Sunday, April 13, 2008

Dating Easter

Most of North America's Christians are now three weeks past Easter. Roman Catholics, Protestants, and Anglicans, as well as members of the Armenian Apostolic Church, all celebrated Easter very early this year, on 23 March. Meanwhile, it is still one week until Passover and two weeks until Orthodox Easter. I am still looking at two more weeks of fasting, while my Anglo-Catholic friends are already half-way to the Ascension!

It has long been a principle of the Church that all Christians should celebrate the Resurrection on the same day. A number of councils, such as the Synod of Whitby, tried to get all the Christians in a region on the same page with respect to the date of Easter. How did we get to the current anomalous situation?

The early rule adopted by the Churches of Rome and Alexandria was that Easter should be observed on the first Sunday after Passover. Passover, the 15th of Nisan on the Jewish calendar, would normally fall on the day of the first full moon on or after the vernal equinox. At that time the date of Passover, as observed by rabbinical Jews, depended upon observation of nature, not computation.

The Roman version of the rule ensured that Easter would always be observed after Passover. If Passover fell on Sunday, then Easter would be celebrated on the following Sunday. This was motivated in part by history: According to the Gospel of John (e.g., 19:31), the Crucifixion occurred on Friday, Passover was observed on Saturday, and the Resurrection occurred on Sunday. Therefore, they reasoned, Easter should be observed after Passover. But it might also have been motivated in part by an anti-Jewish attitude that was prevalent among Christians of some regions, who preferred to separate the Christian Passover (Greek Pascha) from the Jewish Passover (Hebrew Pesach).

To complicate matters, around that time, the Jews reformed their calendar to simplify the determination of when to add an intercalary month (a 13th month to keep the lunar calendar in sync with the solar calendar). Formerly, the Sanhedrin would announce the insertion of the extra month based on four factors: the equinox, the ripeness of the barley and of the fruits of trees, and the birth of sufficient lambs for the Passover sacrifice. The new calendar, traditionally attributed to the 4th-century rabbi Hillel II (though more likely adopted gradually between the 1st and 9th centuries) was rule-based rather than astronomical. The dispersion of the Jews all over the Mediterranean world made it difficult to communicate the beginning of the ecclesiastical New Year (1st of Nisan) to everyone. The new calendar was intended to ensure that all Jews could start the new year together, and thus celebrate Passover and other festivals together. But the rule-based calendar sometimes departed from the celestial calendar, resulting in the observance of Passover before the equinox. Some Christians, especially in the East, followed the new Jewish determination of Passover, while others rejected the Jewish calendrical innovation and made their own independent determination of the Paschal full moon. (Local variations in calendrical practice among both Christians and Jews make the picture somewhat more complicated than I have described here.)

The Council of Nicea, in response to Constantine's request, addressed the issue of when to celebrate Easter. The council decided that Easter should be observed by all Christians on the Sunday following the full moon on or after the vernal equinox. That is really all the Church said about the date of Easter at the time. If you read much about this issue, you will no doubt encounter various claims that the Council of Nicea mandated more detailed formulae for determining the date of Easter (e.g., basing it on the Julian calendar or employing a 19-year lunar cycle), which just happen to coincide with the writer's biases. But such claims are entirely unfounded. Variant lunar cycles, for instance, persisted until the 9th century in some places.

A few decades later, with some Eastern Christians still taking their cue from the Jewish observance of Passover, the Church again addressed the matter in an appendix to the Apostolic Constitutions. Canon VII of the Holy Apostles states, "If any bishop, priest, or deacon celebrates the holy day of Pascha before the vernal equinox with the Jews, let him be deposed." The key phrase here is not "with the Jews," but, rather, "before the vernal equinox." The implication is that Christians are to ignore the new Jewish calendar. The Church had little choice but to make this ruling. The contrary ruling would, essentially, have given the Jews the power to determine when Christians celebrated their most important festival. Here the Church proved more conservative than the rabbinical Jews, retaining the ancient Jewish practice long after the Jews had abandoned it.

The Jews have not observed Passover before the vernal equinox since the 9th century. Their rule-based calendar has drifted, so that now they sometimes observe Passover later than the astronomically determined date, but never earlier. Like this year, for instance. The vernal equinox took place on 20 March, and the moon was full on the following day, 21 March. But the Jews will commence their celebration of Passover at the next full moon, 20 April.

Many Orthodox Christians, perhaps including most of the clergy, seem to believe that the reason we Orthodox Christians observe Easter so late is because the canons require us to observe Easter after the Jews have observed Passover. This year, for instance, Orthodox Easter falls on 27 April, a week after Passover, which is consistent with this claim. But while this might be a useful rule of thumb, it is not an actual rule, let alone a canon. The Passover date that Easter must not precede is that determined by the ancient method – 21 March this year. Far from requiring Christians to celebrate Easter after the new Jewish Passover date, Canon VII of the Holy Apostles actually requires us to ignore the innovative Jewish dating of Passover.

