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dip, dip short, distance off with buildings, etc.

From: Frank Reed (no email)
Date: Thu Jan 05 2006 - 20:44:23 EST

  • Next message: Frank Reed: "Re: Green Flash and Longitude"

    In Bowditch and elsewhere, there are formulas for dip, dip short, Table XV
    for distance based on measured height, maximum visibility distance, etc., and
    they all have various mysterious corrections for "mean refraction". I've got
    this stuff all figured out pretty well now, and it turns out that there is a
    really easy, though somewhat bizarre (!), way of thinking about the effect of
    refraction in terrestrial, or coastal navigation, situations.

    You can calculate dip or the altitude of a tall building peeking up from
    beyond the horizon using straight Euclidean geometry and trigonometry ignoring
    refraction completely. Then to include refraction, you simply change the
    radius of the Earth from R to R/(1-x) where x depends on the temperature gradient
    of the atmosphere. On average it's about 0.15 but it can easily be anywhere
    in the range 0.13 to 0.17 and sometimes it's as low as 0 or as high as 1.0
    (temperature inversions yield higher values of x).

    This works perfectly to derive the equations in Bowditch for dip, dip short,
    Table XV, and apparently everything else where terrestrial refraction is
    involved. Details upon request...

    -FER
    42.0N 87.7W, or 41.4N 72.1W.
    www.HistoricalAtlas.com/lunars

  • Next message: Frank Reed: "Re: Green Flash and Longitude"



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