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 --- 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.