A Puzzle About the Date of Pascha:  Part I

an article by Dr. Richard Otte in the

11 April 2025 issue of PublicOrthodoxy

In the early Church there was no uniform or standard day on which the Resurrection was celebrated, and the First Ecumenical Council at Nicaea decided all Christians should celebrate the Resurrection on the same day.  Although not part of any official document produced at Nicaea, the letters written to the churches contained a formula for what day the Resurrection should be celebrated:

The first Sunday after the first full moon after the vernal equinox.

This formula gives a unique date for the celebration of the Resurrection, and it was unproblematic for many years.   However, it is well-known that the Eastern and Western churches now often celebrate Pascha and Easter on different days (I use the term “Pascha” to be the celebration of the Resurrection by the Eastern churches, and “Easter” to be the celebration by the Western churches).   In what follows I raise a puzzle for the common explanation as to why the churches sometimes celebrate Pascha and Easter on different days.

One often hears that although the Western churches and Eastern churches use the same above formula to calculate the dates of Pascha and Easter, when the dates of Pascha and Easter differ it is due to the Western church using the Gregorian calendar and the Eastern church using the Julian calendar.  For example, Metropolitan Saba of the Antiochian Orthodox Church recently wrote that both the Eastern and Western churches accept the Nicene formula, and the difference in these dates is due to the calendars used:

“It is a difference in the type of calendar, not in the rule.  In the first fifteen centuries, Christians followed what we know as the Old, or Eastern, or Julian calendar.   In the Sixteenth Century, Pope Gregory XIII of Rome commissioned an astronomical correction of that calendar, which became known as the corrected, or Western, or Gregorian calendar” [The Word, May -June 2024, p 6].

On this standard view both the Eastern and Western churches accept the Nicene formula, but can get different dates because they use different calendars.  Notice that the Nicene formula contains three parts:   two of them based on astronomical events (full moon an vernal equinox) and one based on a calendar event (Sunday).   This immediately gives rise to a puzzle.  The Julian and Gregorian calendars agree on day of the week, so Sunday on the Julian calendar is also Sunday on the Gregorian calendar.   But if the only calendar specific part of the Nicene formula is a reference to Sunday, and the Julian and Gregorian calendars agree on what days are Sundays, then how could the different dates of Pascha and Easter be due to the use of different calendars?   In other words, if none of the information input into the formula differentiates between the Julian and Gregorian calendars, how can the output be dependent on the calendar used?

Let us restate this puzzle in a different way:  the puzzle arises because if the Western and Eastern churches both apply the same Nicene formula, and both the Julian and Gregorian calendars agree on the only calendar dependent part of the Nicene formula, they then should come up with the same dates of Easter and Pascha. The date of the vernal equinox is an empirical astronomical matter,  as is the full moon.   These are determined empirically and are not dependent on any calendar at all; one could determine when the vernal equinoxes and full moons occur even if one did not have a calendar.  So, if people using the Gregorian and Julian calendars  agree on when the astronomical events occur, and agree on what days are Sundays, then they should celebrate Pascha and Easter on the same dates.   The different dates of Pascha and Easter is not due to the Eastern and Western churches using the same formula but different calendars.  It must be due to something else.

To help us get clearer about this puzzle, consider the following  experiment.  Suppose that archeologists discover original documents from the Council of Nicaea, and in addition to the material on the way to celebrate Pascha, there immediately followed material on what time liturgies should start on Sunday mornings.  Evidently members of the Council were concerned that visitors to a town might not know when Sunday liturgy would start, and to avoid any confusion, the Council decided that liturgies on Sundays should start at the same time:

Sunday liturgies should begin three hours after local sunrise.

This formula has the advantage that anyone could determine when liturgy would start on a given Sunday.  Notice that this formula depends on an empirical event:  local sunrise.

Now suppose that at some point the Church declares that sunrise always happens at 6:30 AM local time.  Perhaps the Church even calls this “ecclesiastical sunrise” and uses this with the Nicene formula to have all the churches have Sunday liturgies begin at 9:30 AM. In doing this, the church has changed the original Nicene formula.   The new formula is

Sunday liturgies should begin three hours after the ecclesiastical sunrise (6:30) AM).

The original formula based starting times on an empirical observable event whereas the modified formula bases starting times on a specific time on the clock, 6:30 AM.  Since actual sunrise is not always at 6:30 AM, these formulae can give different times for when Sunday liturgies should begin.   It is clear in this example the Church changed the original formula that was given by the Council at Nicaea.

Returning to the dates of Pascha and Easter, the difference is that at some point the Church assumed that the vernal equinox occurs on March 21 of each year on the Julian calendar.  This results in a new formula for the date of Pascha:

The first Sunday after the first full moon after March 21 on the Julian calendar.

This is analogous to the Church declaring a fixed time for local sunrise in our thought experiment.  In both cases, the Church stipulated an empirical astronomical event happens at a specific day or time.   In the case of Pascha, this new formula ties the date of Pascha to a specific date on the Julian calendar, even though the original formula of Nicaea was calendar independent.   Notice that one could use the Julian calendar and follow the original Nicene formula; one would base the date of the vernal equinox on empirical matters and not stipulate that it occurs on a certain date on the calendar. If so, churches would celebrate Pascha and Easter on the same day.  This explains why the puzzle arises.

(Conclusion next week)