# How does the Jewish year work? **URL:** \ **Category:** Factual Questions\ **Created:** [October 10, 2000, 4:12am UTC](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366 "2000-10-10T04:12:06Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Moe](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/moe/32/2972_2.png) [@Moe](https://boards.straightdope.com/u/Moe)\ **Post date:** [October 10, 2000, 4:12am UTC](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366/1 "2000-10-10T04:12:06Z")
OK I’ve grown up in a Jewish household, even attended Hebrew school for 5 years, but I don’t get the Jewish year. Why do the jewish holidays fall on different dates every year? It must be a 365 day year because the holidays don’t seem to be occuring perpetually earlier or later in the year, just different. Am I missing something really obvious here? ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [October 10, 2000, 4:38am UTC](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366/2 "2000-10-10T04:38:07Z")
I believe it’s a lunar calendar, but don’t quote me on that. ---
**Author:** ![Junior\_Spaceman](https://avatars.discourse-cdn.com/v4/letter/j/eb8c5e/32.png) [@Junior\_Spaceman](https://boards.straightdope.com/u/Junior_Spaceman)\ **Post date:** [October 10, 2000, 4:45am UTC](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366/3 "2000-10-10T04:45:26Z")
OTOH, It’s a lunar year, with twelve months in most years. A lunar month corresponds to a lunar cycle, and so is more consistent in length than the months we use. Every four years, there is a leap year, where there is an extra month added, so that the year does not go out of alignment (which it would very rapidly at a week per year). Every four years, the secular date that corresponds with a date in the Hebrew calendar, eg Yom Kippur, should be very close (if not exactly the same). I’m not sure how the smaller discrepencies are accounted for, similar to how we do not have a leap year on a century that does not divide by 400. HenrySpencer ---
**Author:** ![Kyla](https://avatars.discourse-cdn.com/v4/letter/k/eada6e/32.png) [@Kyla](https://boards.straightdope.com/u/Kyla)\ **Post date:** [October 10, 2000, 5:20am UTC](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366/4 "2000-10-10T05:20:01Z")
To clarify HenrySpencer’s point: From [jewfaq.org](http://jewfaq.org): > [@](#): > > In the fourth century, Hillel II established a fixed calendar based on mathematical and astronomical calculations. This calendar, still in use, standardized the length of months and the addition of months over the course > of a 19 year cycle, so that the lunar calendar realigns with the solar years. Adar II is added in the 3rd, 6th, 8th, 11th, 14th, 17th and 19th years of the cycle. The current cycle began in Jewish year 5758 (the year that began October 2, 1997). Adar is a regular month. Adar II (or Adar Bet) is the occasional additional month. A Hebrew day will line up with a Gregorian day every nineteen years. My Hebrew birthday is the 25th of Tammuz. This generally drifts around the end of July and beginning of August, but on my ninteenth birthday, 25 Tammuz and 19 July were once again matched up. Interestingly, the Islamic calendar is also a lunar calendar, but doesn’t compensate with the thirteenth month (as per Muhammed’s instuction). As a result, the month drift slowly through the seasons. The word Ramadan means “scorcher”, because the month used to fall in the summer months, but currently, Ramadan is a winter month. BTW, Moe, thanks for giving me a good topic to talk about in my Hebrew school class! ---
**Author:** ![Kyla](https://avatars.discourse-cdn.com/v4/letter/k/eada6e/32.png) [@Kyla](https://boards.straightdope.com/u/Kyla)\ **Post date:** [October 10, 2000, 5:21am UTC](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366/5 "2000-10-10T05:21:51Z")
…I made a typo. My Gregorian birthday is 29 July, not 19. ---
