OK, LJ Brain Trust

[rhu]

A quick Google and Wikipedia search has been unable to locate a satisfactory answer to this question:

Both Passover and Easter are scheduled based on the 19-year Metonic cycle. In some years, such as this one, however, Judaism intercalates the extra month one year before the Western Church does, resulting in Easter and Passover not coinciding. What is the nature of the difference in calculation, when was that difference introduced, and why?

Comments

[saxikath]

I have a vague memory, from something I read sometime in grad school maybe, that certain branches of the Christian church actively wanted to avoid having Easter coincide with Passover. (Yes, this makes no sense from a historical point of view.) I believe this also ties in with why the Eastern and Western churches calculate Easter differently (if you notice, Orthodox Easter comes much closer to Passover this year than Western Easter); the Western church wanted to avoid coinciding and the Eastern church stuck with the original calculations.

This is all a patchy memory, so I may not have the details right, but I do think there was some aspect of this involved.

[kirisutogomen.livejournal.com]

You mentioned a quick Google search, but did you run across the article on Computus? I don't have the patience to read it closely, but it seems like you ought to be able to figure out what the heck they're doing.

[530nm330hz.livejournal.com]

Ah, a cursory glance offers a probable explanation: The Jewish calendar knows nothing about the Gregorian calendar, so when the full moon comes close after the equinox (as this year) perhaps the Jewish calendrical computation mistakenly treats it as before the equinox.

[530nm330hz.livejournal.com]

Ah, and in fact that helped me refine my Googling and I found this (emphasis added):

If you pay attention to the dates of Easter and Passover from year to year, you will notice that although they usually fall within a week or so of each other, on occasion Passover falls about a month after (Gregorian) Easter. At the present time, this happens in in the 3rd, 11th, and 14th years of the Metonoic Cycle (i.e., when the Golden Number equals 3, 11, or 14). The reason for this discrepancy is the fact that although the Metonic Cycle is very good, it is not perfect (as we've seen in this course). In particular, it is a little off if you use it to predict the length of the tropical year. So, over the centuries the date of the vernal equinox, as predicted by the Metonic Cycle, has been drifting to later and later dates. So, the rule for Passover, which was originally intended to track the vernal equinox, has gotten a few days off. In ancient times this was never a problem since Passover was set by actual observations of the Moon and of the vernal equinox. However, after Hillel II standardized the Hebrew calendar in the 4th century, actual observations of celestial events no longer played a part in the determination of the date of Passover. The Gregorian calendar reform of 1582 brought the Western Church back into conformity with astronomical events, hence the discrepancy.

So that explains why, when, and by whom.

[autotruezone.livejournal.com]

Sure there's been some drift, but I'm not sure that's the whole story. IIRC, not only Pesach, but the beginning of the month of Nisan, has to be after the equinox (remember, it's supposed to be the month of Spring). If we hadn't had a Jewish leap year this year, the equinox wouldn't have come until nearly two weeks into Nisan, just before Passover itself). The rule for Easter only seems to require that the holiday itself be in spring, not the lunar month in which it occurs.

[autotruezone.livejournal.com]

No, scratch that -- that's obviously not the case, given that Passover sometimes does come in March. But I'm going to look into this a bit more anyway.