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    Re: Memory Aid for Marcq St Hilaire Method
    From: Frank Reed
    Date: 2015 Mar 20, 08:36 -0700

    Herbert, you wrote:
    "Here we obviously have another member of the Flat Earth Society."

    Ha ha ha! Herbert, years ago when I first saw this navigation 'ink', I thought of you since, of course, it employs the "flat earth" analogy for the geometry of the sight, which you have found so annoying in the past. For anyone reading along who is unfamiliar with the issue, the big problem with the "flat earth" version of the diagram is that it obscures the simple and critically important fact that the change in angle is linear with the change in distance. On a round earth with the stars at near infinite distance, there's a one-to-one change in distance with altitude: for every degree that the celestial body falls away from the zenith, the observer moves 60 nautical miles away from the GP of that body. It's the same relationship at all altitudes. By contrast in that "flat earth" analogy, the angle changes in a non-linear fashion, mucking up one of the most important properties of celestial navigation.

    Tattoos like this are not literally memory aids, of course, and it would be a very poor navigator --or one who was poorly instructed-- who needed help remembering that when the observed angle is higher the observer has shifted "towards" the GP (the point directly under the celestial body). That's "square one" celestial navigation.

    Frank Reed

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