11 ms·

Jewish Calendar Demystified (2007)

136 points by nvr219 4y ago

otterley 4y ago
(2007)
- aaronbrethorst 4y ago
  (5767 or 5768)
  - chabad360 4y ago
    Hmm, considering that the Jewish New Year ended in the middle of September that year, it actually is a question. I suppose it depends on whether that journal was actually published before or after Rosh Hashanah that year.
- dang 4y ago
  Added above. Thanks!
  - deleted 4y ago
    [deleted]
verbify 4y ago
I was born on the 30th of Cheshvan which as he explains is one of the days that doesn't show up every year (I guess is the equivalent of February 29th). I've always wondered how many birthdays I've had - does anyone know of a list of which years are chasar/maalei? The missing years are also interesting: https://en.m.wikipedia.org/wiki/Missing_years_(Jewish_calendar) https://en.m.wikipedia.org/wiki/Missing_years_(Jewish_calend...
- Fatnino 4y ago
  I was born right at sunset between the 29th of Cheshvan and the 1st of Kislev. It's like I was trying to be born on the 30th. It's not actually totally clear when my birthday is but I generally use 1st of Kislev. Fun fact, the year of my Bar Mitzvah there was a 30th of Cheshvan so it was something like "I turn 13 on Tuesday or Thursday, but definitely not Wednesday".
dotancohen 4y ago
The relation to the bug in his code at the end was interesting. It took the story in a direction that I was not expecting. Honestly, reading through the first 95% of the fine article I was wondering why this was posted to HN. The end was worth it.
- lupire 4y ago
  The bug was foreshadowed in the beginning of the story when he said that the first year was the same as the first week. Steve Morse should have asked Rabbi/Professor/Mathematician/Cosmologist Shlomo Sternberg, Mathematician/Cosmologist (Born 1936), for help in the 1970s or 1980s. He also proved swordfish is kosher. https://en.m.wikipedia.org/wiki/Shlomo_Sternberg https://en.m.wikipedia.org/wiki/Shlomo_Sternberg
h4n1 4y ago
The 19-year metonic cycle (of the Jewish and Chinese calendars) has always struck me as clever but inconvenient - how do you quickly calculate if we'll have an extra month in x years from now? The Gregorian calendar's algorithm - every 4 years, except if divisible by 100, except if also divisible by 400 - is both clever and elegant.
- lupire 4y ago
  All you have to do is learn astronomy. It's more civilized. Lunar calendar = more technologically advanced society.
  - adastra22 4y ago
    Why should our time keeping on Earth have anything to do with the moon?
    - krapp 4y ago
      Because the moon is a big bright ball in the sky which regularly moves through predictable, easily observable phases, making it an obvious basis for a system of measuring time.
      - schoen 4y ago
        The complexities, irregularities, and imprecisions of our calendars are due to things like * the Earth's rotational period ("day") * the Moon's orbital period ("month") * the Earth's orbital period ("year") not being integer multiples of each other at all! Despite that, we naturally want to keep time in terms of each of these -- as you said, they're all such extremely noticeable periodic phenomena. According to GNU units, the day is 24 hr = 86400 s (which is a historical basis for defining the second, though not the method we officially use now because we have clocks that are more consistent than the Earth's rotation), while the lunar month is 29 days + 12 hours + 44 minutes + 2.8 seconds = 2551442.8 s and the tropical year is 365.242198781 day = 31556926 s If we think of a month as a fixed whole number of days, and/or think of a year as a fixed whole number of months, and/or think of a year as fixed whole number of days, it's been known for thousands of years that we're eventually going to get in trouble astronomically and require some adjustments.
LastTrain 4y ago
Nothing demystifies a subject like putting it into quasi-biblical verse.
zokier 4y ago
Its curious that with the all day additions and removals it still doesn't correct more accurately to the drift. 1 day for 217 years might not be huge, but still feels significant, especially when considering that the julian calendars 1 day per 128 years was deemed unacceptable already back in 16th century. Although I suppose correcting might be tricky without compromising on the lunar cycle accuracy?
- wbl 4y ago
  There is no Sanhedrin, the only body that could correct this without a schism. As for making the correction a slight mucking about with the molead rules could do it.
  - tkk23 4y ago
    There is also the internet. Maybe everybody agrees and there is no objection to a correction? It could be as easy as creating a Mastodon instance to find out.
  - jaza 4y ago
