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    Re: J S Letcher and Lunars
    From: Frank Reed
    Date: 2021 Sep 9, 07:32 -0700

    David C, you wrote:
    "The author is clearly a fan of lunars, describng a solo voyage without radio and a cheap timepiece. He became concerned about the accuracy of  the timepiece and used a lunar to to satisfy himself that he would make a safe landfall. The chapters dealing with lunars seem quite readable although I haven't read them yet."

    Yes, and one of the reasons I have recommended Letcher's book so many, many times over the years is because it is "quite readable". He writes excellent prose. I have recommended it less often in the past two years since it seems that we have finally run down the former stockpile of near-new copies of the book at low prices. The price you paid (which you mentioned in an earlier post) is good value, but just a few years ago copies were available for around a dozen dollars (USD). That was a typical price for the previous decade. Honestly it was a steal back then!

    And you wrote:
    "I believe that lunars went out of regular use in the 1850s. This is an example of a lunar  in 1963."

    At sea lunars were essentially done and buried by about 1850. Yes, that's one of the key points that I emphasize in my posts and in my workshops. I should emphasize that this is history, not math. There are no theorems overthrown by a single exception in history. And obsolete practices rarely die in any absolute sense. They become much less common but there are always exceptional instances. I have contended in other contexts that you could find someone, somewhere practicing lunars (or at least "messing about" with lunars) in every decade since 1850. And because the usage is exotic in later decades, those rare cases get somewhat exaggerated attention. Joshua Slocum famously shot one lunar on his solo circumnavigation in the 1890s. He bragged about it in his book and after he returned, too. So there's one in that decade. I shot my first lunar in 1979, when I was 16, around the same time I first saw Letcher's book (though I didn't have the opportunity to read it until many years later). A NavList member who has since moved on (name, anyone?) described his experiences shooting lunars during the Second World War. For Letcher, Slocum, and all these other occasional users, lunars were an interesting experiment, a historical recreation experience, and a fascinating challenge, but it doesn't change the fact that the last decade with significant ocean navigation by lunars was 120 years ago.

    Letcher's book is loaded with good practical advice, and even on lunars he has an important thought. What happens if you lose the date? This is much less likely in 2021 than it was in 1963, but it's still worth considering. Suppose you have been caught up in an exhausting sequence of storms. Maybe you're deep in the Southern Ocean somewhere southeast of New Zealand bound for Cape Horn... You fight terrible wind and sleet. Your vessel loses a sail. You battle to avoid capsizing. You get no sleep. Three days go by, and finally the weather clears. But wait... has it been three days? Or two? Or four?! You've lost the date. But you can recover it quickly with a simple observation of the Moon. This can be a genuine "lunar" meaning a lunar distance observation. Or it could be a standard Moon altitude sight. Work it for each possible date, and one (and only one) will make sense. Or if you're observing the Moon at night, you can look at its position among the background stars, and then plot the possible positions for each date on the star chart in the back of the Nautical Almanac or equivalent. The Moon's position, even judged visually without a sextant, will reveal the date.

    You added:
    "Frank you have been scathing of Cotter's explanation of lunars."

    That's right. The chapter on the history of lunars in Cotter's History of Nautical Astronomy is a train wreck (is that the title? I don't have a copy in sight as I type this). Cotter's work was clearly based on "library research". He did little or no primary source research, and that's the fundamental reason that its so awful. It almost couldn't be worse. It is so widly misleading that I recommend actively avoiding it --not "read it with a skeptical eye" but "don't read it all!". It's a seductive book with some useful chapters and very fine typesetting, and for readers who are roped in by that seduction, it's hard to believe that the lunars chapter could be junk. But it's true. The chapter on the history of lunars fries the reader's brain. Stay away! :)

    You asked:
    "How well does Letcher do? Would his  lunar chapters  form a useful "Introduction to Lunars"?  Is it worth my while rto study the pages? A few years ago I tried to become a lunatic but quickly gave up. There seemed to be a zillion methods of clearing the sight when all I wanted was something that was easy and worked."

    Oh, you want something easy? How about an essay called "Easy Lunars" which I originally wrote as a NavList post. I need to compose a new version of this since some tastes and attitudes have changed since I wrote the original 17 years ago. As for Letcher, yes indeed, you could follow his methodology directly. The math he descirbes is an example of a series method, much like the one that I detail in my Easy Lunars essay and quite similar to the Bowditch-Thomson method I teach in my workshops. Letcher's description of practical aspects of lunars is also excellent, both "real" lunars (GMT by lunar distances) and other related "lunar" methods, like longitude by lunar altitudes and finding the date by peeking at the Moon (see above).

    Note also that there is no real comparison between Letcher's contributions on lunars and Cotter's. They're targeting different audiences and they have different goals. Cotter's chapter is like a contribution to a text in mathematics (a poor text). Letcher is writing for navigators.

    So what's the deal with all those hundreds (zillions!) or methods for clearing lunars? Mostly it's an element of the mythology of lunars. Most navigation manuals in the early 19th century, when lunars were still common, included three or four different methods for clearing lunars. They didn't really need to, but it was something they could advertise easily on the title page. It's important to recognize that this was mere algorithm --just variations on the basic principle. There's no call to learn more than one or two methods, and those who did so probably did it for the mathematical challenge. A lunarian could happily survive with just one method of clearing lunars. Also contrary to the mythology there is little advantage of one method over another. The traditional literature talks about "rigorous" versus "approximative", and some players in the lunarian game develop mistaken anxiety or pompous pedantry over these terms. Anyone who tells you that "rigorous" is better than "approximative" in the game of clearing lunars is an amateur putting on airs... so someone who has simply been conned by the jargon.

    Of course I teach a workshop all about the practice and history of lunars, and I have a run of that coming up in November: http://www.reednavigation.com/lunars-class/. It's loaded with detail on this topic that I couldn't cover in a hundred NavList posts. Yes, it costs money to attend. Prices are going up soon, by the way, but the "early bird" price (currently listed on my website in the link here) will be valid through September 30 (UT date).

    Frank Reed
    Clockwork Mapping / ReedNavigation.com
    Conanicut Island USA

       
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