Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.1 6/24/83; site seismo.UUCP
Path: utzoo!watmath!clyde!floyd!harpo!seismo!flinn
From: flinn@seismo.UUCP (E. A. Flinn)
Newsgroups: net.astro
Subject: Re: astronomical references/algorithms wanted
Message-ID: <718@seismo.UUCP>
Date: Mon, 19-Mar-84 11:06:25 EST
Article-I.D.: seismo.718
Posted: Mon Mar 19 11:06:25 1984
Date-Received: Tue, 20-Mar-84 01:32:15 EST
References: <424@sequent.UUCP>, <235@deepthot.UUCP>
Organization: Center for Seismic Studies, Arlington, VA
Lines: 17

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I just posted a note to net.micro, where I saw somebody saying that he
had looked up the length of the lunar synodic month in a handbook, and
then used that number to calculate phase of the moon at any other
time.  The Moon's orbit is seriously perturbed by gravitational
attraction of other bodies in the solar system, and by its own and the
other bodies' deviations from spherical symmetry, so the synodic
period varies a good deal - 1% or so.  You wouldn't have to
extrapolate very many periods before you began to get the phases
wrong.

Serious lunar phase calculators should consider trying to get copies
of the lunar ephemeris tapes from JPL or the University of Texas at
Austin - the latter have been doing lunar laser ranging since 1979,
and can tell you the position of the Moon to within a foot or so.