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    Re: Refraction at the horizon.
    From: Marcel Tschudin
    Date: 2008 Mar 20, 00:27 +0200

    George asked:
    >
    >  ..But is this true
    >  zenith distance, or is it apparent zenith distance, after the light has been
    >  refracted?
    
    It's ZD at the observer (apparent)
    
    >  And whichever it is, if the plots were made instead in terms of the other
    >  one, and the ratios were computed for constant values of that other angle
    >  intead, would they look any different?
    
    If I understand you here correctly: I always had only one parameter
    changed from the reference case (=100%).
    
    >  ... It's going to be hard to explain the
    >  very different amount of refraction change in response to a 10% increase in
    >  absolute temperature, and to a 10% reduction in pressure, either of which
    
    Yes, I didn't have at that time an idea on how to proceed best in
    order to make the cause visible.
    
    >  should have exactly the same effect on air density.
    
    That's what I also expected from "textbooks".
    
    >  So the question needs to be asked- why the hell not? That may
    >  point to whatever's going wrong.
    
    It doesn't necessarily have to be wrong; it also could be a difficulty
    to imagine the effects of the relevant physical relationships in the
    context of setting up the layers of the atmospheric model. I know I do
    have to get back to this one day ...
    
    Marcel
    
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