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    Re: More on lunars. was: Re: Exercise #6, Lunars at sea
    From: George Huxtable
    Date: 2008 Jun 3, 18:30 +0100

    In earlier postings, I had expressed several doubts about a passage, in a
    mailing from Frank (5239), in which he said-
    
    "By the way, if you want to think about lunar distance observations
    differently, each lunar generates a line of position, which you could plot
    on a chart just like any other LOP. But unlike standard altitude LOPs, an
    error of 0.1 minutes of arc in a lunar distance observation implies a 6 n.m.
    error in the lunar LOP. One advantage is that you can shoot lunars when the
    horizon is hidden. Cross two lunar LOPs and you get a rough position fix. "
    
    And now, in 5255, he has clarified the matter.
    
    And as a resut, the penny has dropped! I can now understand what that
    passage was all about.
    
    This time, he really DID have me completely confused, so I am pleased that
    he has cleared the matter up.
    
    His reference to a "lunar" or a "lunar distance" was not to using those
    terms as we would normally understand them, to get time. Instead, they were
    observations made at a precisely known GMT, then their use by working
    "backwards" to deduce a position, however imprecisely, from the Moon's
    parallax I don't complain of the use of those terms in that context (they
    did indeed relate to measurement of a lunar distance) but the words called
    for some explanation or qualification, for "the rest of us". Perhaps the
    phrase "think about using lunar distance observations differently" was
    intended to provide a clue.
    
    Anyway, he completely fooled me. I had no notion that he was bringing his
    old hobby-horse out of its stable for another parade.
    
    Yes, it's an amusing notion that could work, at least in theory, were it not
    so limited by its impracticality. Frank only manages to achieve some sort of
    respectabilty by basing its error on an observational precision of 0.1', the
    same as he claims for his own sextant observations: a precision unmatched,
    as far as I know, by any other observer ever.
    
    George.
    
    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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