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    Re: Refraction:Which formula for Heights below 15°
    From: Paul Hirose
    Date: 2022 May 17, 15:38 -0700

    The Astronomical Almanac has a formula for apparent altitude less than 15°:

R = P [(0.000 02a + 0.0196)a + 0.1594] / [(273 + T)((0.0845a + 0.505)a + 1)]

where R = refraction (degrees), P = pressure (millibars), T =
temperature (C), a = apparent altitude (deg)

https://archive.org/details/binder1_202003/page/n203/mode/2up?view=theater

--
Paul Hirose
sofajpl.com
       
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