**Author:** ![C\_K\_Dexter\_Haven](https://avatars.discourse-cdn.com/v4/letter/c/b2d939/32.png) [@C\_K\_Dexter\_Haven](https://boards.straightdope.com/u/C_K_Dexter_Haven)\ **Post date:** [October 10, 2000, 12:52pm UTC](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366/6 "2000-10-10T12:52:59Z")
Please note, Henry has got the broad concepts sort of right, but the details WRONG. It is not the case that a leap year occurs every four years in the Jewish calendar. It is also not the case that after every leap year, the two calendars (Jewish and common) coincide. The Jewish calendar is based on a lunar cycle (that is, each month is based on the interval, about 29 or 30 days, from new moon to new moon). The month begins at the new moon. However, the lunar cycle of twelve months is therefore short by about 11 days per solar year. Since the Jewish holidays are supposed to be season-related (they were originally harvest festivals), the calendar adjusts by adding a whole month approximately every three years–actually, 7 times every 19 years, as Kyla quoted. The calculations are precise but VERY complicated. A further complication is that the number of days in a month can change slightly (29 or 30)depending on exactly when the new moon occurs (like, if the new moon occurs shortly after sunset…) There are other complications, so that (for example) Rosh Hashonah cannot fall on certain days of the week (like, Friday or Sunday) because that would impose severe difficulty on account of the interaction with Saturday (Sabbath). In contrast, as Kyla notes, the Moslem calendar is also lunar, but does not adjust for the difference. The holidays are therefore not seasonal; while Ramadan is now in the winter (in the U.S.), it will shift slowly (by about 11 days each year) so that in thirty years or so, it will be in the summer (in the U.S.). Since Ramandan is a month of fasting during daylight hours, it is much easier now when the daylight hours are shorter than it will be in thirty years when daylight hours are longer. I also should respond to Moe’s OP comment: \<\< Why do the jewish holidays fall on different dates every year? \>\> …Well, that’s not so. The Jewish holidays always fall on the same day each year. Yom Kippur, for example, always falls on the 10th day of Tishri, and Passover always falls on the 14th day of Nissan. BTW, in Israel, they tend to use both dates, Hebrew calendar and solar calendar (Gregorian). Hope that helps. ---
**Author:** ![cmkeller](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cmkeller/32/118_2.png) [@cmkeller](https://boards.straightdope.com/u/cmkeller)\ **Post date:** [October 10, 2000, 3:01pm UTC](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366/7 "2000-10-10T15:01:05Z")
Just a minor correction: CKDextHavn said: > [@](#): > > A further complication is that the number of days in a month can change slightly (29 or 30)depending on exactly when the new moon occurs (like, if the new moon occurs shortly after sunset…) Actually, only two months of the year, Heshvan and Kislev, are variant in that regard. Each of the other months is always 29 days or always 30 days, pretty much on an alternating schedule. ---
**Author:** ![TheThill](https://avatars.discourse-cdn.com/v4/letter/t/35a633/32.png) [@TheThill](https://boards.straightdope.com/u/TheThill)\ **Post date:** [October 10, 2000, 3:05pm UTC](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366/8 "2000-10-10T15:05:46Z")
Just to clarify: In Israel, both calendars are in use, but with a definite preference for the secular, Gregorian calendar. If you ask someone on the street what date it is, you’ll only get one answer. If you ask what the Jewish date is, you’re more likely to get a very strange look. ---
**Author:** ![Moe](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/moe/32/2972_2.png) [@Moe](https://boards.straightdope.com/u/Moe)\ **Post date:** [October 10, 2000, 3:12pm UTC](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366/9 "2000-10-10T15:12:44Z")
> [@](#): > > \*Originally posted by Kyla \* > BTW, Moe, thanks for giving me a good topic to talk about in my Hebrew school class! My pleasure Kyle. Thanks for answering my question. And thanks CK, as always for your awesome insight. ---
