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    Re: Astronomy: Calculating Positions
    From: Paul Hirose
    Date: 2008 Apr 07, 13:47 -0700

    I wrote:
    > I have a free Windows positional astronomy DLL online which does these
    > things. There's also a C++ example which uses the DLL to compute
    > geocentric and topocentric positions of a star and the Moon.
    > http://home.earthlink.net/~s543t-24dst/sofajpl/lunardist.html
    There's a difference of several arc seconds between the sample run and
    the JPL HORIZONS online calculator. It's a time scale discrepancy. The
    sample run assumes values for (TT-UT1) and (UT1-UTC) which are
    significantly different from the actual values of date used by HORIZONS.
    The USNO MICA program will duplicate the sample run if you use the
    values of TT and the ephemeris longitude of the observer shown in the
    sample run output.
    I should change the parameters so the results match HORIZONS.
    I block messages that contain attachments or HTML.
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