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    Re: HO 249 Vol 1, epoch 2010, Typo
    From: Dave Walden
    Date: 2010 Aug 5, 17:20 -0700

    > Dave,
    >
    >I agree, but how the heck did you ever notice this? Working on old
    >problems?
    >
    >...
    >
    >Stan

    As have others, I've worked my way through various sight reduction tables often writing spread-sheets to 'reproduce' the tables. I find generating tables a great way to improve my understanding of what's going on. I'm impressed by HO249 vol 1 and finally decided to see it I could generate the 7 best stars for a given Latitude and LHA of Aries. Bowditch explains the 7 are based on 'distribution, magnitude, altitude, and continuity', but I've never found any discussion of the actual algorithm used. (Has anyone?) The attached generates such a selection with variables to control the weighting of distribution, altitude, and magnitude. I have limits on upper and lower allowed altitudes. Continutity is not addressed. (I'm not sure now why I used Excel instead of FORTRAN, but once started, it was a challenge. The attached should probably be considered more of a puzzle than a user friendly, documented code!) I've picked from all 57 navigation stars. HO249 uses fewer.

    With a fixed set of weights, I can usually get 3-4 of the same stars as HO249. By playing, I sometimes can get all 7. I haven't yet done continuity (the same set of stars for a range of LHA values, and as many carry overs as possible from range to range. With that said, I still wonder at times at the HO249 choice.

    Anyone else tried this? (Bennett has a 249-like table listing all stars and a recommended set with limited resolution.)


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