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This site explains that there are 4 rules that would cause Rosh Hashannah to be postponed 1 or 2 days after the date of Molad Tishrei. You can view all 4 rules on the web site, but rule 4 states:

4) If molad Tishri following a leap year falls on Monday at 15 hr 589 hq (9:32:43 1/3 AM) or later, Tishri 1 is delayed by one day for the following reason:

Molad Tishri of the leap year occurred on or after Tuesday at 18hr (noon) Therefore Tishri 1 of that leap year was delayed one day by (2 - Molad Zaken rule) and one more day by (1 - Lo Ad"u Rosh rule) This would make that leap year too short (382 days) Note that this delay would now cause Tishri 1 to fall on a Tuesday and that will never cause (1) to trigger a further delay

I have designed an Excel sheet with some Visual Basic programming to list the dates of Rosh Hashannah and tell me the postponement rules (if any) that were applied. I have listed all years from 5775 until 5900. I have not been able to locate any instance where this rule has been applied. Granted, I may have a logic error in my program, so perhaps, it exists after all.

Would anyone know when this rule was last applied and when the next occurrence would occur? Also, if you know of a quick way to determine this programmatically (VNA or psudeu code), I'd really appreciate that.

While I'm at it - Shana Tovah to all.

Double AA
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DanF
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  • Just as a rough estimate, the rule only applies if it falls between 15.589 and 18 hours which is 2651 Chalakim. There are 181440 Chalakim in a week, so the Molad should occur at the right time about 1.5% of the time. But leap years are only 7/19, so the Molad at the right time after a leap year is only 0.5% of the time, or once every 200 years. You only checked 125 years, so you shouldn't have been surprised to have missed it. – Double AA May 16 '16 at 19:45

1 Answers1

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It has been used 11 times so far since the enactment of the fixed calendar in 4119. It was used in 4179, 4257, 4504, 4602, 4849, 5096, 5194, 5441, 5519, 5688, and 5766. The next time it will be used is 6013 if we still have a fixed calendar then. You can read about this exceedingly rare Dechiya and its history here.

msh210
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Double AA
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  • Thanks for the research and the link. I'll have to brush up on my Ivrit a bit :-) Shanah Tovah – DanF Sep 23 '14 at 03:23
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    +1 - the date of the enactment of the calendar is known with such precision? – Y     e     z Sep 23 '14 at 03:25
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    @YEZ Apparently it's based on some Teshuva from the Geonim. I wouldn't take it as an Ikkar Emunah. – Double AA Sep 23 '14 at 05:34
  • @Yez http://www.hakirah.org/Vol20Ajdler.pdf – Double AA Oct 19 '16 at 02:00
  • Years of Betutakpat 75 153 322 400 647 745 992 1239 1584 1662 1831 1909 2078 2156 2501 2748 3093 3340 3587 3685 3932 4010 4179 4257 4504 4602 4849 5096 5194 5441 5519 5688 5766 6013 6111 6358 6605 6950 – Double AA Jun 10 '20 at 19:42
  • Years of Gatrad 7 34 85 105 176 183 203 254 281 301 332 352 379 423 430 450 501 528 548 579 599 626 677 697 704 775 795 826 846 873 924 944 951 1022 1042 1093 1120 1171 1191 1198 1218 1269 1289 1296 1340 1367 1418 1438 1445 1465 1516 1536 1543 1614 1685 1692 1712 1763 1783 1790 1810 1861 1932 1939 1959 2010 2030 2037 2057 2108 2135 2186 2206 2213 2257 2277 2284 2304 2355 2382 2433 2453 2460 2524 2531 2551 2602 2629 2680 2700 2707 2727 2778 2798 2849 2876 2927 2947 2954 2974 3025 3045 3052 3123 3174 3194 3201 3221 3272 3292 3299 3319 3370 3441 3448 3468... – Double AA Jun 10 '20 at 19:46
  • ... 3519 3539 3546 3566 3617 3644 3695 3715 3766 3786 3793 3813 3864 3891 3911 3942 3962 4033 4040 4060 4111 4138 4158 4189 4209 4236 4287 4307 4358 4385 4405 4436 4456 4483 4534 4554 4561 4632 4652 4683 4703 4730 4781 4801 4808 4828 4879 4899 4950 4977 5028 5048 5055 5075 5126 5146 5153 5224 5275 5295 5302 5322 5373 5393 5400 5471 5542 5549 5569 5620 5640 5647 5667 5718 5745 5789 5796 5816 5867 5887 5894 5914 5965 5992 6043 6063 6070 6134 6141 6161 6212 6239 6290 6310 6317 6381 6388 6408 6459 6486 6537 6557 6564 6584 6635 6655 6662 6706 6733 6784 6804 6811 6831 6882 6902 6909 6980 – Double AA Jun 10 '20 at 19:46
  • Link in the answer is broken – Joel K Apr 16 '23 at 08:26