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    Re: Iterative Lunar method
    From: Bruce Cutting
    Date: 2019 Feb 27, 09:30 -0700

    Wendel-
    You indicated, you had built software to do your iterative method.  For
    what calculator and in what language  Would you be willing to share the
    software (absolutely commercial purpose here) - the software s the est
    possible description possible.  I have a TI-98 and several other
    programmable calculators.
    
    Thanks!
    
    Bruce
    
    On Mon, February 25, 2019 20:16, Wendel Brunner wrote:
    > Hello Frank,
    > I appreciate your comments. I realize I have much to learn about various
    > ways of clearing the lunar distance and the observations required, and
    > especially the descriptions and methods outlined in older navigation
    > texts when that method of finding Longitude was actually used in
    > practice. Particularly the understanding that one doesn't have to make
    > terribly precise measurements of altitudes to clear the Lunar Distance
    > using many methods. When I started on Lunars in 1992, what I knew about
    > that process came from reading "Carry On, Mr Bowditch" in middle school,
    > some terse references in the modern navigation books I had available, the
    > Hornblower and Jack Aubrey references (fiction, indeed), and especially
    > the Slocum account in "Sailing Alone Around the World". I planned to
    > measure the LD and take a series of altitudes of the sun and moon before
    > and after, and then interpolate. Lacking the Mythical Three Midshipmen,
    > that seemed to be the only way to do it. But when I couldn't get a Lunar
    > altitude during my observation opportunity sailing to Hawaii - and
    > frequently I have found that because of clouds or fog you just can't get
    > an observation- I had to come up with some other method that works. An
    > iterative method is often used for a variety of calculations, from square
    > roots to polynomial solutions, so it was natural to try it for this
    > problem. Iterative methods lend themselves to programmable
    > calculator/computer solutions; I believe the StarPath calculator uses the
    > same approach to calculating Lunars. And while Slocum's account may be
    > just a footnote or less in the body of navigation information on Lunars,
    > his book has had a major impact on inspiring modern sailors. I had heard
    > about Slocum's Lunar feat from my older sailing mentors. After I read
    > that book and in contemplating my own ocean voyage, like many others I
    > wanted to recapitulate some part of Slocum's experience for myself.
    > Sailing single headed through the Straits of Magellan was probably not in
    > the cards for me, but with my celestial skills, I could attempt to
    > emulate Slocum's lunar feat. So that gets to your basic question, "why do
    > you want to do Lunars"? Certainly not to find Longitude. In fact, there
    > is really no practical reason for celestial navigation at all anymore,
    > although I suspect there are many on this forum who would bristle at that
    > suggestion. The apocalyptic lightning strike that fries all the
    > electronics including the spare pocket GPS tucked away in some shielded
    > place seems unlikely. From reading you describe your rich investigation of
    > the manuals and methods, as well as the myths and misconceptions, of how
    > Lunar navigation was developed and taught in the time when it was
    > important for navigation, I would guess that for you one reason is to be
    > able to do Lunars in a way similar to how it was done in the 18th and
    > 19th Centuries, but perhaps better. Or maybe I am just thinking that is
    > what I would like to learn now. For me the reason to do a Lunar is also
    > linked to appreciating how we came to our understanding of the world.
    > While the explorers opened up the oceans, the astronomers expanded the
    > heavens, breaking out of the confining celestial spheres of the
    > earth-centered Ptolemaic theory and into the vast expanse of of the
    > Copernican universe. Kepler, Galileo and Newton clarified the celestial
    > realm, and sailors equipped with crude instruments to use that knowledge
    > headed out into unknown terrestrial oceans-and sometimes came back. There
    > are certainly better ways to get position than a Lunar Distance, or for
    > that matter, quicker ways to cross an ocean than to be blown about in a
    > sailboat. Staring at the dials of a GPS tells precisely where you are,
    > but a carefully worked out Lunar does more- it connects us with our past,
    > with the navigators of the oceans and the mind who puzzled out the
    > heavens and the earth. The GPS tells position, but a Lunar fix reminds
    > you also where you have come from. As Joshua Slocum wrote in 1899,"The
    > work of the Lunarian, although seldom practiced in these days of
    > chronometers, is beautifully edifying and there is nothing in the realm
    > of navigation that lifts one's heart up more in adoration" Wendel Brunner
    >
    >
    > [plain text auto-generated]
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    > http://fer3.com/arc/m2.aspx/Iterative-Lunar-method-Brunner-feb-2019-g44426
    
    

       
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