    Pan-Jewish changes to Halakha (orthodox law) are still theoretically possible. The last significant such occurrence was the ban on polygamy in Judaism about a millennium ago. It's just a question of how many rabbis, across how many streams of Judaism, would need to reach a consensus, in order for it to be reasonable to consider an amendment as "widely accepted". In terms of changing the calendar rules, I doubt that there would be any chance of pan-Jewish consensus for quite a few more millennia, that is, not until the dates of major festivals get significantly more out of whack than they are now.
    - compsciphd 4y ago
      hey, some (major) rabbis believe that sabbath in japan should be on sunday. (and others believe that in western alaskan islands, it be friday, i.e. if there's a concept of a "date line" in halacha, than the area between the international date line and the halacha date line would be offset by a day depending on which side it is).
connorgutman 4y ago
This Rosh Hashanah I switched to the Jewish calendar full-time. I know this may sound impractical (it is) but it has always felt like an important issue to me as a mostly secular Jewish American. In my opinion the Gregorian calendar offers very little advantage (perhaps even disadvantage) over lunar-solar alternatives. Its popularity has been deeply tied to Christian imperialism and its adoption has often been forced. The Gregorian calendar is technically more accurate as it is off by 27 sec/year (1 day in 3236 years) compared to the Jewish calendar which is off by 7 min/year (1 day in 216 years). This, however, has always felt to me like comparing apples to oranges. The accuracy of the Gregorian calendar comes at the expense of functionality (lunar calculations) which I find to be incredibly useful. With the Jewish calendar you always know what phase the moon is in as the start of each month is a new moon and the middle is a full moon. Not only does this have real-world application in terms of tides, agricultural conditions, night light, animal behaviors, and etc but I have found myself feeling more mindful of nature as a result. It still trips me out that I can go outside and know exactly what the moon is going to look like without googling it! Furthermore, days ending at sundown makes so much more sense to me! There is a certain satisfaction that comes with watching the sunset and it marking the end of your day compared to the day ending in the middle of the night while you are asleep. Lastly, I have felt myself feeling far more connected to my culture as I am more aware of holidays and other traditions that were lost when the Gregorian calendar took over. Some resources for those who are interested: libhdate (Jewish date + cal alternative for Linux) https://sourceforge.net/p/libhdate/wiki/Home/ https://sourceforge.net/p/libhdate/wiki/Home/ hebcal (RSS, CSV, Google/Apple/etc calendar integration) https://www.hebcal.com/ https://www.hebcal.com/ On my android phone I used KLCK and KWGT with the hebcal RSS feed above to create a lockscreen and homescreen Jewish calendar widget. On my laptop I run Sway+Waybar and created a custom waybar module with libhdate. It's not perfect but it's working for now!
- willhinsa 4y ago
  I’m not Jewish, but that sounds really appealing to me!
- js2 4y ago
  You might find this book a hoot. I did: https://ajjacobs.com/books/the-year-of-living-biblically/ https://ajjacobs.com/books/the-year-of-living-biblically/
nimbius 4y ago
I had a Jewish friend who once remarked that he knew when rosh hashana and yom Kippur were upon him because it added another forty minutes to his commute in Los angeles. he affectionately called it "the ten days of 'awe come on merge already'"
- js2 4y ago
  I'm Jewish but I don't get it... am I to take it that Jews going to temple added enough traffic to L.A. to slow down his commute by forty minutes?
  - wbl 4y ago
    Probably being extra polite at the expense of using the road effectively
  - arrosenberg 4y ago
    Yes, adding several hundred drivers all entering/exiting at the same spot in rush hour at specific spots the 405 can do that. Thinking the one on Mulholland Drive right near the 101/405 interchange.
    - thakoppno 4y ago
      Isn’t that where the skirball center is?
  - svat 4y ago
    Tom Lehrer wrote a song called "I'm Spending Hanukkah in Santa Monica" (https://www.youtube.com/watch?v=LslsgH3-UFU https://www.youtube.com/watch?v=LslsgH3-UFU) — I had assumed it was just a joke for the rhyme, but looking at this conversation I'm wondering if there's anything more to it :)
    - antognini 4y ago
      There's something to it, historically LA's Jewish population has been clustered in the West Side.
xwowsersx 4y ago
I highly recommend reading Calendrical Calculations, a book by Edward Reingold and Nachum Dershowitz. It is a beautiful combination of computer science and calendar systems. Also, the Hebrew calendar truly is a marvel, as the book goes through.
