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    Re: Advancing position circles: Huxtable vs. Zevering
    From: George Huxtable
    Date: 2006 Sep 22, 05:46 -0500

    I have to report a boob I made in a recent message, when I set a
    problem for NavList members. Geoffrey Kolbe has been struggling with
    it, and has communicated backstage to tell me about it. Perhaps others
    have been strugging in the same way.

    What I did was to miswrite what should have been GHA of a star, as
    SHA. I had mis-transcribed an exanple I had set to readers of the
    Journal of Navigation. Luckily, in that Journal, I had got it right.

    So here it is; right, I hope, this time.
    | It strikes me that perhaps NavList members might like to tackle the
    | simple test-problem that I set, as follows-
    | 1. An observer, at position P1, measures the altitude of a star S1,
    | (Dec1 = 0, GHA1 = 0), to be 30 degrees.
    | 2. Then he travels due North by 60 nautical miles (= 1 degree), to
    | 3.. From there, he observes another star S2 (then at Dec2 = N 1
    | degree, GHA2 = W 45 degrees) to be at an altitude of 45 degrees.
    | on Earth is he then?
    | and concluded-
    | "I challenge Zevering to apply his procedure to the problem as set
    | above, to provide us with initial and final positions for the
    | observer, the initial altitude of star S1, and the final altitude of
    | star S2."

    Geoffrey also queries why I should be asking for the star altitudes,
    when they were a precondition of the problem. That was simply to
    ensure that after the positions  P1 and P2 are deduced, a back-check
    is made to ensure that the result is correct. The erroneous method,
    that had been proposed and I was countering, would fail such a check.

    Sorry about all that. I do seem to be getting error-prone in my old


    contact George Huxtable at george@huxtable.u-net.com
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.

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