(avg. read time: 5–10 mins.)
We have already noted the difference between the Julian year (365.25 days) and the tropical year (365.2422 days). In more practical terms, this difference translates to about eleven minutes and some change (about fourteen or fifteen seconds) every year. This difference created a drift in the calendar between the dates marking the equinoxes and solstices and the astronomical equinoxes and solstices. Given how Easter was calculated relative to the vernal equinox, this meant that the date of Easter would drift from the actual vernal equinox until later and later in the year. By the time of 1582, the difference between the vernal equinox according to the Julian calendar and the vernal equinox according to astronomical observation of the tropical year was about ten days (today, it is thirteen). As such, the celebration of Easter and its timing were so crucial that the corrections needed for the holiday produced the greatest calendrical shift in the Christian era of the West after an investigation posing the basic question: How can we get back on the right track?
To devise a solution to get the calendar into proper alignment for the celebration of Easter, Pope Gregory XIII appointed a commission in approximately 1572 for calendrical reform consisting of clerics, astronomers, mathematicians, and a lawyer (as a change in the calendar would have legal consequences). The ultimate architect for the solution was the late Aloysius Lilius (or Luigi Lilio/Luigi Giglio), an astronomer and mathematician. His work was presented to the commission by his brother Antonio. The actual manuscript of his work was never printed. It only survived in the summary Compendium novae rationis restituendi kalendarium. When the commission presented their solution based on his work to Gregory, he issued the papal bull Inter gravissimas.1
The long-term reform was to shorten the calendrical year to an average of 365.2425 days, which was accomplished by dropping the leap day during centennial years, except those that are evenly divisible by 400 (e.g., 1600 still had the leap day, but 1700 did not; 9). This brought the mean calendrical year into better alignment with the mean tropical year (365.2425 days compared to 365.2422 days) so that the difference between the two was a matter of seconds. The immediate reform, to make up for the ten-day shift, was that October 4 of 1582 would be immediately followed by October 15 (7). That Easter was crucial to these decisions is evident in sections 2, 6–7, and 10, especially in 6, when the pope outlines the three things necessary for the restoration of Easter:
First, the precise date of the vernal equinox, then the exact date of the fourteenth day of the moon which reaches this age the very same day as the equinox or immediately afterwards, finally the first Sunday which follows this same fourteenth day of the moon. Therefore we took care not only that the vernal equinox returns on its former date, of which it has already deviated approximately ten days since the Nicene Council, and so that the fourteenth day of the Paschal moon is given its rightful place, from which it is now distant four days and more, but also that there is founded a methodical and rational system which ensures, in the future, that the equinox and the fourteenth day of the moon do not move from their appropriate positions.
With the help of one of the members of the commissioned group, the mathematician Christopher Clavius, who wrote seven works defending and explicating this reform (most completely in his Romani calendarii a Gregorio XIII restituti explicatio [1603]), this Gregorian calendar came to be the dominant civil calendar throughout the world to this day. However, even in many countries where it became the civil calendar, the ecclesial calendars of the Eastern Orthodox and most of the Oriental Orthodox are still Julian calendars, leading to divergences in both the celebration of Christmas and Easter.
Despite the technical errors of the Julian calendar, Easter calculations based on it came the closest to achieving the common vision of the Synod of Arles and the First Council of Nicea. Although the process took centuries to sort out, for many years most of the Church worldwide could claim to celebrate Easter on the same day, even after the Great Schism of 1054 or the Protestant Reformation of the early sixteenth century. But the widespread adoption of the Gregorian calendar for both civil and ecclesial purposes has created a rift with those traditions that remain dedicated to the Julian calendar that the Church has referenced since the ancient days. Teodor Dumitru Vãlcan calculated the Easter dates for both Gregorian and Julian calendars from 1583 (when the divergence in Easter dates began) to 2499 and determined that the 917 dates agree 256 times (27.9%), diverge by one week 404 times (44.1%), or diverge by as many as four (27; 2.9%), five (228; 24.9%), or six weeks (twice; 0.2%).2
Various calls and proposals have been made to attempt to establish a new common date for Easter, to reunite the Western and Eastern reckonings. Most famously, the World Council of Churches and the Middle Eastern Council of Churches at their meeting in Aleppo, Syria in 1997 made such a proposal.3 The members reviewed the theological rationale for celebrating Easter, reviewed the history of Easter computation, and considered the Nicene directives as well as the historical connections with Passover. Afterwards, the consultation made two recommendations.
