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    Re: Lunars using Bennett
    From: Frank Reed
    Date: 2008 Jul 04, 05:40 -0400

    George H, you wrote:
    "But let nobody think, no matter how good those observations may be, and how
    precisely they approach the predictions, that he has got very far towards
    understanding how lunar distance NAVIGATION was done."
    
    Wow. Your statement is way over the top. And wrong.
    
    And you wrote:
    "That's a much more complex business, of which measuring the subtended angle
    between the two bodies is no more than a subset (though an important and
    demanding one)."
    
    Nonsense. It is NOT "much more complex." It is, in fact, quite simple.
    
    And you wrote:
    "Yes, indeed you can call such an exercise "measuring a lunar distance";
    after all, that's literally what it is. But don't confuse it with solving
    the problem of discovering where you are when GMT is as yet unknown, which
    is what lunar distance navigation was all about."
    
    I'm sorry, but the confusion here is on your end, George. You have spent
    almost no time observing lunars yourself. Your experience with their history
    comes mostly from Cotter's book and various other muddled modern sources
    like Howe, and also from late 19th/early 20th century textbooks and
    navigation manuals which were published long, long after the period when
    lunars were commonly used at sea. You learned lunars from mediocre sources,
    and it is no wonder that they cause you so much confusion and that you are
    so convinced about their supposed difficulties. YOU have a lot to learn,
    George. And that's the good news.
    
    And you wrote:
    "Solving that problem calls for a different approach, because when the exact
    time is as yet unknown, neither are the exact positions of the bodies in the
    sky. That's why additional observations of the altitudes of the bodies were
    called for; or another technique, that of iteration, might be possible.
    Scheduling of those observations, with respect to the lunar distances, had
    to be done with care."
    
    No. You measure the altitudes before and after. It's easy. This technique
    was widely known even in Maskelyne's early days. Or if you have cheap labor,
    you get three observers and measure simultaneously. Calculating the
    altitudes was a relatively rare activity and considerably more work, but
    straight-forward in principle for any navigator of that period. Land
    navigators (really "mappers") did frequently calculate altitudes. That was
    their "culture" of position finding. Iteration was something that fascinated
    "armchair navigators" (and still does). At sea it was a pointless activity.
    No one would be so woefully lost at sea that their initial estimate of
    longitude required an iteration through the calculation.
    
    And you wrote:
    "Calculating the result, calling for extreme precision, presented many
    pitfalls, as can be seen by the difficulties a recent example has presented
    to this list."
    
    What pitfalls?? Kent has some problems as do all newcomers but that's
    because this topic is ancient history, and he has been working in a vacuum.
    He has had to deal with the issue of developing refraction formulae and
    understanding augmentation, but in the period this was just cookbook stuff.
    It was EVERY BIT as easy as looking up altitude corrections in a modern
    nautical almanac. And now that he has a chance to communicate with other
    folks who know how it all works, I am sure Kent's analyses will soon line up
    with the rest.
    
    And you wrote:
    "It's also worth mentioning the additional difficulties that measurement
    from an unstable platform underfoot, in real sea conditions, presented to
    the sextant observer: difficulties that have sometimes been made light of in
    list-postings."
    
    LOL. Yes, one must fear the dreaded sails!! Please, George, I do hope you're
    not going to start ranting about the sails getting in the way again. The
    difficulties at sea were, first, all the usual difficulties in celestial
    navigation, most importantly it's all useless when it's cloudy. In addition,
    lunars require even better weather than normal celestial navigation. But
    apart from that, your opinions on the physical difficulties at sea are
    armchair speculations. You are, of course, entitled to speculative opinions,
    just like anyone else, but that's all they are.
    
    And you wrote:
    "To several list members, certainly including me, those intellectual aspects
    of lunar distance navigation are of considerable interest, and have given
    rise to much discussion."
    
    And when you finally understand these "intellectual aspects", you will
    recognize that, while they are fun, they scarcely merit the adjective
    "intellectual." This is not rocket science.
    
    And you wrote:
    "Yes, they all have a historical focus: nobody is measuring lunars to
    navigate with any more. In fact, if we admit it, hardly anyone is really
    doing celestial navigation any more. Almost all our discussions concern a
    dead subject. So what?"
    
    Well, of course! And discussing the historical aspects is FASCINATING.
    That's why I, myself, have posted rather extensive analyses of historical
    lunar distance navigation taken from period logbooks. That's why I delve
    into historical details in depth in my numerous talks about lunar distances
    at Mystic Seaport. It is fundamentally a historical subject, and most
    navigation enthusiasts enjoy the historical aspects. But not everybody has
    the same interests. Many people enjoy using lunars today to test themselves
    and their sextants. That's the limit of their interest. Others enjoy
    considering them for actual modern navigation (in other words, lunar LOPs).
    And many people, like me, are interested in all of these things. It's all
    fun.
    
    By the way, you, yourself, have just RECENTLY dismissed Kent's distinctly
    historical, albeit "textbook", approach to getting local apparent time from
    the stars because you say it's easier to do it with GHA from a modern
    almanac. This attitude, eschewing the historical approach, seems to be in
    conflict with this most recent post, asserting that the historical approach
    is the only way to go. You're changing your own rules. And indeed everybody
    has rules for the game which they apply differently at different times. And
    there's no single right way to go about it. Telling people that they're not
    really doing lunars because they're not following your "rules du jour" is a
    bit pointless.
    
     -FER
    
    
    
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