I have a 2002 calendar and wonder if I will ever be able to use it again. Things to consider are dates, moon cycles, holidays that move (Easter, Passover etc.), first day of seasons. Will I ever be able to use this calendar again? How about my descendants if I pass it on?

To keep things in perspective, let’s only consider major Christian, Jewish, and Muslim holidays and US Federal holidays.

The lunar calendar is 11 days shorter than the solar calendar so the next time the two coincide will be in about 33 years. But then will the days of the week align? They should align sometime within 231 years. You would have to find the years the moon cycles are the same and then check to make sure the days of the week were also right. Good luck!

It probably will but you might be waiting for a while, at least ten years.

There are fourteen different possibilities to get the days of the week right (seven + seven for leap years). 2002 started on a Tuesday. The next year that will start on a Tuesday is 2008 (but that is a leap year). The next non-leap year starting on a Tuesday is 2013.

As for moveable feasts, I think most of them are lunar based and so my WAG is that there are 56 different possibilities depending on which phase the moon is in when each year starts + leap years. I’m not sure how Islamic and Jewish festivals are calculated, but Easter is pretty complex, something to do with the first full moon after the Equinox.

I’m not sure what phase the moon was in on 1 January 2002, so I’ve no idea whether 2013 will match up. If it doesn’t it could be a long wait.

Easter was on 3/31. That will only repeat in 2013, 2024, 2086 and 2097, which is as far as the calendar I found would go.

Jan 1st, 2002 was a Tuesday. That is also true in 2013, 2086, and 2097. None of those was a leap year either. Does eliminate 2024 though.

2002 Lunar cycle was full moons on 1/28, 2/27, 3/28, 4/27, 5/26, 6/24, etc. 2013 is 1/27, 2/25, etc… 2086 is 1/29, 2/28, etc. 2097 is 1/27, 2/26 etc. So no matches.

So no good for the next century.

Most holidays would not be a problem (July 4, Thanksgiving, Halloween, etc.) because they are tied to a specific date or certain day (like the last Monday of the month, or something).

Holidays like Easter (and therefore Ash Wednesday, Palm Sunday, Good Friday) are tied to the lunar calendar, so if you can find a year when the days of the week line up w/ the lunar calendar as **AcidKid** points out, they should line up. Can’t speak for the determination of Jewish/Muslim holidays, though.

If you can find a list of future Easter dates (there is one in the Anglican Book of Common Prayer, but it is probably not long enough for you) you can eliminate any year that doesn’t have the same Easter date as 2002 did. All of the lunar cycles for those years should be within a week of each other, so you would then have to narrow it down further.

If you’re just interested in dates and days of the week (which will get you most Christian and all secular American holidays), then there are only 14 different calendars. All you need to know is the day of the week the year starts on, and whether it’s a leap year. But you mentioned moon cycles as well. Roughly, there are 28 different phases that the Moon could be in on January 1, so that would put the number of different calendars at 392. Even there, there might not be a perfect match, since the length of the lunar cycle isn’t exactly 28 days. So two calendars might start off with full moons falling on the same dates, but end up with them on different dates, due to accumulated roundoff error.

If you did manage to get the moons right, that would get you Easter and the holidays connected to it (Ash Wednesday, Pentecost, etc.), and I think the Jewish holidays as well, since the Jewish lunar calendar has corrections built in to keep it in step with the solar year. The Muslim calendar, however, is pure lunar, which brings in added complications. Even if the full moon falls on the same date in two different years, it might be the first full moon of one Islamic year, but the second full moon of the other year (or any other combination). So even if the weekday, lunar phase, and solar year all line up, you’ve still only got a 1 in 12 chance of matching the Islamic dates. So there’s overall only a 1 in 4704 chance of two randomly selected years matching to the standards you requested. This is not to say, necessarily, that the next match for this year will be 4704 years from now: It might be longer or shorter than that. But I’m not going to be the one to calculate it.

**SmackFu** beat me to it.

The lunar calendar is a 19 year cycle, right? So that should mean that, worst case, the calendar will match up every 4 * 7 * 19 = 532 years. This page has a method for calculating Easter. By that algorithm, the next year after 2002 that has the same Easter date and is 2002 plus some multiple of 532 is 9450.

So, a long way off.

“Sure, it’s not 1985 now, but who knows what tomorrow could bring?”-Homer Simpson

In 1982 I bought a copy of John Lennon’s ‘Imagine’. I somehow managed to get an LP from the original release in 1971, which included a calendar for that year.

It also aligned with 1982, which I found a bit eerie.

Actually, it’s even a little bit worse than that. The above is just for Christian, Jewish, and Federal holidays. But you wanted Islamic holidays, too. Unfortunately, the Islamic calendar is not tied to the solar year at all, and precesses around it.

I remember in the old yellow pages, in the back was a page or 2 full of calendars numbered 1 through 20 or something and then there was a list of years with the coresponding calendar number.

The lunar cycle *approximately* repeats every 19 years, but not exactly. If it were exact, then any multiple of 532 would give you the same Easter.

Besides which, 532 is more than enough to run you into the century exception to leap years, which will throw your cycle off every time it happens.