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    Re: Lunar Distances: Graphic Methods
    From: Frank Reed CT
    Date: 2004 Apr 23, 13:48 EDT
    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.

    "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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