A ZENIT DAILY DISPATCH
Why Dates of Easter Differ

ROME, 29 MARCH 2011 (ZENIT)
Answered by Legionary of Christ Father Edward McNamara, professor of liturgy at the Regina Apostolorum university.

Q: I am an Orthodox reader and I have a question. As you know, the Catholic (Western) Churches and the Orthodox celebrate Pascha [Easter] on different Sundays most of the time. The rule of the Council of Nicaea says, "The first Sunday after the first full moon after the vernal equinox." However, in the notes on the council it tells us that, even using this calculation — there being no common calendar in the empire at the time — Christian churches were celebrating the feast on different Sundays based on when they calculated the equinox and full moons based on their particular calendars. To have unity within the empire, Constantine added the caveat, "But shall not precede or coincide with Passover," and for more than 1,000 years, this worked and we all celebrated Pascha on the same Sunday. Then with the introduction of the Gregorian calendar this changed somewhat but, even if the imperial order was still honored in the West, we would still be celebrating Pascha together. Can you tell us why the Western Churches have chosen to neglect this order and will celebrate Pascha before or during Passover, as they did this year, while the Orthodox will still honor the rule and wait? Or can you tell us why the West, as is the case in some years, will celebrate Pascha on the Sunday when the full moon is Saturday night, which liturgically is Sunday? — G.J., Houston, Texas

A: First of all, it would appear that the supposed rule that Easter must be celebrated after Passover does not hail from the Council of Nicaea. It would appear that this provision was first proposed by the 12th-century Byzantine canonist Joannes Zonaras. It probably stems from the fact that the drift caused by the Julian calendar's miscalculation of the solar year means that Easter now always falls after the start of the Jewish Passover. The fact that this happens gave rise to the belief that this was a rule, but the historical evidence does not seem to support this.

As our reader points out, early Christians calculated Easter using different criteria. Christians in Syria generally held Easter after the Jewish Passover whereas most other Christians within the Roman Empire calculated Easter with no thought for the Jewish festival. Thus Easter was often celebrated on different days in Antioch and Alexandria. Nicaea decreed a single date but left no precise indications regarding the criteria for calculating the date. It was only several decades later that the system used in Alexandria became generally accepted.

We had already dealt briefly with the question of the date for Easter on Feb. 28, 2006. Our present reply will flesh out what we said on that occasion.

Easter follows a lunar-solar, rather than a solar, calendar and is celebrated on the Sunday that follows the first full moon after March 21, the vernal (spring) equinox. Therefore, Easter cannot fall earlier than March 22 or later than April 25.

Thus, according to a detailed article in Wikipedia, "Gregorian Easter can fall on 35 possible dates. ... It last fell on March 22 in 1818, and will not do so again until 2285. It fell on March 23 in 2008, but will not do so again until 2160. Easter last fell on the latest possible date, April 25, in1943 and will next fall on that date in 2038. However, it will fall on April 24, just one day before this latest possible date, in 2011. The cycle of Easter dates repeats after exactly 5,700,000 years, with April 19 being the most common date, happening 220,400 times or 3.9%, compared to the median for all dates of 189,525 times or 3.3%."

Most of the Eastern Churches follow the same basic principles but often celebrate Easter on a date different from Catholics and other Western Christians because they continue to follow the calendar of Julius Caesar without the corrections incorporated by Pope Gregory XIII in 1582.
Julius Caesar's calendar (from 46 B.C.) calculated the year as 365 days and 6 hours and thus was about 11 minutes and 9 seconds more than the Earth's actual course. Although tiny, this excess puts the calendar off by a day, more or less, every 128 years. Thus, the Council of Nicaea already found it necessary to regress the date of the spring equinox to March 21 instead of the original date of March 25.

By the time of Gregory XIII the difference had grown so much that the spring equinox occurred on March 11.

In 1581 with the bull "Inter Gravissimas" Pope Gregory promulgated a widespread reform which, among other things, re-established the spring equinox on March 21 by eliminating 10 days from October 1582. Coincidence would have it that St. Teresa of Avila died on that very night of Oct. 4-15.

The error of Julius Caesar's calendar was corrected by deciding that the turn of the century — always a leap year in the Julian calendar — would be so only when the year could be divided by 400, that is 1600, 2000, 2400, 2800, etc., whereas there would be no leap year in the others.
Most Catholic countries, and even some Protestant ones, accepted the reform almost immediately. Some countries, such as England, held off accepting the papal reform until 1752 while Russia did not adopt it until after the Communist takeover in 1918.

The calculation is still not perfect as there is still a difference of 24 seconds between the legal and the solar calendar. However, 3,500 years will have to pass before another day is added.
Although all Western countries now use the Gregorian calendar for civil purposes, most Oriental Churches continue to use the Julian calendar to calculate Easter. The difference between the two systems is now 13 days, so that although the Orthodox Easter also falls between March 22 and April 25 (inclusive), these dates correspond to between April 4 and May 8 (inclusive) in the Gregorian system.

This article has been selected from the ZENIT Daily Dispatch
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