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    Re: Lunar Distances: Graphic Methods
    From: Henry Halboth
    Date: 2004 Apr 23, 23:19 -0400

    It was not my intent to advocate any method of solution as respects any
    navigational problem, but rather to invite attention to devices of the
    past, of which there were enough to fill any number of scrap bins. There
    have been enough methods of solution to satisfy most any taste in
    celestial navigation, however, in the final analysis, practical skill in
    use of the sextant, or whatever, becomes the governing factor, whether it
    be in measurement of altitude, lunar distance, horizontal angle, or
    otherwise, as no method will correct for a bad observation. I seem to
    remember it having been Bowditch's intent to reduce the mathematics of
    navigation to the understanding of every seaman aboard his ship -
    including the cook - although I do question his success rate. I also was
    not aware that we were going to start a thread on lifeboat navigation, on
    the subject of which I may have a few earthy comments - my sextant box is
    still fitted for backpacking while going down a manrope in a heavy sea.
    
    On Fri, 23 Apr 2004 13:48:05 EDT Frank Reed  writes:
    > Henry H wrote:
    > "This system used a plastic coated globe and finely calibrated,
    > vernier
    > equipped arcs
    > for plotting; the idea being that Zenith Distances swung from
    > carefully
    > plotted Geographical Coordinates of observed celestial bodies would
    > be used in
    > position determination - accuracy obviously being proportionate to
    > sphere size and
    > instrument accuracy."
    >
    > It seems to me that the problem with these physical spheres is that
    > they are
    > not easier to use than standard sight reduction tables. They solve a
    > problem
    > which is already solved. And in addition, they take up space, and
    > they don't
    > translate too well to lifeboat navigation.
    >
    > And:
    > "Obviously, the system never really caught on from a practical point
    > of view
    > but, in retrospect, it appears potentially usable for Lunar
    > Calculations."
    >
    > Honestly, I think a sphere would be even less appropriate for
    > lunars. You
    > need to do lunars calculations at an accuracy that is from 3 to 10
    > times better
    > than standard celestial altitude sights. That would imply a sphere
    > which is
    > either proportionately bigger or proportionately more accurate in
    > its
    > manufacture. Either option would make the thing expensive and
    > unwieldy. Also, as with the
    > standard altitude problem, a system like this solves a problem which
    > is
    > already solved. There are endless methods for solving lunars and
    > most of them are
    > efficient and not especially difficult to use (after you get past
    > the initial
    > learning curve). A typical lunars calculation in the 19th century
    > was not
    > especially more difficult than a standard time sight calculation.
    > Both would
    > require about half of a standard sheet of paper. The difficulty of
    > lunars
    > calculations was greatly exaggerated in the 20th century. This is
    > probably a reflection
    > of the "bad taste" left with the last generation of navigation
    > students who
    > had to learn lunars for (what seemed to them) no reason at all.
    >
    > Frank E. Reed
    > [ ] Mystic, Connecticut
    > [X] Chicago, Illinois
    
    
    

       
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