the Gregorian calendar for one simple reason: The calendar is more accurate, scientifically — it keeps the date of the vernal equinox on March 21.”


Time for Science

For Father Petras, finding a common Easter date is less a matter of theology or ecclesial politics — although these both play a part in the current dialogue about the issue — and more about the science involved in determining the date.

“I think the central issue is simply this: It is a question of Church policy vs. science,” he said. “Church policy, of course, was the original problem with the Orthodox because the Gregorian calendar was mandated by our pope, and therefore they instinctively said, ‘No’ — and have instinctively said, ‘No’ ever since. But it’s simply a matter of science that the vernal equinox occurs when it occurs. It doesn’t matter whether someone’s Catholic, Orthodox, atheist or otherwise.”

To complicate matters, even Eastern Churches — both the Orthodox and the Byzantine Catholics — are not unified on the calendar issue, Father Petras noted. 

While Byzantine Catholics in the United States adopted the Gregorian calendar, he said, in parts of the world where their neighbors are all Orthodox, some Byzantine Catholics choose for ecumenical reasons to celebrate Easter according to the Julian calendar.

But diplomacy aside, Father Petras added, “most arguments for the continuation of the Julian calendar now are that this is a religious faith decision, and those who follow it are separating themselves from the secular world. The secular world follows the Gregorian calendar, and the [Orthodox] Church follows the Julian calendar. This is not entirely true, of course, because more than half the Orthodox Churches use the Gregorian calendar for their fixed days [such as Christmas], but none use it to fix the day of Easter, except for the Orthodox Church in Finland, which follows the Gregorian calendar for Easter.”

According to the Greek Orthodox Archdiocese of America, the Orthodox Church in Finland “makes up less than 2% of the population of a predominantly Lutheran country,” and therefore “it observes Easter according to the [Gregorian] Calendar for practical reasons.” 


Unintended Consequences?

Before the consultations in the late 1990s, the question of a common Easter date was raised most prominently at the Second Vatican Council. In an appendix to Sacrosanctum Concilium, the Council’s document on the liturgy, the Council Fathers welcomed the idea of a single fixed Sunday as the date for Easter, saying, “The Sacred Council would not object if the feast of Easter were assigned to a particular Sunday of the Gregorian calendar, provided that those whom it may concern, especially the brethren who are not in communion with the Apostolic See, give their assent.”

But according to Lynne Boughton, adjunct professor at The Liturgical Institute at the University of St. Mary of the Lake in Mundelein, Illinois, even if Catholics and Orthodox accepted such a proposed common dating for Easter, other problems would have to be addressed. 

For instance, she told the Register, such a change in dates would affect liturgical texts by “eliminating the expectation that the date of Easter Sunday can vary, in both Catholicism and Orthodoxy, over a five- to six-week course for any given year.”

The Roman Missal — in both the ordinary and extraordinary form — and equivalent Eastern Catholic and Orthodox texts, she said, “would need to undergo the expensive process of being substantially redesigned and republished to accommodate the extensive change in the calendar.”

Not only would propers, antiphons and readings need to be changed, she added, but any proposed fixed date (or even narrow range of dates) for Easter would have a ripple effect on other feasts, such as the Ascension, and other seasons, such as Pentecost, “whose periods of observance circulate through the calendar in relation to Easter.”

“Instead of being the ‘axis’ of the liturgical year, around which all other seasons are configured,” Boughton noted that, in a fixed-date solution, “Easter Sunday would become just another solemnity.”


Back to Nicaea

But if science is the key to the solution, the authority to use that key can be found most clearly in the Council of Nicaea. Both Catholics and Orthodox recognize the decrees of this council as valid and binding on the faithful. 

In an essay on the history of the Nicene Council, John Fotopoulos, associate professor of New Testament studies at St. Mary’s College in Notre Dame, Indiana, notes that long before the Gregorian calendar had been devised, the Council of Nicaea indicated the importance of science in determining the Easter date. It was a calculation less accurate, in retrospect, since it relied on the Julian calendar, but it was following the method used by the Church in Alexandria, which at the time was renowned for its scientific study of the heavens. 

“Because Alexandria, Egypt, was known as a premier center of astronomy in the ancient world, the Church of Alexandria came to assume responsibility in the Eastern Church for making scientific calculations used to determine the date of Pascha,” he writes, adding, “Nicaea did not precisely regulate the technical details, methods, or calendar by which the vernal equinox and vernal full moon would be determined, but expected the best available science to be used for the calculation of Pascha.”

In a similar way, Boughton noted, the Gregorian calendar was devised not as a wholly new measure of the solar year, but, since it proved to be “the best science available” at the time, it simply corrected inaccuracies within the Julian calendar.

Historically, according to Boughton, Rome was never concerned about whether the Church in the East or in the West determined the date for Easter — as long as the science proved sound.

“In fact,” she said, “Pope Leo I [pontificate from 440 to 461] admitted, 1,100 years before the Gregorian calendar existed, that Alexandrian priest-astronomers were providing more suitable calculations according to Nicaea’s directive than their counterparts in Rome.”


Easter Hopes

Meanwhile, the celebration of “two” Easters remains a fact of life for Christendom — and for the Mierzejewskis in particular. 

Deacon Mierzejewski, who was trained as an astronomer after taking a degree in mathematics and computer science, sees science and theology agreeing on the matter of the correct date for Easter. 

“The Sunday after the first full moon after the vernal equinox ties God’s actions in the passion and resurrection of Christ to the natural world, to the solar cycle, the monthly cycle,” he said. “It’s a well-defined place that ties things together.”

Nonetheless, he added, “I understand there are a lot of identity issues tied up among Orthodox Catholics with the date, and for that matter, for them celebrating all on the same day. They feel strongly that changing that day — and having some Orthodox Churches change it and some not — would be a great loss. I can sympathize with that.”

At the same time, Father Petras said, an Easter Sunday celebrated by all Christian creeds in common would speak volumes to the rest of the world.

“I don’t think that it’s fatal to Christian unity to have different Easter dates,” he said, “but the point is that the resurrection of Our Lord is the very center of all Christian faith, and it would be good for all Christians to observe this commemoration on the same date.”