For some reason, I thought the Easter holiday always coincided with Passover. I know how the date for Easter is calculated- the first Sunday after the first full moon after the spring equinox (right?). I thought this was based on how Jews calculated the date for Passover. I’m pretty sure last time I paid attention Passover occurred during Holy Week. So what’s up this year? How is the date for Passover actually calculated?
The Jewish calendar is a lunar calendar. As such it doesn’t quite match up with the solar year. The variance is enough that it gets, at certain times, a whole leap month. This is one of those years.
Western Christians don’t change their method of calculating the day of Easter, so this is the reason for the gap this year. But Orthodox Christian do take into account the date of Passover, so as to have Easter coincide with it. Orthodox Easter, this year, is on April 27.
This site also has some good info.
OK, the simple form: Easter is the first Sunday following the first full moon after the vernal equinox. Passover is based on a lunar calendar, where the months begin on the new moon, and starts on the 14th day of the “spring month.” So, Passover starts on the full moon and runs for 8 days (or 7 days in Israel) and thus Easter usually falls on the Sunday during Passover.
However, because the Jewish calendar is based on the lunar year, it loses around 11 days each year against the solar year. [sup]*[/sup] The Jewish holidays were originally harvest-related, so need to come out seasonally; the calendar must therefore be adjusted so that it doesn’t lag the solar year. Thus, a full month is added seven times every 19 years. So, in a Jewish “leap year” the spring month starts well after the equinox. In such a year, and especially when the full moon comes immediately after the spring equinox, then Passover comes out almost a month after Easter… or, if you prefer, Easter comes out almost a month before Passover.
This is not a “rare” occurrence, in the sense that it happens every eight or ten years or so (I’m guessing, I haven’t looked it up.)
That help?
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- Aside: the Muslim calendar does the same, but doesn’t adjust, and so holidays do not come out seasonally each year.
From what I’ve gathered from a bit of research online, it usually happens three times in every nineteen-year cycle of the Hebrew calendar, at the ends of years 8, 11, and 19 of the Metonic cycle. Currently we’re nearing the end of year 11 in the cycle (note that the leap months are inserted at the end of year in the Hebrew calendar.) So the last time this happened was in the Gregorian year 2005, and the time before that was 1997. Next time it’ll happen will be in Gregorian year 2016, and after that 2024.
orthodox pascha is calculated on julian and can not be celebrated before passover.
passover and pascha are only 1 week apart.
Eastern Orthodox Easter always does, Catholic/Protestant Easter sometimes but not always does.
No. The solstices don’t really play an explicit role in the Jewish calendar like they do in the calculation of Western Easter. That rule was intended to make Easter come out to be around the right time of year for Passover, but to make the Western Christian calendar independent of the Jewish calendar.
I think that may be beyond human comprehension. There’s certainly no easy rule like “the first Sunday after the first full moon after the spring equinox” (nitpick: actually March 21, not the actual vernal equinox).
In practice, these days, we Google it 
I also have a book at home that has the Jewish calendar calculated from 1900 to 2100.
The Jewish calendar is lunisolar, months synch to lunations while years – over the course of the 19 year Metonic cycle – synch to solar years. (The Metonic cycle is 7 13-month years in a 19 year cycle.) Passover is the 15th day of the first month (with days starting around civil twilight), and thus coincides with the first full moon after the equinox. But as Dex noted, this year the equinox happened right under the full moon and during the intercalation month, so Passover falls 30 days after the equinox this year.
So after all of the above excellent explanations, just to make things very clear, the date for Passover is always the same (the 15th of the month of Nisan), and is not calculated in any way. It’s just that the Jewish calendar and the Western one are different calendars, organized in different ways.