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    Re: Working a lunar
    From: George Huxtable
    Date: 2007 Sep 20, 17:17 +0100

    Henry Halboth's latest message starts (and I've put his text within quote
    marks to distinguish it from mine)-
    "George and other doubters,"
    and really, I must protest. We have seen many examples of Henry's precision
    in the past, and have no reason AT ALL to doubt his claims!
    "I'm sorry to say that my most recent Lunar effort came out to withing
    4-minutes of Longitude on the first working. As I intimated in my post, this
    degree of accuracy is rather astounding and I am going over all my figures
    to search out any flukes before posting the numbers."
    Henry, don't apologise for something that anyone would be happy to achieve.
    It doesn't require a "fluke" to get such a spot-on answer. It doesn't imply
    that every such measurement, even those made by you, will show similar
    precision, though. The nature of such random scatter is that sometimes, any
    discrepancy will happen to be a small one.
    "George, you are well aware that this is not my first effort, as previous
    posts have spoken of much earlier efforts, before the publishing of
    distances, at least to my knowledge, and the advent of the internet, when I
    found it necessary to calculate the true distances for the time frames
    involved and based on almanac data available."
    What Henry says is quite true, that if you have to calculate lunar distances
    from positions calculated from almanac data for the two bodies, there are so
    many rounding errors in all the corrections that are involved, the accuracy
    gets seriously diluted. In the days when lunar distances were precalculated
    in the almanac, much of that dilution was avoided.
    "My real concern is, that should the accuracy attained in this latest effort
    be repeatable, then the Lunar Distance might well, as far as I am concerned
    at least, become a viable tool for use in emergency situations necessitating
    a recourse to celestial navigation in cases where accurate time be not
    available. This was my original intent in beginning work on Lunars in the
    1940's and early 50's, but as, again to my state of knowledge at the time,
    there were no readily available tabulations of Lunar Distance against GMT,
    discontinued my efforts due to the amount of calculation necessary."
    Well, yes, but if it's going to be of use as an emergency tool, where are
    those precise lunar distance predictions going to come from? That was why I
    asked Henry for the source of the lunar distances he had used. And if it
    comes from some internet source, then I ask whether, at sea, in some
    undefined "emergency situation", such internet data is going to be
    available. If it's possible to print out in advance such predictions, and
    take them to sea, then that would indeed qualify as an "emergency tool" Or
    if Henry can take to sea some computing gadget that predicts such lunar
    distances on the spot from first principles, as is perfectly feasible, then
    lunars could be an emergency tool. But not, surely, if on-line web access is
    called for.
    Going back to the question of a single precise result, what I wanted to
    emphasise was that "one swallow doesn't make a Summer". I wasn't doubting
    any claim  for consistency that Henry had made, because, indeed, he hasn't
    made any such claim, yet. I just wished to qualify any such claim, should
    one be in the offing. I doubt whether Henry, just because his recent lunar
    came out within 4 minutes, is going to claim that therefore 4-minute
    precision is achievable; my warning was made just in case he did.
    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.
    To post to this group, send email to NavList@fer3.com
    To unsubscribe, send email to NavList-unsubscribe@fer3.com

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