It is easy to demonstrate that the Church has no rule requiring Easter to follow Passover. A number of times in the 6th through 8th centuries, the Church actually celebrated Easter on the same day when the Jews were beginning their celebration of Passover. This last occurred in AD 783. It has not happened since then because the Julian calendar, which came to be used by Christians, drifted even faster than the Jewish calendar. Orthodox Christians still use the Julian calendar for determining the date of Easter. That is the real reason why Orthodox Easter always follows Passover.

It is common knowledge that the Julian calendar currently runs 13 days behind the Gregorian calendar. (Most European Catholic countries and their colonies adopted the Gregorian calendar in 1582, as decreed by Pope Gregory XIII. Other countries were slower. Britain, for example, did not adopt the new calendar until 1752. Greece was the last European country to adopt the Gregorian calendar, in 1923.) What is less well known is that the Orthodox also follow a different calculation of lunar cycle, which runs a few days behind both astronomical reality and the Gregorian lunar cycle. This year, for instance, the astronomical full moon will occur on 20 April, while the Orthodox lunar tables assign the Paschal full moon to 25 April.

The difference, then, between Orthodox and Western Easter dates occurs because 1) the Julian solstice occurs 13 days after the Gregorian solstice, and 2) the Julian full moon occurs 3 to 5 days after the Gregorian full moon. (Both calendars use virtual solstices and full moons based on computation, rather than on actual astronomical observation. In practice, the Gregorian computations are usually closer to physical reality.) By my calculations, based on these two facts, Orthodox Easter should coincide with Western Easter about 20% of the time; it should fall one week later 50% of the time; it should fall four weeks later 10% of the time; and it should fall five weeks later 20% of the time. I think that is pretty close to the actual pattern of variation in recent history.

The Julian calendar, however, continues to drift away from physical reality. After the present century, the two Easters will never again occur four weeks apart. Beginning in 2437, they will sometimes come six weeks apart. And after 2698, the two Easters will never again coincide.

I have referred numerous times to the "rule-based" reformed Jewish calendar. Lest I give an incorrect impression, let me reiterate that, since at least the 5th century, Christians have also used rule-based calendars. Currently, no church determines the date of Easter through direct astronomical observation. In the early first millennium, when these calculated calendars were being devised, communication was not what it is today. Determining the date of Easter by rules, rather than by astronomical observation, was the most practical way to ensure that all Christians celebrated Easter together. But it also embodied a bit of humanistic hubris – a pride in the growing power of human reason to model the mechanics of the universe through its own ingenuity, without further reference to God's physical creation. It would seem to me that a religion based on the Incarnation should hesitate to separate itself from physical reality.

And, indeed, the men who devised the Church's calendar had no such intention; rather, they intended for their calculations to anticipate the physical reality that would eventually obtain. In reforming the Roman calendar, Julius Caesar had been attempting to implement a calendar that would conform to astronomical reality. While the Julian calendar was a vast improvement over its predecessor, it did not quite succeed in matching the movements of the heavens over the long term. The Fathers who argued for various lunar cycles (e.g., 19-year, 84-year, 532-year) did so on the basis of how closely they would conform to reality. If they were here today to see the outcome of their work, I'm sure they would want to have another go at it, to see if they could improve their methods.

And what of those who insist that the Church must retain the Julian calendar? I will never be persuaded that the measurement errors of a pagan Roman emperor constitute an irreformable element of Holy Tradition.

In the centuries following the Council of Nicea, the Church converged on a consensus of using the Julian calendar with a 19-year lunar cycle. Its leaders saw this method as the best way to implement the decision of Nicene Fathers regarding the date of Easter, given the options available at the time. And it worked pretty well for a while. Now it is not working so well, and we see that rigid adherence to these unadjusted formulae results in a growing divergence from the ruling of Nicea.

Together with the Orthodox Theological Society in America, I support the Aleppo Agreement, under which churches would abandon their virtual calendars and extrapolations, and instead base the date of Easter on actual astronomical observation. The OTSA clearly states the Orthodox rationale for Aleppo: "We endorse this proposal on the basis that it reflects most faithfully the norms for calculating the date of Pascha as set out by the Holy Fathers of the First Ecumenical Council." You can't get more Orthodox than that.

For those who want to know more, here are some suggestions for further reading:

Archbishop Peter:
Concerning the Date of Pascha and the 1st Ecumenical Council

Wikipedia: Computus

This Easter/Passover Calculator allows you to plug in a year, and it gives you the dates of Julian Easter, Gregorian Easter, and Passover.

I decided to add a list of actual dates for 2008, which might clarify things for those who think concretely, rather than abstractly.

Ancient Jewish (Astronomical) Calendar
7 March – New Moon / New Year / 1 Nisan
20 March – Vernal Equinox
21 March – Full Moon / Passover / 15 Nisan

Reformed Jewish Calendar
Year 5768 – 11th year of 19-year cycle
6 April – New Moon / 1 Nisan
20 April – Full Moon / Passover / 15 Nisan

Julian Calendar (with Gregorian dates)
3 April – Vernal Equinox
25 April – Paschal Full Moon
27 April – Easter / Pascha

Gregorian Calendar
14th year of 19-year cycle
21 March – Vernal Equinox
22 March – Paschal Full Moon
23 March – Easter

1 comment:

Sara K. said...

So interesting and kind of unfathomable for me! -S