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    Re: Biruni and the radius of the Earth by dip
    From: Marcel Tschudin
    Date: 2011 Jan 5, 17:17 +0200

    John, you wrote:
    > Both the dip and the refraction are in the 40 arc minute region for a 500 m
    > peak, ....
    Could there be a misunderstanding? From a 500m high peak the horizon
    has a geometrical dip (without refraction) of about 40 moa. The
    refraction increases this geometrical dip by e.g. 6 moa leading to an
    observed dip of e.g. 46 moa. In this case we deal with the
    "terrestrial" refraction which is considerably smaller than the
    "astronomical" refraction since in the "terrestrial" case the length
    of the ray path through the atmosphere is much shorter.
    Marcel
    
    
    
    

       
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