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    Re: Moon Horizon
    From: Frank Reed
    Date: 2009 May 12, 13:47 -0700

    Thomas, you wrote:
    "In several works on celnav the authors had stated the bright reflection
    of the moon on oceans surface would obscure the visible horizon at night
    and create a line below it, called moon horizon (at least by some of them)."
    
    Imagine an idealized model of ocean waves as a long row of saucers sitting 
    edge-to-edge extending out to the horizon. Each one has a reflective interior 
    surface so the light from a celestial body can bounce from the right spot in 
    the saucer to the eye of an observer at some height above the waves. Each 
    saucer reflects a spot of light from a slightly different point within it and 
    so altogether we see a "road" of light beneath that celestial body extending 
    out into the distance. But at a certain distance from the observer, not as 
    far as the true horizon, the spot that would reflect light to the observer is 
    hidden behind the lip of the saucer just in front of it. The road would come 
    to an end. This is presumably why the Moon has that false horizon below the 
    true horizon.
    
    Incidentally, I agree with Peter and others who have said that you can still 
    see the true horizon if you look carefully. I find that this is especially 
    true when the sky is a bit hazy. Then you see that bright illuminated road of 
    reflected light below the Moon. It ends at that "moon horizon". Then there's 
    a narrow dark band. And then the somewhat brighter sky above it. The true 
    horizon is the top of the narrow dark band.
    
    -FER
    
    
    
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