Monday, March 24, 2008

End of an era

Here in Jerusalem (and theoretically in other cities that were walled at the time of Joshua), we just completed Purim Meshulash, a 3-day Purim celebration (Friday-Saturday-Sunday) that occurs any time the date of Purim falls on Shabbat. Since 14 Adar never falls on Shabbat but 15 Adar sometimes does, this is only relevant in walled cities (and practically speaking, only in Jerusalem).

We just had another Purim Meshulash 3 years ago, but there won't be another one for another 13 years! Because you see, we're on the cusp of a major transition in the Hebrew calendar.

Some background information: (Licensed calendar geeks can skip right to the data.)

There are three variables that make one Hebrew year different from another:
1) Cheshvan can have 29 or 30 days.
2) Kislev can have 29 or 30 days.
3) There can be one or two months of Adar.

This means that the 9-month period from Adar to Cheshvan (which just happens to include all the biblical holidays plus Purim; forget about Chanukah though) is completely fixed. If you know the day of the week of any holiday in that period, you know them all.

Therefore, since Rosh Hashanah can only fall on four days of the week (Monday, Tuesday, Thursday, Saturday), there are only four types of years if we're just looking at the period from Adar to Cheshvan. (Since this period spans two Hebrew years, I'm using Gregorian year numbers below for clarity.)

The four types, in order of frequency, with their distinctive features:
  • Rosh Hashanah on Thursday, 31.9% of years. This means there is a "three-day yom tov" for Rosh Hashanah, and for those who observe 2 days of yom tov, there are two more "three-day yom tovs" for Sukkot and Shemini Atzeret. Yom Kippur is on Shabbat. Purim begins on Saturday night. We just had this in 2007.
  • Rosh Hashanah on Shabbat, 28.6% of years. Most of the fall holidays are on weekends. Pesach starts on a Wednesday night, leading to a "three-day yom tov" for those who observe 2 days of yom tov. Shavuot is on Friday, leading into (or including) Shabbat. This causes a disparity between 1-day-yom-tov and 2-day-yom-tov communities regarding Torah reading for several Shabbatot.
  • Rosh Hashanah on Monday, 28.0% of years. Pesach begins on Shabbat. This also causes a disparity regarding Torah reading, because the 8th day of Pesach (if one exists) is also on Shabbat. Shavuot begins on Saturday night, yet another "three-day yom tov" for people who swing that way. Tisha B'Av falls on Shabbat and is delayed to Sunday.
  • Rosh Hashanah on Tuesday, the least common by far with only 11.5% of years. This is what we have in 2008. Pesach begins on Saturday night, leading to all manner of hijinks. Tisha B'Av also begins on Saturday night. Purim is on Friday, leading to Purim Meshulash in walled cities.
You may notice, thinking about recent years, that some of these descriptions sound more familiar than others, and that this doesn't necessarily match their statistical frequency. That's because, as recent and upcoming years demonstrate, the year patterns are NOT AT ALL distributed homogeneously.

Let's look at the days of the week of Rosh Hashanah in recent years (and next year):

1996 Sat
1997 Thu
1998 Mon
1999 Sat
2000 Sat
2001 Tues
2002 Sat
2003 Sat
2004 Thu
2005 Tues
2006 Sat
2007 Thu
2008 Tues
2009 Sat

So what do we have here? A lot of Saturdays (50% of the years in this sample, including 4 years out of 5 for one 5-year span there), more Tuesdays than would be statistically expected (you'd expect about one a decade), and no Mondays at all for over a decade.

But that's about to change drastically:

2010 Thu
2011 Thu
2012 Mon
2013 Thu
2014 Thu
2015 Mon
2016 Mon
2017 Thu
2018 Mon
2019 Mon

Yes, that's right -- the entire decade of the 2010s will be nothing but Thursdays and Mondays! The convenience to working people of having the fall holidays on weekends, which we have grown accustomed to, will be wholly alien for the new generation. Mechon Hadar's new page about Purim on Friday will be a purely academic exercise, as will all the guides to Shabbat Erev Pesach that will see a lot of use this year.

After that, things will start to stabilize:

2020 Sat
2021 Tues
2022 Mon
2023 Sat
2024 Thu
2025 Tues
2026 Sat
2027 Sat
2028 Thu
2029 Mon

So that's the long-term forecast!

22 comments:

  1. Assuming 2 day yom tov observance here are the total number of weekday holidays for each alignment in a secular calendar year.

    RH Mon: 9
    RH Tue: 10
    RH Thur: 12
    RH Sat: 6

    Note that Good Friday might fall on Pesach and Columbus day might fall on RH/SK in the Monday alignment which could reduce the total workdays missed. But in general, it's a good time to start working for a Jewish organization.

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  2. And the numbers for 1-day yom tov:

    RH Mon: 6
    RH Tue: 6
    RH Thu: 8
    RH Sat: 4

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  3. Let me tell you, it was so nice for that 5 year stretch of 4 holiday-on-the-weekend years to fall during my 4 years of college and first year in the working world. I really feel for current and future college students; it's gotta be so much harder.

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  4. Yeah. For me it was my last 2 years of college and first 2 years in the American working world, and the non-Shabbat year in between was when I lived in Israel so it didn't matter.

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  5. Note that Good Friday might fall on Pesach and Columbus day might fall on RH/SK in the Monday alignment which could reduce the total workdays missed.

    Also Shavuot can fall on Memorial Day (as it did in 2001).

