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    Re: Refraction at the horizon.
    From: George Huxtable
    Date: 2008 Mar 15, 20:47 -0000

    
    
    Perhaps, in my previous message, I misunderstood the point Bill was making
    when he wrote-
    
    | I think the refraction between the observer and his horizon *does*
    | make a bit of difference in how sunsets are timed.  Specifically, it
    | affects how distant that horizon actually is, and therefore affects
    | the direction of the light-ray that just grazes the ocean surface.
    | How big is this effect?
    
    and I answered-
    
    It's zero. By definition, a light-ray that just grazes the ocean surface has
    only one possible direction; tangential to that surface, and therefore
    horizontal at that point.
    
    =============================
    
    That was not an attempt to be flippant, but now I see what Bill was getting
    at. And yes, it's true that local refraction will shift that horizon point,
    towards the observer or away from him. And so the direction of light from
    out in space, just grazing at that point, will be different also. Bill may
    well have exposed a flaw in my reasoning. I will need to think about it
    further, for a while. Watch this space...
    
    George.
    
    contact George Huxtable at george---.u-net.com
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    
    
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