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    Re: Errors in USNO celestial data
    From: Antoine Couëtte
    Date: 2010 May 3, 01:15 -0700

    Yes, Douglas,

    your Dynamical time will be correct, accordingly, RA and D will be correct, ...

    ... however your UT will not be correct if you use the method you just described.

    If your RA and D are correct, your Greenwhich Apparent Sidereal Time ( GAST) will not, and accordingly your Greenwhich Hour Angle will not, as well as in a lesser extend your Declination.

    So, you would have to perform 2 different calculations : a first one with the correct TT (your precepts just indicated) from which you keep RA and D, and a second one with the correct UT from which you keep just GAST, and subsequently combine RA and GAST to get GHA. The GHA "automatic computation feature" is no longer here.

    This is why if delta T is incorrect, you must have a way to fully independently change it without having to do it through changing UT.

    Please let somebody (George ? Frank ?) correct me if I am wrong, but I thinhk this is exactly the way results would behave.

    Best Regards to all

    Antoine M. "Kermit" Couëtte

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