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From: raphael@crystal.UUCP
Newsgroups: net.religion.jewish
Subject: Re: Moled -- Why is it always not on the same day as Rosh Chodesh
Message-ID: <421@crystal.UUCP>
Date: Thu, 14-Mar-85 18:27:00 EST
Article-I.D.: crystal.421
Posted: Thu Mar 14 18:27:00 1985
Date-Received: Sun, 17-Mar-85 00:24:45 EST
References: <146@pyuxww.UUCP> <9039@brl-tgr.ARPA> <520@sfmag.UUCP> <5458@ucbvax.ARPA>
Organization: U of Wisconsin CS Dept
Lines: 29

Why is the Molad not always the same day as Rosh Khodesh?
Because of several sources of discrepancy:

1.  The molad is calculated by a fixed formula, which is erroneous by about
one second every month.  It is currently about 4 hours off from the true
instant of new moon.  This accuracy is perfect within the grain of the
calculation, which has 3-1/3 seconds as the smallest unit.

2.  The time of the molad is given in Jerusalem Standard (not mean) time.  

3.  The day of Rosh Khodesh is calculated by a fixed formula that gives each
month a set number of days.  (The second and third months have either 29 or 30
days depending on the total number of days in the year, but the formula is
fixed.)  Rosh HaShono is usually pretty close to the first Molad (although it
can be delayed by 2 days for various reasons, such as to prevent Yom Kippur
from falling on Friday).  Near the middle of the year, the discrepancy between
Molad and Rosh Khodesh can be fairly large (a day or so).

4.  Months that have 30 days cause the Rosh Khodesh of the next month to be
celebrated for two days, on the 30th of the previous month and the 1st of the
next one.  So one shouldn't expect the Molad to fall near the first of those
two.

By the way, almost every published calendar I have seen gave the wrong time for
the Molad a few months ago.  I wonder why we so carefully announce the Molad in
shul, since it seems fairly unimportant.

	Raphael Finkel
	raphael@uwvax (arpa or csnet)