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    Re: Pub.249 Epoch 2020 is available.
    From: Brad Morris
    Date: 2018 Oct 29, 07:31 -0700
    Hello Rafal
    I do believe you are conflating two issues in your approach.
    The two issues are
    1) Accuracy of your tables?
    2) Which stars to publish data for?
    Let's discuss them calmly for a moment
    In terms of the accuracy of your tables, Frank is attempting to determine if the underlying ephemeris data is correct for the date of the table.  All other topics aside, this will be critical for your success.  It doesn't matter which stars you choose or how many decimal digits of accuracy the tables produce if the underlying ephemeris is incorrect.  Only by insuring the proper ephemeris can we be sure that your tables are worthy.
    Which stars to publish is a separate topic all together.  The 57 bright stars (plus Polaris) are a relatively modern tradition, but they do stand out in the sky.  Your approach, selecting three that provide an optimal cocked hat, is interesting but fails on one critical point.  Clouds.  Your selection assumes clear skies at every azimuth.  That simply isn't the case.  If the navigator relies solely upon your tables, one cloud, properly situated will preclude a fix.  Please carefully note that I am not saying your star selection is a bad idea, just that eliminating the publication of alternate stars is a bad idea.  If your tables indicate, for this AP, these are the best three stars to use, then i think that just wonderful, under the assumption that alternate stars are also published.  You could also indicate best alternates for each primary recommendation, and alternates for the alternates.   
    As a side note, HO249 was primarily targeted for aviators.  They never required 0.1' tabular data, as they are normally moving very fast.  If your intention is to provide aeronautical tables, you shouldn't produce 0.1' tabular data.  But that is just my opinion, you are, of course, free to publish your tables in any way you see fit!
    Brad
       
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