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    Re: Star-to-star distance for sextant calibration?
    From: Paul Hirose
    Date: 2019 May 21, 22:47 -0700

    On 2019-05-21 15:32, Tony Oz wrote:
    > It's a pity I still cannot get the columns' (φ+D) and (φ-D) meaning...
    
    A couple of us have tried to explain that those columns are probably the
    refraction correction at upper and lower culmination of the star. In my
    previous post the numbers I calculated for Kochab are very close to the
    values in the document. Here are refraction corrections for the Polaris
    to Vega distance at latitude 60, with values from the document in
    parentheses.
    
    Vega (D = 51.6)
    lat = 60
    h = 10, refr. = 4.59' (4.7)
    h = 20, refr. = 2.02' (2.0)
    h = 30, refr. = 1.31' (1.3)
    h = 40, refr. = 1.04' (1.1)
    h = 50, refr. = 0.95' (1.0)
    h = 60, refr. = 0.93' (1.0)
    
    upper culmination 0.94' (1.0)
    lower culmination  5.36' (5.6)
    
    Altitude at lower culmination is only 8.8°, so the discrepancy in
    refraction (T = 10 C and P = 1010 mb) is not surprising.
    

       
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