**Author:** ![JoltSucker](https://avatars.discourse-cdn.com/v4/letter/j/d2c977/32.png) [@JoltSucker](https://boards.straightdope.com/u/JoltSucker)\ **Post date:** [October 10, 2000, 4:28pm UTC](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366/10 "2000-10-10T16:28:49Z")
**CKDextHavn** , > [@](#): > > There are other complications, so that (for example) Rosh Hashonah cannot fall on certain days of the week (like, Friday or Sunday) because that would impose severe difficulty on account of the interaction with Saturday (Sabbath). I’m a little confused here. We Reform Jews just celebrated Rosh Hashannah last Friday night/Saturday morning, complete with additional Shabbat-related verbage in the liturgy. Is that a Reform-specific differences in the calendar. BTW, Shannah Tovah! ---
**Author:** ![cmkeller](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cmkeller/32/118_2.png) [@cmkeller](https://boards.straightdope.com/u/cmkeller)\ **Post date:** [October 10, 2000, 4:40pm UTC](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366/11 "2000-10-10T16:40:16Z")
JoltSucker: > [@](#): > > I’m a little confused here. We Reform Jews just celebrated Rosh Hashannah last Friday night/Saturday morning, complete with additional Shabbat-related verbage in the liturgy. Is that a Reform-specific differences in the calendar. What CK meant was that the first **day** of Rosh Hashanna will never come out on Friday or Sunday, i.e., the first night won’t be Thursday night or Saturday night. The “difficulty on account of the interaction with Saturday (Sabbath)” CK refers to is in relation to Yom Kippur: if Yom Kippur would fall on Friday or Sunday (a consequence of the first day of Rosh Hashannah being Wednesday, another day of the week Rosh Hashannah can’t come out on, or Friday…if I recall correctly, Sunday was a different reason), you’d have two consecutive days on which a dead body can’t (according to Jewish law) be moved, which would be a pretty bad thing, if someone were to die immediately prior to, or immediately at the start of, the Sabbath/Yom Kippur combination. Chaim Mattis Keller ---
**Author:** ![Johanna](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/johanna/32/8318_2.png) [@Johanna](https://boards.straightdope.com/u/Johanna)\ **Post date:** [October 10, 2000, 4:53pm UTC](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366/12 "2000-10-10T16:53:49Z")
The Islamic lunar calendar cycles through the seasons every thirty-two solar years. Making an extra year. Therefore the ratio is thirty-three lunar years to every thirty-two solar years. (Muslims get older more quickly. E.g. instead of singing “When I’m Sixty-Four” they sing “When I’m Sixty-Six”.) An Islamic date that falls at the winter solstice this year will fall around the summer solstice about sixteen years from now, about half the cycle. Thus Muslims living in the Southern Hemisphere (there are lots of them in South Africa) get their turn at shorter fasting days in winter Ramadans, as much as do people in the Northern Hemisphere. It’s fair all around. ---
**Author:** ![C\_K\_Dexter\_Haven](https://avatars.discourse-cdn.com/v4/letter/c/b2d939/32.png) [@C\_K\_Dexter\_Haven](https://boards.straightdope.com/u/C_K_Dexter_Haven)\ **Post date:** [October 10, 2000, 4:59pm UTC](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366/13 "2000-10-10T16:59:51Z")
I was trying desparately NOT to get into that level of details, and to just wave my hands and say “It’s complicated but predictable once you know all the rules.” And my apologies for the night/day issue; the “day” in Jewish law runs from sunset to sunset (rather than midnight to midnight); partly because it was easier to determine in pre-clock days, and partly because the Bible verses read, “There was evening, there was morning, the Xth Day.” CM, while I greatly respect your learning, I wonder if you’ve got this one right. There are plenty of two day periods when a body can’t be buried, like any Rosh Hashonah or Pesakh. The restriction may involve no three-day non-working days, though. I was taught that the reason for not allowing Yom Kippur on Thursday night/Friday is that you couldn’t prepare the Sabbath meal for Friday night (since you can’t cook on Yom Kippur.) And the reason for not allowing Yom Kippur on a Saturday night/Sunday is the same in reverse, you wouldn’t be able to cook the pre-Yom Kippur dinner on Shabbat. I think for the same reason, the first seder can’t fall on a Thursday or Saturday night, although I’d need to check that… I suffer CRS syndrome (Can’t Remember Sh\*t). Oh, and CM – l’shana tova! ---
