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Altitude Correction for Time of Sunrise and Sunset

-- Emad | August 10, 2020

Question:

My question is about the effect of elevation (height above sea level) when calculating the sunset/sunrise … I got two equations … The first one estimates around one minute difference for every 5000 feet above sea level … While the second equation assumes around one minutes for every 150 feet … I need to know which equation is used for a whole city elevation and which one is used for building or mountain elevation ?!!

-- Emad

Answer:

I believe that the formulation provided in the section on “hour angle” in the wikipedia article describing the sunrise equation is correct. Specifically, adding -2.076*sqrt(elevation in metres)/60 the angle which accounts for the finite apparent size of the solar disk and the effect of the Sun’s apparent position due to atmospheric refraction. Note that this correction accounts for situations where the horizon is below as observer who is located on a mountain, for example.

-- Jeff Mangum

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