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    Refraction formulas
    From: Henning Umland
    Date: 2000 Sep 28, 7:03 AM

    In addition to Bennett's formula, Meeus quotes Smart's formula:
    
    R['] = 0.9716*tan(90-H) - 0.0011*(tan(90-H))**3
    
    H is stated in degrees.
    
    According to Meeus, the formula gives accurate results between 15� and 90�.
    At 90�, R becomes 0. I checked the formula repeatedly and found that even at
    10� altitude, the results are accurate enough for navigational purposes.
    
    Henning Umland
    h.umland{at}online.de
    www.umland.onlinehome.de
    

       
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