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From: rhendel@mcs.drexel.edu (Russell Hendel)
Date: Thu, 3 Oct 1996 19:57:41 -0400
Subject: Birchat Chama vs Harath Olam; 2 sources for Jewish Calendar

Rick Turkel [V25n6] inquires why HARATH OLAM refers to Tishray as the
creation of the world but nevertheless Bircath Chama revolves around the
sun returning to its original position in Nissan.

The simple answer is that the Jewish calendar has two conflicting
sources.  Very roughly, the lunar months and years start in Tishray when
the world was created while leap years are depedent on when Spring and
Pessach fall out which according to Ex 12,1 is connected with Nissan.  A
complete account may be found in Rambam, Calendar laws, 6-10. Some
details are as follows

THE LUNAR PROBLEM: The lunar month is about 29.5 days; but we cant start
a month in the middle of the day (6:5, and 8:1). The SOLUTION is to make
full and empty months (e.g. 8:6)--some being 29 and some 30.  This
requires calculating when the lunar conjunction occurs and these
CALCULATIONS start from the first lunar month in the first
Tishray(6:15,10:3).

THE SOLAR PROBLEM: Just as a month cannot start in the middle of a day
so too the solar year---when the earth returns to its original
position--cannot take place in the middle of a month(9:1). The SOLUTION
to this problem is to make leap and non leap years(6:10).  This requires
calculating the position of the sun against the background of stars and
this calculation always starts from its position in Nisan(10:3).  The
reason for this is because the court had to decide when to make a year a
leap year to e.g. let Pesach coincide with the spring (10:6).

The SOLAR CYCLE--the time required for the sun to return to its original
position is 28 years.  The LUNAR_SOLAR cycle--the time required for a
pattern of leap and non leap years with full and deficient months to
return to its starting point (with a 1-2 hour error) is 19 years.

I hope this clarifies the matter.  Incidentally, similar problems and
resolutions exist in most other cultures.

Russell Hendel, Ph.d., ASA, rhendel @ mcs drexel edu