dhosek 4y ago
One of the things I love ab out the Hebrew calendar is that the leap month, Veadar is literally “and Adar,” Adar being the month that precedes Veadar.
- xwowsersx 4y ago
  I've never heard that. As far as I know, it's known as Adar aleph (A) and Adar bet (B)
  - schoen 4y ago
    I heard "Adar Rishon" and "Adar Sheni" (written "Adar I" and "Adar II"). I've enjoyed thinking of the latter as like a movie sequel. "Adar II: The Revenge of Adar". Apparently all of these forms are common. https://en.wikipedia.org/wiki/Adar#Names_and_Leap_Years https://en.wikipedia.org/wiki/Adar#Names_and_Leap_Years
    - xwowsersx 4y ago
      Right, that's essentially the same thing, with aleph being a shortened way of saying rishon and bet being a shortened way of saying sheni. My original point was that I'd never heard of "ve'adar". Apparently as the Wikipedia entry says, that's less common. Curious if the Mishna or Talmud ever uses "ve'adar" (I've never seen it, but doesn't mean it doesn't exist)
      - deleted 4y ago
        [deleted]
      - dhosek 4y ago
        I learned it from my Hebrew textbook. The article also uses it, alongside Adar 1 & 2
joelberman 4y ago
It is much easier to calculate eclipses using a lunar calendar. All lunar eclipses happen during a full moon and all solar eclipses during a new moon.
riffic 4y ago
site's author Stephen P. Morse is the architect of the 8086 processor: https://en.wikipedia.org/wiki/Stephen_P._Morse https://en.wikipedia.org/wiki/Stephen_P._Morse
uptownfunk 4y ago
The Jewish are not the only one. In fact the Indian calendars also called panchanga, have a very elaborate system tied to the luni-solar movement and get very detailed into calculation. My guru once jokingly said when he was nominated to lead his specific religious institution, I’ll only agree to head the mission if I Don’t have to deal with the calendar calculation. As there are many parameters which tend to invite debate. Here is one I use almost daily for the Vaishnavite sect I follow. (1) you’ll notice you have to select your time zone and city as some of the holy fast days (also tied to luni-solar movement called ekAdaShi) depend on the sunrise time. Actually this month that we are entering, also known as Kartik, named after the constellation Krttika, where the moon is full, is a very holy month in the Indian calendar and contains the special Diwali festival on the amavasya or new moon night. (1) https://www.purebhakti.com/resources/vaisnava-calendar https://www.purebhakti.com/resources/vaisnava-calendar
- dotancohen 4y ago
  The full moon falls into a different constellation roughly every month, no?
uptownfunk 4y ago
Would be an interesting paper to compare calendars worldwide. I am seeing many parallels between the Jewish and Hindu calendars. Ours also has an extra month thrown in every few years which is called Adhik Maas, mal maas, or purushottam. This article is quite well written and also entertaining at the same time. I enjoyed it
zx10rse 4y ago
For anyone interested in calendars, check the proto-Bulgarian calendar. It is considered to be one of the oldest if not the oldest, and most accurate in the world by UNESCO. There is a website that rebuild it from the ancient documents describing it, and it is compared head to head with the Gregorian calendar, you can also find the code on github, it is cool. According to it we live in year 7527-th :) Link to the calendar - https://bgkalendar.com/index.php?lang=en https://bgkalendar.com/index.php?lang=en
ossusermivami 4y ago
I remember a long time reading a text file from a package while browsing my /usr/share/docs about the history of Gregorian calendar date in the history, i think it was pretty interesting but I can't find the name of that package of where this was located, (can't seem to be in coreutils/utils-linux except if that has been removed). if anyone would know what i am talking about, i'll be grateful to know the name of the package.
nanna 4y ago
Emacs supports the Hebrew calendar out of the box (alongside Julian, Islamic, Chinese, Mayan, Coptic, French Revolutionary etc etc) but I've never worked out how make much use of it. Anyone have suggestions to get the festivals into Org Agenda, for example?
jaza 4y ago
While in synagogue on Yom Kippur a few days ago, I noticed (for the first time) that the "song of the day" in the Machzor (prayer book just for Yom Kippur) only has options for Monday, Wednesday, Thursday, and Saturday. And it made me think, how can they be so sure that Yom Kippur will never fall on a Sunday, Tuesday, or Friday? Thanks to this wonderful write-up, now I know: the Jewish calendar has a "business rule" that guarantees it!

