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Overpost Overview

Overpost Overview

by Remy Landau


The excess of time of the molad over the first day of any month will be referred to as the overpost.

The length of the molad periods for 1, 2 and 4 months are

MOLAD PERIOD LENGTHS
MONTHS LENGTH
129d 12h 793p
259d 1h 506p
4118d 2h 1012p

Shevat's Overpost In A 383-Day Year

383-DAY YEAR MAXIMUM OVERPOSTS
  KISLEVSHEVAT
  DAYTIMEDAYTIME
Maximum Molad of Tishrei Tishrei 12h 490pTishrei 12h 490p
Molad Period From Tishrei59d1h 506p 118d2h 1012p
Maximum Molad Time Tishrei 603h 996pTishrei 1195h 422p
First Day of Month Tishrei 60 Tishrei 118 
Maximum Overpost Possible none 5h 422p

In any 383-day year, the latest possible molad of Tishrei is on Tishrei 1 at 2h 490p
since 2h 491p + 383d 21h 589p = 384d.
Hence, the maximum molad of Shevat is day 1 at 2h 490p + 118d 2h 1012p = day 119 at 5h 422p.
In any 383-day year, the first day of Shevat is day 1 + (30 + 29 + 29 + 29) = day 118 of that year.
Hence, for the 383-day year, the maximum overpost of Shevat = 5h 422p.

Kislev's Overpost In A 384-Day Year

384-DAY YEAR MAXIMUM OVERPOSTS
  KISLEVSHEVAT
  DAYTIMEDAYTIME
Maximum Molad of Tishrei Tishrei 123h 1079pTishrei 123h 1079p
Molad Period From Tishrei59d1h 506p 118d2h 1012p
Maximum Molad Time Tishrei 611h 505pTishrei 1202h 1011p
First Day of Month Tishrei 60 Tishrei 119 
Maximum Overpost Possible 1h 505p 2h 1011p

In any 384-day year, the latest possible molad of Tishrei is on Tishrei 1 at 23h 1079p.
Hence, the maximum molad of Kislev is day 1 at 23h 1079p + 59d 1h 506p = day 61 at 1h 505p.
In any 384-day year, the first day of Kislev is day 1 + (30 + 29) = day 60 of that year.
Hence, for the 384-day year, the maximum overpost of Kislev = 1h 505p.

Shevat's Overpost In A 384-Day Year

In any 384-day year, the latest possible molad of Tishrei is on Tishrei 1 at 23h 1079p.
Hence, the maximum molad of Shevat is day 1 at 23h 1079p + 118d 2h 1012p = day 120 at 2h 1011p.
In any 384-day year, the first day of Shevat is day 1 + (30 + 29 + 30 + 29) = day 119 of that year.
Hence, for the 384-day year, the maximum overpost of Shevat = 2h 1011p.

Dehiyah Molad Zaqen

It is easily shown that no other month of the Hebrew calendar has any overpost.
Therefore, the maximum overpost possible for any month is the maximum overpost of Shevat = 5h 422p.

To avoid the overpost problem for all possibilities, the subsequent year must not be allowed to start with its molad greater than Tishrei 1 at (23h 1079p - (5h 422p)) = 18h 657p.

The Hebrew calendar scholars, possibly between years 4595H (835g) and 4680H (920g), introduced with a limiting time of 18h, the Tishrei 1 postponement rule known as Dehiyah Molad Zaqen.

In 4680H (920g), Reb Aaron ben Meir of Jerusalem wanted this limit upgraded to 18h 642p, even though that value could have been as much as 18h 657p.

Saadia ben Yosef, later to be known as Saadia Gaon, opposed ben Meir's change. Due to the infrequency of this calendar event (about once every 180 years or so) the matter was forgotten sometimes after 4687H (927g) and the 18h limit remained intact, most probably because of its numerical simplicity. (See also The Ben Meir Years).

Please see Understanding Dehiyah Molad Zaqen for a more rigorous analysis of the overpost problem.


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Remy Landau

First  Paged  7 Nov 2006
Next Revised 22 Jan 2007