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    Re: sextants on aeroplanes
    From: Jeremy C
    Date: 2008 Dec 13, 04:58 EST
    Sextants and quadrants allow a greater
    range of measurement which might be useful for lunar distance
    measurements, horizontal sextant angles for coast wise navigation and in
    the rare case of a body within 30º of the zenith with an obstructed
    horizon below it but a clear horizon in the opposite direction in which
    case the navigator could turn his back to the star and use the opposing
    horizon for the sight. (I don't know if this was ever actually done in
    real life.)
    This has been done in practice at sea.  I have done it several times in the tropics when the sun is high.  Typically because at the regular azimuth there is a thunderstorm that obscures or muddles the true horizon but there is a perfectly good horizon 180 degrees out.  Shoot a backsight, and you are good to go; as long as you remember how to do it.  It is also in the US Coast Guard tests, but mostly as Hs to Ho reductions.

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