**Author:** ![barbitu8](https://avatars.discourse-cdn.com/v4/letter/b/839c29/32.png) [@barbitu8](https://boards.straightdope.com/u/barbitu8)\ **Post date:** [October 10, 2000, 5:17pm UTC](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366/14 "2000-10-10T17:17:27Z")
> [@](#): > > \*Originally posted by CKDextHavn \* > \*\* > A further complication is that the number of days in a month can change slightly (29 or 30)depending on exactly when the new moon occurs (like, if the new moon occurs shortly after sunset…) > > Hope that helps. \*\* This hasn’t helped me in the least, but has totally confused me, inasmuch as a new moon only occurs during the daytime. As I understand it, the moon is new when no part of it facing us reflects any sunlight. If the moon is still visible after sunset, it would be reflecting some sunlight and cannot be new. Perhaps you can enlighten me how this is possible (pun intended). ---
**Author:** ![sdimbert](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sdimbert/32/20204_2.png) [@sdimbert](https://boards.straightdope.com/u/sdimbert)\ **Post date:** [October 10, 2000, 5:34pm UTC](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366/15 "2000-10-10T17:34:19Z")
From [http://www.jewfaq.org/calendar.htm:](http://www.jewfaq.org/calendar.htm:) > [@](#): > > The Jewish calendar is primarily lunar, with each month beginning on the new moon, when the first sliver of moon becomes visible after the dark of the moon. In ancient times, the new months used to be determined by observation. When people observed the new moon, they would notify the Sanhedrin. When the Sanhedrin heard testimony from two independent, reliable eyewitnesses that the new moon occurred on a certain date, they would declare the rosh chodesh (first of the month) and send out messengers to tell people when the month began. > > The problem with strictly lunar calendars is that there are approximately 12.4 lunar months in every solar year, so a 12-month lunar calendar loses about 11 days every year and a 13-month lunar gains about 19 days every year. The months on such a calendar “drift” relative to the solar year. On a 12 month calendar, the month of Nissan, which is supposed to occur in the Spring, occurs 11 days earlier each year, eventually occurring in the Winter, the Fall, the Summer, and then the Spring again. To compensate for this drift, an extra month was occasionally added: a second month of Adar. The month of Nissan would occur 11 days earlier for two or three years, and then would jump forward 29 or 30 days, balancing out the drift. > > In the fourth century, Hillel II established a fixed calendar based on mathematical and astronomical calculations. This calendar, still in use, standardized the length of months and the addition of months over the course of a 19 year cycle, so that the lunar calendar realigns with the solar years. Adar II is added in the 3rd, 6th, 8th, 11th, 14th, 17th and 19th years of the cycle. The current cycle began in Jewish year 5758 (the year that began October 2, 1997). > > In addition, Yom Kippur should not fall adjacent to Shabbat, because this would cause difficulties in coordinating the fast with Shabbat, and Hoshanah Rabba should not fall on Saturday because it would interfere with the holiday’s observances. A day is added to the month of Cheshvan or subtracted from the month of Kislev of the previous year to prevent these things from happening. Hope this helps. ---
**Author:** ![C\_K\_Dexter\_Haven](https://avatars.discourse-cdn.com/v4/letter/c/b2d939/32.png) [@C\_K\_Dexter\_Haven](https://boards.straightdope.com/u/C_K_Dexter_Haven)\ **Post date:** [October 10, 2000, 5:51pm UTC](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366/16 "2000-10-10T17:51:33Z")
\<\< If the moon is still visible after sunset, it would be reflecting some sunlight and cannot be new. Perhaps you can enlighten me how this is possible (pun intended). \>\> ??? I don’t follow your question. You’re saying that there can never be a new moon because the “new” moon is not visible on earth? The moon is visible when it’s new, just the way that the darkened part is visible when the moon is crescent. ---