136 points by nvr219 4y ago

otterley 4y ago

(2007)

aaronbrethorst 4y ago
(5767 or 5768)
- chabad360 4y ago
  Hmm, considering that the Jewish New Year ended in the middle of September that year, it actually is a question. I suppose it depends on whether that journal was actually published before or after Rosh Hashanah that year.
dang 4y ago
Added above. Thanks!
- deleted 4y ago
  [deleted]

verbify 4y ago

I was born on the 30th of Cheshvan which as he explains is one of the days that doesn't show up every year (I guess is the equivalent of February 29th). I've always wondered how many birthdays I've had - does anyone know of a list of which years are chasar/maalei? The missing years are also interesting: https://en.m.wikipedia.org/wiki/Missing_years_(Jewish_calendar) https://en.m.wikipedia.org/wiki/Missing_years_(Jewish_calend...

Fatnino 4y ago
I was born right at sunset between the 29th of Cheshvan and the 1st of Kislev. It's like I was trying to be born on the 30th. It's not actually totally clear when my birthday is but I generally use 1st of Kislev. Fun fact, the year of my Bar Mitzvah there was a 30th of Cheshvan so it was something like "I turn 13 on Tuesday or Thursday, but definitely not Wednesday".

dotancohen 4y ago

The relation to the bug in his code at the end was interesting. It took the story in a direction that I was not expecting. Honestly, reading through the first 95% of the fine article I was wondering why this was posted to HN. The end was worth it.

lupire 4y ago
The bug was foreshadowed in the beginning of the story when he said that the first year was the same as the first week. Steve Morse should have asked Rabbi/Professor/Mathematician/Cosmologist Shlomo Sternberg, Mathematician/Cosmologist (Born 1936), for help in the 1970s or 1980s. He also proved swordfish is kosher. https://en.m.wikipedia.org/wiki/Shlomo_Sternberg https://en.m.wikipedia.org/wiki/Shlomo_Sternberg

h4n1 4y ago

The 19-year metonic cycle (of the Jewish and Chinese calendars) has always struck me as clever but inconvenient - how do you quickly calculate if we'll have an extra month in x years from now? The Gregorian calendar's algorithm - every 4 years, except if divisible by 100, except if also divisible by 400 - is both clever and elegant.

lupire 4y ago
All you have to do is learn astronomy. It's more civilized. Lunar calendar = more technologically advanced society.
- adastra22 4y ago
  Why should our time keeping on Earth have anything to do with the moon?
  - krapp 4y ago
    Because the moon is a big bright ball in the sky which regularly moves through predictable, easily observable phases, making it an obvious basis for a system of measuring time.
    - schoen 4y ago
      The complexities, irregularities, and imprecisions of our calendars are due to things like * the Earth's rotational period ("day") * the Moon's orbital period ("month") * the Earth's orbital period ("year") not being integer multiples of each other at all! Despite that, we naturally want to keep time in terms of each of these -- as you said, they're all such extremely noticeable periodic phenomena. According to GNU units, the day is 24 hr = 86400 s (which is a historical basis for defining the second, though not the method we officially use now because we have clocks that are more consistent than the Earth's rotation), while the lunar month is 29 days + 12 hours + 44 minutes + 2.8 seconds = 2551442.8 s and the tropical year is 365.242198781 day = 31556926 s If we think of a month as a fixed whole number of days, and/or think of a year as a fixed whole number of months, and/or think of a year as fixed whole number of days, it's been known for thousands of years that we're eventually going to get in trouble astronomically and require some adjustments.

LastTrain 4y ago

Nothing demystifies a subject like putting it into quasi-biblical verse.

zokier 4y ago

Its curious that with the all day additions and removals it still doesn't correct more accurately to the drift. 1 day for 217 years might not be huge, but still feels significant, especially when considering that the julian calendars 1 day per 128 years was deemed unacceptable already back in 16th century. Although I suppose correcting might be tricky without compromising on the lunar cycle accuracy?

