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    Re: Night moon sights
    From: Trevor Kenchington
    Date: 2004 Feb 1, 08:37 +0000

    Peter Fogg wrote:
    > All agree that there is a false horizon line, where the moon's
    > relected light is cut off, some way between the real horizon and the
    > point of observation.
    Provided that the Moon's altitude is high enough. For any given sea
    state and height of eye, there must be some altitude below which rays of
    light from the Moon strike the observer's horizon and there reflect to
    his eye.
    Presumably, it is when the Moon is below that altitude that the
    irradiation effect becomes important and the false horizon rises above
    the real horizon. At a guess, small boats and high latitudes tend to
    make for reflected light reaching to the true horizon and hence a raised
    false horizon while large heights of eye and low latitudes tend to give
    the reverse -- though I have never attempted a sextant sight under
    either set of conditions, so this is purely theoretical for my part.
    Trevor J. Kenchington PhD                         Gadus@iStar.ca
    Gadus Associates,                                 Office(902) 889-9250
    R.R.#1, Musquodoboit Harbour,                     Fax   (902) 889-9251
    Nova Scotia  B0J 2L0, CANADA                      Home  (902) 889-3555
                         Science Serving the Fisheries

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