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    Re: No Lunars Era
    From: Frank Reed CT
    Date: 2004 Dec 6, 19:47 EST
    Alex E wrote:
    "As I understand the story, L&C were specially taught by the best available teachers how to do lunars."
    I don't think that's accurate. They had an instructor with a high-status title. Titles do not make good teachers. I think Thomas Jefferson deserves a fair share of the blame for all of this. He was far too personally involved in details of the expedition and even in lunar observations themselves. If you hit the Library of Congress web site and search the Jefferson papers, you will find numerous letters to/from TJ on the topic of lunars and other methods of determining longitude.
    Imagine how differently the expedition's mapping efforts would have turned out if they had simply sent a competent ocean-going navigator with knowledge of lunars...

    "Still they:
    a) did not understand that it is desirable to take altitudes
    (even for the simple reason that taking altitudes reduces
    the amount of calculations). I do not accept the argument that
    "they had other more important things to do". Look how many
    sights they took!"
    They were advised NOT to take altitudes because those could be calculated later from the watch time. Yes, this was a mistake. As Ken M has pointed out, because they did not do complete observations and computations, they missed an important opportunity to validate their observations.
    And wrote:
    "From my point of view this story demontrates that the method was
    too complicated for an average XIX century mariner."
    This just isn't true. The majority of 19th century students of navigation learned how to do lunars and presumably had no serious difficult with them. But in practice they proved to be of somewhat limited value. By the way, as far as the math is concerned, working a time sight by the standard method in Bowditch involves almost EXACTLY the same mathematical steps as working a lunar. For a lunar the total calculation is about three times as long as a time sight, but no more difficult. Note that time sight calculations were done on a daily basis on almost every ship at sea from about 1840 through the end of the century. The math was not the problem.

    Ken M wrote:
    > I've done quite a few lunars using only an almanac, log tables, and pencil
    > & paper (using old methods such as Witchell's and Maskelyne's for clearing
    > the distance). It usually takes me 45-60 minutes from start to finish
    > (including the lunar sights, but not a time sight).
    And Alex E replied:
    "This does not disprove my opinion stated above:-)
    My undergraduates can solve some problems that puzzled Euler
    or Archimedes:-)"
    True enough, but regardless, the math was not the issue.

    And concluded:
    "P.S. 1828 Norie is especially interesting to me, not only because of
    navigation, but also from the point of view of my main profession:
    mathematical education. "
    Yes, it's very interesting to see how much things have changed. You should take a look at the opening pages of Bowditch's appendix on occultations and eclipses. He explains that the calculations are easier if you know how to use + and - signs on numbers, as in algebra, and then gives a little tutorial on the topic.
    Frank R
    [ ] Mystic, Connecticut
    [X] Chicago, Illinois
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