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    Refraction
    From: Gary LaPook
    Date: 2007 Nov 09, 02:09 -0800

    Gary LaPook writes:
    
    Back in March there was a discussion of various formulas to use to
    predict refraction. I have found some other formulas that may be more
    precise. The U.S. Naval Observatory used to publish its "Almanac For
    computers" but stopped it after 1991. That publication has several
    formulas for refraction:
    
    (1)     R' = cot(a + (7.31/(a + 4.4)))
    
    (2)    R = R' - 0.06sin(14.7R' + 13)
    
    
    R is in minutes and a is the observed altitude. "At sea level, with
    air temperature of 10�C and pressure of 1010 mb, R' of eq. (1) is
    accurate to 0.07' and R of eq. (2) is accurate to 0.015' for an
    altitude range of 0� - 90�."
    
    
    "For nonstandard conditions the following formula is accurate to about
    0.2' for temperatures in the range of -20� to + 40� C and pressures of
    970 - 1050 mb.
    
    (3)   R = R'((P - 80)/930)/(1 + 8x10 ^ -5(R' + 39) T - 10)))
    
    
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