(c) 2000 Dr Hendel; 1st appeared in Torah Forum (c) Project Genesis

Date: Sun, 19 Mar 2000 20:09:22 -0500 (EST)
From: Russell Hendel <  rhendel@mcs.drexel.edu>
Subject: Re: Day 8

<  <  ...When did the Rabbi's sit down and agree... Today is Tuesday, Year
2346. Is there a date in history that our ancestors decided was a start
date of the calender...>  >

There are only 2-3 basic rules governing the answer to this question

During the time of the temples the Sanhedrin (the equivalant of our
congress sat and reviewed WHEN the month and/or YEAR should begin each
month. Some months were 29 days and some were 30; some years had 12 months
and some had 13. While witnesses had to come and say they saw the moon, the
final determination was made by the court.

After the destruction of the temple our current calendar was 'fixed'--
based on a few simple rules given below. The purpose of these rules was to
make calculations easy (See Rambam, Laws of Months Chap 6-10 for a more
detailed computation). This is the same calendar that we use today.
Although many programs exist for calendar making, these rules could easily
be codified into an excel spreadsheet.

The rules governing the calendar are the following: (a) months are 29 or 30
days; (b) years are 12 or 13 months; (c) The calendar works in cycles of 19
years with years 3,6,9,11,14,17 leap years; (d) the lunar month is 29 days,
12 hours and 793/1080ths of an hour (e) The first lunar month started on
Monday 11 at night at 204/1080ths after the hour (f) The first month of the
year is always 30 days, the next two months may be either both 29, both 30
or 29, for month 2 and 30 for month 3, and the remaining months alternate
(29,30,...). (g) The laws governing the 2nd and 3rd month depend on the
relative distance of the new year days in the 2 consecutive years (h) The
declaration of WHEN the month begins is the same day as when the lunar
conjunction occurs except in 4 cases.

I note in passing that the "Monday 11PM 204/1080ths" time for the first
month is 'fictitious'---it is a number that exists only for calculational
purposes since all calculations are 'approximate'. The talmud refers to the
first month in year 0 as the 'conjunction during nullility'. The time used
(Monday 11 PM..) is based on the assumption that Adam was created on Friday
(New Year 1) and the sun was created on Wednesday (6:00 PM). The
calculations honor the two traditions that the world was created either in
April or September.

I hope this brief summary helps. If you need help in constructing a
spreadsheet let me know offline

Russell Jay Hendel; Phd ASA;
Moderator Rashi is Simple, http://www.shamash.org/rashi/