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    Re: Pub.249 Epoch 2020 is available.
    From: Rafal O.
    Date: 2018 Oct 24, 23:30 -0700


        I will post it within one or two days. I want to add few things to it. I have it prepared with 0.1' accuracy. However, 1' can be also easily done. Sample for latitude 51°N I attached below. This version contains exactly the same stars' set at the Pub 249. However, Frank's statement "why in the name of all sanity would you regurgitate the same star choices, with numerous errors, found in the original government-issue series? Make better star choices, maybe using the old tables as a starting point." So, in next few days I want to play a little with selecting my own set of stars. The idea is simple: for a selected latitude L and LHA0 I calculate Hc for all known navigational stars. Some of them fall within the selected range (Hcmin, Hcmax). So, from the initial set of N stars I have n0. The same procedure is repeated for LHA1, LHA2, ... The intersection of these sets gives me first n-stars. From these I need to select those that are the best to make LOPs. The best choice is when three stars' azimuth differs by 120°. I want to calculate some order parameter called c.3 = |1/3 Sum(exp(3*i*Zn))|, where i=sqrt(-1). For ideal case (Zn=0, 120, 240) this gives me c.3=1.0. The more Zn differs from the ideal valus the lower c.3 is. For example if I allow (-10°, +10°) sampling around ideal valus c.3 for such 1'000'000 sampling are within the range (0.88, 1.00):

    > summary(c.n);
       Min. 1st Qu.  Median    Mean 3rd Qu.    Max.
     0.8828  0.9547  0.9750  0.9700  0.9893  1.0000

    For (-5°, +5°):

    > summary(c.n);
       Min. 1st Qu.  Median    Mean 3rd Qu.    Max.
     0.9699  0.9886  0.9937  0.9924  0.9973  1.0000

    and for (-15°, +15°):

    > summary(c.n);
       Min. 1st Qu.  Median    Mean 3rd Qu.    Max.
     0.7491  0.8992  0.9440  0.9333  0.9760  1.0000

    I hope that from these n stars I would be able to select three that are best for sights.

    Best regards,

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