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    Re: 1901 May, 22 Lunar example by French Navy Captain Arago
    From: Antoine Couëtte
    Date: 2010 Feb 23, 21:04 -0800

    Re: your post # [NavList 12012] Date: 23 Feb 2010 20:31

    Feb 24, 2009

    Dear Paul,

    Thank you very much for your comprehensive reply, including all references to access SIMBAD and HIPPARCOS, and also - most important to me - your various results about the occultation times derived from our various assumptions made on both altitude and delta T.

    *******

    You also wrote :


    " Tomorrow I will compute the coordinates of kappa Cancri in several
    reference systems (barycentric ICRS, geocentric ICRS, etc.) to help you
    figure out why our coordinates are different."

    *******

    Yes, please do so.

    It will give a further and better opportunity to try understanding why our numbers are so significantly different for the computed k cnc RA.

    First of all, I need to check whether the 2000.0 reference frame k cnc values I am using do agree with yours (thanks to SIMBAD / Hipparcos), and

    Then I also suspect ( RE : my former post # [NavList 11997]Date: 23 Feb 2010 08:50 ) that we might not be using EXACTLY the very same precession values. The ones I am using are derived from part of the 1984 set of constants - only the first order secular part of it, i.e. the T*1 term - with all higher order terms derived from VSOP87. As early as 1983 late Dr. Pierre Bretagnon had fully established that the official 1984 IAU precession Term in T**3 was quite significantly wrong by an amount which would fully account for a difference of 1 " after one century (which is by the way our observed figures difference for the date of Mar 1901). I just need to investigate this in some further detail.
    To help me here, just be so kind as to indicate to me which Precession data set you are currently using in your software (I would be guessing that you might be using our current (is it 2002 ? or rather 2004 ?) IAU recommended values.


    Thank you again Paul for all your most precious help and

    Best Regards

    Antoine M. "Kermit" Couëtte
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