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    Re: Any "on line" Star Position Computation available ?
    From: Antoine Couëtte
    Date: 2011 Jun 16, 01:38 -0700

    RE : http://www.fer3.com/arc/m2.aspx?i=116540
    [NavList] Re: Any "on line" Star Position Computation available ?
    From: waldendand---com
    Date: 15 Jun 2011 21:55

    Hello Dave,

    You certainly know all the following information, but - just in case it could help - may I cover an ambiguity which arises quite often as regards Star Catalogs ?

    It has been long recognized that in a number of fields among which Star Catalogs, Astronomers keep using some "linguistic shortcuts" habits well to often.

    Regarding your various quotations from VizieR, it may very well be that the dates quoted for each line might be either :
    - the date of the Geometric Reference Frame only, while the Catalog Epoch might be a different one (a rather unfrequent case), or
    - the date of the Catalog Epoch, while the date of the Geometric Reference Frame might be a different one( e.g. HIPPARCOS 1 or 2 are published for Epoch 1991.25 in Reference Frame 2000.0) , or
    - both dates are similar (e.g. FK5, FK6 are published in a 2000 Reference Frame for Epoch 2000).

    Each Catalog situation is unique and the only way to sort things out is to carefully check individual Catalog documentation. This matter of fact does not generally raise any difficulty for people familiar with Catalogs but for newcomers, and even unfrequent users, these linguistic approximations/shortcuts (if any) need to be fully clarified each time.

    This might be one explanation (among possible others) to the strange situation you are observing.

    Hope it helps,

    Best Regards


    Antoine M. "Kermit" Couëtte

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