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    Re: Old style lunar
    From: Frank Reed CT
    Date: 2004 Dec 10, 15:50 EST
    I wrote earlier:
    >It's no longer necessary to do this algorithmically. Just open a virtual
    >almanac page.
    George H asked:
    "What about if you need those predictions when you're at sea? I ask."
     
    Since we're comparing Meeus algorithms with a straight database based on JPL integrations, I assume that a computing device is permitted. The software and data to do this by database for a year is approximately the same size as the software to do it algorithmically, and it is many times more accurate for the Moon's position. For longer stretches of time, the database grows in size linearly. Many people approaching this problem look at the original JPL database which is hundreds of megabytes for a century of data and assume that that's too big to be practical. But there are a variety of straight-forward techniques that can reduce the size to ten megabytes for 300 years. That's the whole size (ten megs) of the database behind my online 300-year almanac and lunar distance predictor. The code to access it is just a couple of hundred kilobytes.
     
    Believe me, I used to be quite fanatic about algorithmic approaches a la Meeus, Chapront-Touze etc. Then I realized that the whole approach was absurd for the vast majority of "practical" applications. The positions of the planets have *already* been calculated using numerical integrations that include such tiny factors as the gravitational perturbations induced by the largest asteroids. The almanac exists. We don't need to re-calculate it every time we want the position of the Moon.
     
    Frank R
    [ ] Mystic, Connecticut
    [X] Chicago, Illinois
       
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