Today the Christians of the Middle East are celebrating the holiest day of their liturgical year. It is known by a variety of names, from “Paskha” among Greeks to “Resurrection” among Syriac– and Arabic-speaking Christians. “Easter” after all is a distinctly Germanic name for the festival, which in the Romance languages like French and Italian is called by names derived, like the Greek, from the Hebrew pesakh, “Passover“.
How did Middle Eastern Christians find themselves celebrating Christianity’s highest holiday five weeks after western European Christians observed their festivities? It’s a tale of two calendars, or rather more than two.
The ancient Jewish calendar was used, unsurprisingly enough, to observe Jewish festivals such as passover. The calendar was mostly a lunar calendar, with each month determined by the phases of the moon, running from new moon to new moon. But the seasons are determined by the solar year (or “tropical year,” based on the sun’s position relative to the tropics), which is about 11 days longer than a cycle of 12 lunar months. The ancient solution was to stick in a “leap month” every few years in order to keep the lunar months approximately aligned with the seasons, resulting in a “luni-solar calendar“. (The complexity of this system and the irregularity of the intercalated months led to the abolition of the “leap month” in the Islamic calendar, which is why Hijri years are approximately 11 days shorter than Western years and Ramadan cycles around the different seasons every 33 years or so. At a future point I will probably write a post on the many different calendars used in the Middle East.)
The old Roman calendar, in use at Rome before Rome headed an Empire, was some sort of lunar calendar, but the Julian calendar reform initiated by Julius Caesar was a strictly solar calendar with no reference to the moon (and most of whose months were slightly longer than a single lunar phase cycle). The new calendar was brilliantly simple: twelve months each with a fixed number of days (rather than a variable number of days determined by scanning the sky for the new crescent moon), with a single leap day every four years rather than a whole leap month every 2-3 years. Thus the Julian and Jewish calendars did not stand in fixed relationship, but shifted back and forth relative to each other.
The earliest Christians were heirs to both calendrical systems, and wished to commemorate annually the crucifixion and resurrection of Jesus, but when should such a celebration be? The earliest extant disagreement on the subject occurred already in the mid-second century, over the day of the week for the Easter celebration. Some early Christians advocated simply continuing to use the Jewish calendar, and they are known to history by the label (given them by their opponents) “Quartodecimans” or “fourteenth-ers”, because they reckoned the Passover on the evening of the fourteenth day (or the full moon) of the Jewish month Nisan. That was the date divinely assigned to Passover in the book of Exodus. Their opponents, however, insisted that since Christ rose from the dead on a Sunday, and Sunday was the day of gathering, so Christ’s resurrection should be celebrated on the Sunday following the Passover full moon. Both groups consulted the local Jewish community to determine which full moon would be the Passover full moon, but the “Sunday-only” group eventually won out.
By the fourth century Jews as well as Christians were working out computational rules to regularize the “leap-month” insertion, which required the Passover (14 Nisan) to fall on or after the Spring equinox (which, as the computations became more sophisticated, was specified to fall on 21 March regardless of when the astronomical equinox might occur). Thus the basic rule for the date of Easter was that it should fall on the first Sunday following the first full moon following the Spring equinox.
If one could calculate the date of the first full moon after the Spring equinox, then, one could determine when Easter would be. Ancient astronomy calculated that 19 solar years was equivalent to 235 lunar months (phase cycles), meaning that the date of the first full moon after the Spring equinox would repeat every 19 solar years. This is the Metonic cycle. (Of course the ancients had not observed the length of either solar years or lunar phase cycles with the precision that would become possible with more sophisticated technology, but their calculations were very nearly exact, off only by around 0.001%!) The date of Easter could then be determined as falling on the following Sunday. Since the day of the week of 21 March follows a 28-year cycle (due to leap years every four years in the Julian calendar), the total cycle of Easter dates in the Julian calendar repeats every 28 * 19 = 532 years.
Unfortunately the Julian calendar itself was not perfectly accurate, but was too long by approximately 1/120 of a day (12 minutes). This was brief enough to be unnoticeable in a single lifespan (the oldest living person today would have the seasons starting a day earlier in the Julian calendar compared to when he was born), but as the centuries progressed, the observed Spring equinox moved further and further ahead of the date used in computation, 21 March. By the 1500s, new astronomical calculations were showing that the length of the solar year was a tiny amount less than 365.25 days, the value presumed by the Julian calendar. Pope Gregory XIII sponsored a calendar reform which involved moving the date forward 10 days, and then to keep the calendar more firmly in place, skipping one leap day every century except every four centuries (which is why the year 2000 was a leap year, but 1900 was not).
The resulting year length was much closer to the average length of the solar year, but human history has never worked exclusively on the basis of scientific calculations. In 1582, when Pope Gregory XIII decreed the adoption of the new revised calendar, Europe was embroiled in bitter religious conflicts between Catholics and Protestants, and to the Pope’s detractors (of which he had many) the “Gregorian calendar” was simply the latest demonstration of papal abuse of power. Even Catholic monarchs took a few years to get behind the new calendar, while England refused to adopt the calendar devised by the pope until 1752, almost two centuries after it was proposed. In the interim, Europe was divided between two dates initially 10 days apart, but slowly growing…
(As an interesting aside, one of the members of the papal commission which developed the calendar reform proposal was the former Patriarch of the Syriac Orthodox Church, Ignatius Ni’mat Allah, who had moved to Rome after abdicating.)
While most Middle Eastern Christians have been compelled by political necessity to use the Gregorian calendar (and the Hijri calendar) for everyday affairs, Orthodox Christians still do not see why they should follow a reform instituted by a pope whom they reject. They still use the Julian calendar for calculating the date of Easter, even if they might use the Gregorian calendar for less important church festivals. Today is not 5 May in the Julian calendar, but April 22. The Metonic cycle has also gotten out of step with actual full moons, so the old way of calculating asserts that the first full moon after 21 March Julian (= 3 April Gregorian) took place on 17 April Julian (= 30 April Gregorian), last Tuesday, rather than the actual occurrence shortly before midnight on 25 April Gregorian (= 12 April Julian). Thus today is the first Sunday after the putative full moon according to the ancient Metonic cycle following 21 March Julian, the putative Spring equinox.
Because Eastern and Western dates for Easter always fall on Sundays, sometimes they coincide, sometimes they differ by 7 days, and sometimes by 35 days. They differ by 35 days when the putative full moon according to the Metonic cycle falls after 21 March Gregorian but before 21 March Julian, so that they are based on different lunar months. That is what happened this year. They differ by 7 days when the actual full moon occurs after 21 March Julian, but late enough in the week that the predicted full moon according to the Metonic cycle falls on or after the Sunday following the actual full moon. They coincide only when both of these sources of error do not occur, namely when the actual full moon occurs after 21 March Julian (April 3 Gregorian) and early enough in the week.
Various reform measures have been proposed to reunify Eastern and Western dates for celebrating Easter, just as various reform measures have been proposed to reunify Eastern and Western Christianity, but none have been adopted long-term. Until that happens, Middle Eastern Christians will occasionally celebrate Easter on Cinco de Mayo, we all can wish our Middle Eastern Christian friends an ‘eid mubarak (عيد مبرك, “blessed festival”), and remember the metropolitan archbishops of Aleppo who are still missing from their cathedrals on this holiday.