wbl 4y ago
There is no Sanhedrin, the only body that could correct this without a schism. As for making the correction a slight mucking about with the molead rules could do it.
- tkk23 4y ago
  There is also the internet. Maybe everybody agrees and there is no objection to a correction? It could be as easy as creating a Mastodon instance to find out.
- jaza 4y ago
  Pan-Jewish changes to Halakha (orthodox law) are still theoretically possible. The last significant such occurrence was the ban on polygamy in Judaism about a millennium ago. It's just a question of how many rabbis, across how many streams of Judaism, would need to reach a consensus, in order for it to be reasonable to consider an amendment as "widely accepted". In terms of changing the calendar rules, I doubt that there would be any chance of pan-Jewish consensus for quite a few more millennia, that is, not until the dates of major festivals get significantly more out of whack than they are now.
  - compsciphd 4y ago
    hey, some (major) rabbis believe that sabbath in japan should be on sunday. (and others believe that in western alaskan islands, it be friday, i.e. if there's a concept of a "date line" in halacha, than the area between the international date line and the halacha date line would be offset by a day depending on which side it is).

connorgutman 4y ago

This Rosh Hashanah I switched to the Jewish calendar full-time. I know this may sound impractical (it is) but it has always felt like an important issue to me as a mostly secular Jewish American. In my opinion the Gregorian calendar offers very little advantage (perhaps even disadvantage) over lunar-solar alternatives. Its popularity has been deeply tied to Christian imperialism and its adoption has often been forced. The Gregorian calendar is technically more accurate as it is off by 27 sec/year (1 day in 3236 years) compared to the Jewish calendar which is off by 7 min/year (1 day in 216 years). This, however, has always felt to me like comparing apples to oranges. The accuracy of the Gregorian calendar comes at the expense of functionality (lunar calculations) which I find to be incredibly useful. With the Jewish calendar you always know what phase the moon is in as the start of each month is a new moon and the middle is a full moon. Not only does this have real-world application in terms of tides, agricultural conditions, night light, animal behaviors, and etc but I have found myself feeling more mindful of nature as a result. It still trips me out that I can go outside and know exactly what the moon is going to look like without googling it! Furthermore, days ending at sundown makes so much more sense to me! There is a certain satisfaction that comes with watching the sunset and it marking the end of your day compared to the day ending in the middle of the night while you are asleep. Lastly, I have felt myself feeling far more connected to my culture as I am more aware of holidays and other traditions that were lost when the Gregorian calendar took over. Some resources for those who are interested: libhdate (Jewish date + cal alternative for Linux) https://sourceforge.net/p/libhdate/wiki/Home/ https://sourceforge.net/p/libhdate/wiki/Home/ hebcal (RSS, CSV, Google/Apple/etc calendar integration) https://www.hebcal.com/ https://www.hebcal.com/ On my android phone I used KLCK and KWGT with the hebcal RSS feed above to create a lockscreen and homescreen Jewish calendar widget. On my laptop I run Sway+Waybar and created a custom waybar module with libhdate. It's not perfect but it's working for now!

willhinsa 4y ago
I’m not Jewish, but that sounds really appealing to me!
js2 4y ago
You might find this book a hoot. I did: https://ajjacobs.com/books/the-year-of-living-biblically/ https://ajjacobs.com/books/the-year-of-living-biblically/

nimbius 4y ago

I had a Jewish friend who once remarked that he knew when rosh hashana and yom Kippur were upon him because it added another forty minutes to his commute in Los angeles. he affectionately called it "the ten days of 'awe come on merge already'"

js2 4y ago
I'm Jewish but I don't get it... am I to take it that Jews going to temple added enough traffic to L.A. to slow down his commute by forty minutes?
- wbl 4y ago
  Probably being extra polite at the expense of using the road effectively
- arrosenberg 4y ago
  Yes, adding several hundred drivers all entering/exiting at the same spot in rush hour at specific spots the 405 can do that. Thinking the one on Mulholland Drive right near the 101/405 interchange.
  - thakoppno 4y ago
    Isn’t that where the skirball center is?
- svat 4y ago
  Tom Lehrer wrote a song called "I'm Spending Hanukkah in Santa Monica" (https://www.youtube.com/watch?v=LslsgH3-UFU https://www.youtube.com/watch?v=LslsgH3-UFU) — I had assumed it was just a joke for the rhyme, but looking at this conversation I'm wondering if there's anything more to it :)
  - antognini 4y ago
    There's something to it, historically LA's Jewish population has been clustered in the West Side.

xwowsersx 4y ago

I highly recommend reading Calendrical Calculations, a book by Edward Reingold and Nachum Dershowitz. It is a beautiful combination of computer science and calendar systems. Also, the Hebrew calendar truly is a marvel, as the book goes through.

