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    Re: Pub.249 Epoch 2020 is available.
    From: Brad Morris
    Date: 2018 Nov 3, 18:02 -0700


    This is a fact:  HO249, v1 provides the computed altitude to the nearest minute and true azimuth to nearest degree for the seven best stars suitable for a fix from any latitude and any local hour angle of Aires. I do hope I haven't screwed that up badly :)

    This is discussion: The issue is that you, Rafal, wish to publish the computed altitude data to 0.1'. At this level of precision, you must account for aberration and nutation.  You can safely ignore the Chandler Wobble, its amplitude will not affect your tabular data.  Aberration, with a period of one year, has an amplitude of 0.5'.  Nutation, with a period of 18.6 years, has an amplitude of 0.15'.  This means you CANNOT publish once every 5 years (or so) like HO249 but must publish monthly in order to capture these affects.  With a "Monthly HO249,v1", you can have data to 0.1' as the precomputed altitude will be correct.  

    If you, Rafal, expect the navigator to produce the SHA and declination from an independent source such as the Nautical Almanac, then you aren't recreating HO249.  You are creating something else, because the star's position (computed altitude and azimuth) are already included in the real HO249.  

    Perhaps we should slow down a bit.  I can tell you are proud about your table and that is good!  I am just having trouble understanding what you are doing, okay?


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