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    Re: Almanac data
    From: Frank Reed
    Date: 2009 Jun 4, 23:40 -0700

    Last week, I wrote regarding Peter Hakel's Moon spreadsheet:
    "I tried out some dates and noticed that the Moon's position is right on the 
    money for 2009, but it's a few tenths of a minute of arc off c.1950 and a 
    couple of minutes of arc out if I go back two centuries. Those are fairly big 
    error for lunars. It appears that you're using a simple expression for 
    delta-T that's quadratic in time."
    Peter sent me a revised version to preview with expanded delta-T calculations, 
    and his numbers now agree with with the almanac data from my software to 
    within two or three seconds of arc of difference at most, usually less. We've 
    used entirely different approaches to generate the ephemerides, so the 
    agreement is not due to identical implementation of the algorithms or any 
    other "lucky accident".
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