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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,
> 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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