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    Re: Lunar Distance in Wikipedia
    From: Frank Reed
    Date: 2007 Sep 16, 23:47 -0400

    George, you wrote:
    "I now have an authoritative answer from "the horse's mouth", to wit,
    Catherine Hohenkerk of HM Nautical Almanac Office"
    Consider tossing a grain of salt in that horse's mouth, George. The present
    NAO is a vestigial remnant of its former self.
    And also:
    "That is in accord with the date that was given by D. Sadler, and qoted by
    (I think) Frank Reed. Sadler was Superintendent of the NAO, so as Catherine
    says, he ought to know."
    I don't think I referenced D.H. Sadler as a source, and I wouldn't trust him
    without double-checking on matters like lunar distances which were
    peripheral to his expertise. But this tidbit from Hohenkerk does tell us
    something relevant: her source is probably none other than that little
    booklet "Man is not Lost" which lists Sadler as the principal author. The
    information on dates in there is somewhat contradictory. The dates which I
    previously posted in a message titled "Some Nautical Almanac history (part
    I)" were checked, for the most part, by going to the almanacs themselves.
    And that's the correct citation (e.g., "Nautical Almanac 1906" is the source
    if you're saying something about the contents of that volume).
    Here's a specific example of my slight caution with respect to Sadler's
    writings on lunars:
    In "Man is not Lost", he wrote, "it took three hours to reduce a lunar
    distance in 1800". This is a myth, plain and simple. It has been repeated
    many times since including, I think, in Sobel's "Longtude". It apparently
    arose from a letter published in the Philosophical Transactions *before* the
    first publication of the Nautical Almanac in which several navigators who
    had sailed to the East Indies using lunars explained that clearing lunars
    "only" took three (or four?) hours. But *after* the beginning of the annual
    publication of the Nautical Almanac in 1767, the vast majority of the work,
    which consisted of calculating the Moon's true position, was eliminated (it
    was done in advance by Maskelyne's human computers). By 1800, there were
    many practical methods for clearing lunars available which reduced the total
    time for the calculation (from beginning to end, including calculating local
    apparent time) to twenty minutes or even less. The fact that Sadler gets
    this basic fact wrong tells me that he was interested in the topic of lunar
    distances at a somewhat superificial level. If he had ever tried clearing a
    lunar using one of the methods available in 1800, he would have known
    By the way, I should emphasize that the dates you got from Hohenkerk are
    correct, and they agree with the dates which I listed previously. The only
    detail missing is that the appendix for calculating them (after the full
    tables were dropped) was eliminated from the astronomer's almanac, known as
    "THE Nautical Almanac", in 1919 while the mariner's almanac, the Abridged
    Nautical Almanac, carried them until 1924. And it's worth remembering that
    these dates tell us very little about the practice of celestial navigation.
    It's interesting trivia, of course (if you like navigational trivia --and I
    do), but there were quite a few almanacs available to mariners, both
    government issue and privately published, from various countries. The tables
    were dropped generally in the period from 1905 to 1920. Brief instructions
    in appendices lasted into the 1920s and 1930s. But actual practical use of
    lunar distances had tailed off by the 1850s with some rare examples,
    especially among land surveyors and explorers, after that.
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