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  6. I guess it depends on what type of classes you take, but I hated RH falling on weekends in college. Losing every weekend for a month made it much harder to keep up with my work than missing classes during the week.

    I wonder whether the Monday alignment could have Good Friday, Columbus day, and Memorial day all fall on yom tov? What is the lowest possible number of yom tov days on work days taking into account all US holidays?

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  7. I remember that everything fell on weekends or US holidays in 5761 (2000-01): Rosh Hashanah, Sukkot, and Shemini Atzeret were on weekends, Yom Kippur was on Columbus Day, the 1st day of Pesach was Sunday and the 7th day was Saturday, and Shavuot was on Memorial Day. (2-day-yom tov people still had to take off the 2nd days of Pesach and Shavuot.) But I guess if we're talking about Hebrew years now, we're changing the rules of the game.

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  8. A related question: Is there a variable in the number of aliyot to the Torah in a given year? Is more time spent at keriat ha-torah in some years than in others?

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  9. On the other hand, in terms of the work-week, RH Thurs is less disruptive than RH Mon, and both are MUCH less disruptive than RH Tues, which breaks the work-week up into unproductive chunks of a day or two for nearly a month.

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  10. Anonymous: Yes. Time spent during kriyat hatorah first: For example, on leap years, you obviously don't read more total torah on Shabbat mornings, but you read more on Monday/Thursday/Mincha. Also, if the 8th day of Pesach or the 2nd day of Shavuot falls on Shabbat, the reading is longer than it would be on a weekday (and those might not be the only two examples).

    As for number of aliyot, it can vary even more. Aside from the same leap year situation above, you have yom tovs adding 0 aliyot to the usual if they fall on Shabbat, 2 if they fall on Monday or Thursday, and 5 if they fall on any other day. And, to take a particularly subtle situation, 3 weeks ago for Shabbat Shekalim Rosh Chodesh Adar, some communities had 8 aliyot plus maftir, when normally neither Shekalim nor Shabbat Rosh Chodesh would cause the number of aliyot to change. (Some communities just combined shishi and sh'vii to avoid that situation.)

    And I'm probably forgetting something even more obvious...

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  11. Great post, BZ! Very clearly explained. There's a mnemonic that should be mentioned here, but I forget it... :) Oh, yeah:

    Think of AT-BaSh, the code of matching the first letter of the alphabet with the last letter, etc. The first day of Pesach (Aleph) falls on the same day of the week as Tisha B'Av (Taf). The second day of Pesach (Bet) falls on the the same day of the week as Shavuot (Shin). 3rd day of Pesach - Rosh Hashanah. It keeps going like that, all the way through to (the way I learned it) 7th day - Yom HaAtzmaut.

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  12. Where do the percentages come from? Is this on a continuous loop similar to the solar-lunar calendar 19 year loop?

    I am really looking forward to having vacation time in 2000. I was so sad to learn today that this will not be happening again in the near future.

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  13. Where do the percentages come from? Is this on a continuous loop similar to the solar-lunar calendar 19 year loop?

    Yes, except this loop is 689472 years long. I kid you not. See the full stats.

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  14. Another major factor for number of aliyot (without affecting the amount of Torah read, beyond the length of the maftir) is that each double parasha has 7 aliyot when they are read together, and 14 aliyot when they are read separately.

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  15. On the other hand, in terms of the work-week, RH Thurs is less disruptive than RH Mon

    In Israel (where Monday is in the middle of the work week), perhaps. But in the US, having erev chag on Sunday facilitates travel.

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  16. How did R Hillel (or whoever) figure this stuff out, without Excel (which by the way contains less rows than years in the loop)?

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  17. dl: I'm sure he just wrote a perl script.

    Actually, in reality, the math to figure out one year from the previous year isn't hard, using a little modular arithmetic that Rambam details in hilchot kiddush hachodesh. It's when you try to generalize and figure out exact percentages and stuff that it gets a bit more annoying, but doing so is also unnecessary.

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  18. --
    In Israel (where Monday is in the middle of the work week), perhaps. But in the US, having erev chag on Sunday facilitates travel.
    --

    That part is a wash- if you're traveling you presumably need to travel back, and having motzai yom tom on a Shabbat or Sunday facilites traveling back.
    I was assuming that Mondays are more productive/valuable days to be working than Fridays in general, but that might not be generally the case. In any acse the difference is marginal. By far the most disruptive is RH Tuesday.

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  19. Traveling back on motza'ei yom tov (on any day of the week) is doable, but traveling on a weekday erev yom tov without missing part or all of a work day is difficult to impossible (depending on the distance traveled and the time of sundown).

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  20. Traveling back can also be problematic. Try finding a flight after Shavuot. Havdalah is 9:09pm in New York, factor in travel time to the airport and security and you're talking about 10:30pm at the earliest. If you're not on a major route forget about getting a flight before the next morning. And then who knows what time that flight gets back to your home city. Time zones can make the problem even worse if you're traveling east.

    Traveling is disruptive in general, but there are too many variables between locations and modes of transportations to generalize best/worst cases. Also depending on personal responsibilities leaving early can sometimes be easier/preferable to arriving late.

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  21. Mechon Hadar's new page about Purim on Friday will be a purely academic exercise, as will all the guides to Shabbat Erev Pesach that will see a lot of use this year.

    Meanwhile, Hoshanah Rabbah will enjoy a resurgence of interest, due to all the years that it will fall on Sunday, making it accessible to working people.

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