dhosek 4y ago

One of the things I love ab out the Hebrew calendar is that the leap month, Veadar is literally “and Adar,” Adar being the month that precedes Veadar.

xwowsersx 4y ago
I've never heard that. As far as I know, it's known as Adar aleph (A) and Adar bet (B)
- schoen 4y ago
  I heard "Adar Rishon" and "Adar Sheni" (written "Adar I" and "Adar II"). I've enjoyed thinking of the latter as like a movie sequel. "Adar II: The Revenge of Adar". Apparently all of these forms are common. https://en.wikipedia.org/wiki/Adar#Names_and_Leap_Years https://en.wikipedia.org/wiki/Adar#Names_and_Leap_Years
  - xwowsersx 4y ago
    Right, that's essentially the same thing, with aleph being a shortened way of saying rishon and bet being a shortened way of saying sheni. My original point was that I'd never heard of "ve'adar". Apparently as the Wikipedia entry says, that's less common. Curious if the Mishna or Talmud ever uses "ve'adar" (I've never seen it, but doesn't mean it doesn't exist)
    - deleted 4y ago
      [deleted]
    - dhosek 4y ago
      I learned it from my Hebrew textbook. The article also uses it, alongside Adar 1 & 2

joelberman 4y ago

It is much easier to calculate eclipses using a lunar calendar. All lunar eclipses happen during a full moon and all solar eclipses during a new moon.

riffic 4y ago

site's author Stephen P. Morse is the architect of the 8086 processor: https://en.wikipedia.org/wiki/Stephen_P._Morse https://en.wikipedia.org/wiki/Stephen_P._Morse

uptownfunk 4y ago

The Jewish are not the only one. In fact the Indian calendars also called panchanga, have a very elaborate system tied to the luni-solar movement and get very detailed into calculation. My guru once jokingly said when he was nominated to lead his specific religious institution, I’ll only agree to head the mission if I Don’t have to deal with the calendar calculation. As there are many parameters which tend to invite debate. Here is one I use almost daily for the Vaishnavite sect I follow. (1) you’ll notice you have to select your time zone and city as some of the holy fast days (also tied to luni-solar movement called ekAdaShi) depend on the sunrise time. Actually this month that we are entering, also known as Kartik, named after the constellation Krttika, where the moon is full, is a very holy month in the Indian calendar and contains the special Diwali festival on the amavasya or new moon night. (1) https://www.purebhakti.com/resources/vaisnava-calendar https://www.purebhakti.com/resources/vaisnava-calendar

dotancohen 4y ago
The full moon falls into a different constellation roughly every month, no?

uptownfunk 4y ago

Would be an interesting paper to compare calendars worldwide. I am seeing many parallels between the Jewish and Hindu calendars. Ours also has an extra month thrown in every few years which is called Adhik Maas, mal maas, or purushottam. This article is quite well written and also entertaining at the same time. I enjoyed it

zx10rse 4y ago

For anyone interested in calendars, check the proto-Bulgarian calendar. It is considered to be one of the oldest if not the oldest, and most accurate in the world by UNESCO. There is a website that rebuild it from the ancient documents describing it, and it is compared head to head with the Gregorian calendar, you can also find the code on github, it is cool. According to it we live in year 7527-th :) Link to the calendar - https://bgkalendar.com/index.php?lang=en https://bgkalendar.com/index.php?lang=en

ossusermivami 4y ago

I remember a long time reading a text file from a package while browsing my /usr/share/docs about the history of Gregorian calendar date in the history, i think it was pretty interesting but I can't find the name of that package of where this was located, (can't seem to be in coreutils/utils-linux except if that has been removed). if anyone would know what i am talking about, i'll be grateful to know the name of the package.

nanna 4y ago

Emacs supports the Hebrew calendar out of the box (alongside Julian, Islamic, Chinese, Mayan, Coptic, French Revolutionary etc etc) but I've never worked out how make much use of it. Anyone have suggestions to get the festivals into Org Agenda, for example?

jaza 4y ago

While in synagogue on Yom Kippur a few days ago, I noticed (for the first time) that the "song of the day" in the Machzor (prayer book just for Yom Kippur) only has options for Monday, Wednesday, Thursday, and Saturday. And it made me think, how can they be so sure that Yom Kippur will never fall on a Sunday, Tuesday, or Friday? Thanks to this wonderful write-up, now I know: the Jewish calendar has a "business rule" that guarantees it!