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    Re: Lunars
    From: Frank Reed
    Date: 2007 Sep 24, 00:18 -0400

    Hi John, you wrote:
    "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."
    
    John, I got a look at your book a while back. It's very nice, but I wouldn't
    think the chapter on lunars would be a really critical reason for anyone to
    buy it. It's very good, of course, and for someone who's never heard of
    lunars, it would be an eye-opener. But there's so much other stuff in the
    book, and maybe you would like to describe it for the group?? Just in
    general terms: what's the book's goal, intended audience, any special point
    of view?, maybe a short list of topics covered, topics not covered?
    
    For those of you who attended the Celestial Navigation Weekend at Mystic
    Seaport in June, 2006, you probably met John Karl. He's that guy from
    Wisconsin (hope I got that right) who was quite interested in Herbert
    Prinz's explanation of solving the standard spherical triangle using a
    diagram (a flat, 2d diagram, that is).
    
    And you asked:
    "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'.  Doesn't this explain why the  famous British
    Parliament Prize was for determining longitude better than 30' of arc?? "
    
    Nope. Just a coincidence. The prize rules were set in 1714. That's even
    before the invention of the reflecting octant, which soon led to the
    sextant. In 1714, it was still harder to imagine measuring the lunar
    distance at a sufficiently accurate level for determining a useful
    longitude. Typical latitude measurements using the non-reflecting
    instruments of that era were known to be accurate to roughly +/-10 minutes
    of arc --sometimes better, sometimes worse.
    
     -FER
    
    
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