**Author:** ![cmkeller](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cmkeller/32/118_2.png) [@cmkeller](https://boards.straightdope.com/u/cmkeller)\ **Post date:** [October 10, 2000, 6:06pm UTC](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366/17 "2000-10-10T18:06:48Z")
CKDextHavn: > [@](#): > > CM, while I greatly respect your learning, I wonder if you’ve got this one right. There are plenty of two day periods when a body can’t be buried, like any Rosh Hashonah or Pesakh. The restriction may involve no three-day non-working days, though. Re-read my original post; you’ll notice that I said the dead body can’t be **moved** , not that it can’t be **buried**. All holidays that fall on weekdays allow people to carry things in the public domain…except Yom Kippur. And the first Seder definitely _can_ fall on Saturday night. For Passover, it’s Sunday, Tuesday and Thursday nights that the first Seder can’t come out, though I don’t recall a reason for it. And l’Shana Tova to you as well – and to everybody here on the boards! Chaim Mattis Keller ---
**Author:** ![mellonhead](https://avatars.discourse-cdn.com/v4/letter/m/e19adc/32.png) [@mellonhead](https://boards.straightdope.com/u/mellonhead)\ **Post date:** [October 10, 2000, 7:05pm UTC](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366/18 "2000-10-10T19:05:03Z")
> [@](#): > > \*Originally posted by HenrySpencer \* > \*\* > I’m not sure how the smaller discrepencies are accounted for, similar to how we do not have a leap year on a century that does not divide by 400. > > HenrySpencer \*\* I got this from the “[learningkingdom.com](http://learningkingdom.com)” website… "In 1582 Pope Gregory decreed that October’s dates would skip from the fourth to the fifteenth, dropping ten days. The reason for this seemingly strange act had to do with the calendar system that was in use at the time. In 1582 Pope Gregory decreed that October’s dates would skip from the fourth to the fifteenth, dropping ten days. The reason for this seemingly strange act had to do with the calendar system that was in use at the time. Unlike our current system, the old Julian calendar had a leap year every four years without exception. Because a year is really a fraction shorter than 365.25 days, tiny errors began to accumulate. By the time of Pope Gregory’s decree, the calendar was adjusted by ten days compared to Earth’s solar year. When he issued his decree, Gregory also fixed the leap year rule, so that leap years do not occur on century years (divisible by 100), unless the year is also divisible by 400. There is one other exception: years divisible by 4000 are not leap years. For example, 1900 was not a leap year, but 2000 is one." ---
**Author:** ![C\_K\_Dexter\_Haven](https://avatars.discourse-cdn.com/v4/letter/c/b2d939/32.png) [@C\_K\_Dexter\_Haven](https://boards.straightdope.com/u/C_K_Dexter_Haven)\ **Post date:** [October 10, 2000, 9:10pm UTC](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366/19 "2000-10-10T21:10:54Z")
Aha, thanks for the clarification, CM. What I get for doing this at work, from memory, and trying to type quickly… As I say, I’d always heard the explanation had to do with cooking rather than moving bodies, but I dunno. It may just have been one of R. Hillel’s little quirks. And Mellonhead, if you go searching the Mailbag, you’ll find an extravagant discussion by Straight Dope Staff Dex (c’est moi!) on the leap year subject in the Gregorian calendars, with reference to the Julian, Jewish, and Islamic calendars: [Why do we have leap years?](http://www.straightdope.com/mailbag/mleapyr.html) [Edited by CKDextHavn on 10-10-2000 at 04:13 PM] ---
**Author:** ![zev\_steinhardt](https://avatars.discourse-cdn.com/v4/letter/z/97f17d/32.png) [@zev\_steinhardt](https://boards.straightdope.com/u/zev_steinhardt)\ **Post date:** [October 10, 2000, 9:22pm UTC](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366/20 "2000-10-10T21:22:42Z")
> [@](#): > > \*Originally posted by cmkeller \* > \*\*And the first Seder definitely _can_ fall on Saturday night. > Chaim Mattis Keller \*\* As it does this year. 🙂 Zev Steinhardt [Next page](https://boards.straightdope.com/t/how-does-the-jewish-year-work/36366.md?page=2)