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    Re: Lunars
    From: George Huxtable
    Date: 2007 Sep 23, 17:25 +0100

    John Karl has written-
    "Some of you may want to check out my new book, Celestial Navigation in the
    GPS Age, available from, www.celestaire.com  or www.paracay.com .  Among
    other things, it discusses lunar sights using only the same old
    understandable basics of CN, without using tables or approximations -- just
    a hand calculator and the Almanac."
    Well, that's interesting news. It's a long time since a book has appeared
    that treats lunars seriously. I hope some listmember will purchase a copy on
    our behalf and provide us with a review of it.
    However, it's a bit sad to read, from the author of a work that deals with
    lunars, that-
    "I haven't checked the Nav List for some time.... Now I see some discussion
    on Lunar Distance Tables this month."
    Well, discussion on various aspects of lunars has been occurring, frequently
    if sporadically, for a long time, on this list and on its predecessor. It's
    one of its main topics. Somehow I doubt if lunars get discussed in such
    width or depth elsewhere.
    John Karl's name is new to me, as a contributor to this list. I hope he will
    continue to contribute, and we can learn from each other.
    "BTW, in the book I make the observation that the sun-moon distance changes
    about one minute of arc per two minutes of time.  So to do better than
    finding UT to with one minute requires some pretty adroit observing.  And if
    the LD distance were accurate to one minute of arc, the longitude would be
    accurate to only about 30'."
    John, those facts are well-known to those of us who discuss lunars on this
    list; indeed, they underlie most of the discussion on lunars, to the extent
    that they are often left unstated.
    "Doesn't this explain why the  famous British Parliament Prize was for
    determining longitude better than 30' of arc?? "
    The problem, in those days, wasn't confined to the observing. It was the
    total error, in predicting where the Moon should be in the sky, measuring
    where it is in the sky, and calculating out all those corrections, that had
    to kept within 1', to achieve an accuracy in longitude of 30'. At the time
    the longitude prize was claimed, the predictions were to no better than
    about half a minute. That left only half a minute allowable accuracy, in
    observation + correction. A difficult task indeed, with the instruments of
    the day- and even now!
    contact George Huxtable at george---.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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