1) The date of Easter should maintain the Nicene norms, calculate the astronomical data as accurately as possible with the tools available, and use the meridian of Jerusalem as the basis for reckoning, since this was the location of Jesus’s death and resurrection (11). As they noted, experts in astronomy had already provided the necessary calculations in Synodica V (Chambésy - Genève, Les Editions du Centre Orthodoxe, 1981), 133–149. Of course, this change would have more effect on many of the Eastern traditions than on the Western ones. One will notice in the table attached to the document, which charts Easter dates from 2001 to 2025, that the Aleppo date of Easter agrees with the Gregorian calendar every year except for 2019, when this table assigned the date of March 24 against the Gregorian April 21 and the Julian April 28. Conversely, it never agrees with the Julian calendar against the Gregorian one, and it only agrees with both seven times. They realized this extra burden on the East and so had this to say on the matter:
The consultation is well aware of the particular circumstances of many eastern churches. In some countries in the Middle East and Eastern Europe, where the Christian churches have lived with the challenge of other religions or materialistic ideologies, loyalty to the “old calendar” has been a symbol of the churches’ desire to maintain their integrity and their freedom from the hostile forces of this world. Clearly in such situations implementation of any change in the calculation of Easter/Pascha will have to proceed carefully and with great pastoral sensitivity. (14)
2) The churches should undertake a period of study and reflection with the goal of implementing a common Easter date along the aforementioned lines by 2001. That year would also provide an opportunity for the WCC and its collaborators to reconvene on this matter to assess reactions and progress towards this goal. Given the content of the second recommendation, it is likely that the reader has already figured out what basically happened. As noted already, the suggestions would put more of a burden on the Eastern churches than on the Western ones and the devotion of the East to its Julian traditions—despite the attempts of the Pan-Orthodox Congress of Constantinople in 1923, or the support from the North American Orthodox-Catholic Consultation and the U.S. Orthodox-Lutheran Dialogue, among others, for the Aleppo Statement of 1997—remains strong. For better or worse, they remain committed to the calendar of ancient Church tradition, to the calendar of Nicea. The likelihood of Eastern Orthodox acceptance (or the majority of Oriental Orthodox for that matter) of these suggestions does not seem to be high as of now.
In addition to the Julian churches’ insistence that they are abiding by the traditional calendar and are thus more aligned with ancient practice, they also justify their practice through reference to the aforementioned Zonaras Proviso, that their dates for Pascha always fall after the Jewish Passover (which, again, they tend to assume is limited to the day of Passover, as has been my typical definition here, rather than the merged and extended festival of Judaism today). In contrast, the Gregorian churches argue that they are more in line with the rationale of ancient tradition because they more accurately observe the timing of the vernal equinox and thus of the Paschal full moon and the Paschal Sunday that depend on the timing of that equinox. They operate on the assumption that their forebears would correct the ecclesial calendar as they have if they were confronted with the long-term shortcomings of the Julian calendar.
Summary
The timing for when Christians celebrate Easter/Pascha has historically been tied to the Passover, since all the Gospels record Jesus’s resurrection as being on the first day of the week after Passover. While Christians were initially divided as to whether to celebrate their own Pascha the same day as the Jewish feast or to celebrate it on the Sunday afterwards, the majority already sided with the Sunday tradition by the end of the second century. As Christians eventually became independent of the Jewish reckoning, especially after the Council of Nicea, a long debate ensued as to how to calculate the date of Pascha properly given the established parameters: a method must map the date of Passover (determined by the lunar calendar) on the Julian calendar (a solar calendar) and the date must be on a Sunday after the fourteenth moon (the Paschal full moon) on or after the vernal equinox. As such, the consensus came to be that the allowable range of dates for Pascha was from March 22 to April 25, between the fifteenth and twenty-first moon of the cycle during or after the equinox (if the equinox occurs after the fourteenth moon in the current cycle), and that the best way to forecast such dates was through the nineteen-year cycle (multiplied to ninety-five or even 532 years) as articulated by Anatolius and Dionysius Exiguus, and as explicated by the Venerable Bede. Unfortunately, due to the problems of the Julian calendar on which these calculations were based, the calculated vernal equinox was drifting from the actual vernal equinox, which motivated the Gregorian reform and led to the existence of the current Gregorian calendar. Both Christians who use the Gregorian calendar and Christians who use the Julian calendar still abide by the parameters for Pascha/Easter as both still celebrate it somewhere between the fifteenth and twenty-first moon and somewhere between March 22 and April 25. However, due to the (currently) thirteen-day difference between these calendars, the Julian dates translate to being between April 4 and May 8 on the Gregorian calendar. Despite ecumenical efforts to reconcile these different reckonings, the Church continues to celebrate the day of Jesus’s resurrection according to different calendars and calculations.
Teodor Dumitru Välcan, “Solving Two Problems Related to Determining the Date for Easter,” Astra Salvensis 5.9: 39–44.