Definition
For a path length through the atmosphere, for solar radiation incident at angle relative to the normal to the Earth's surface, the air mass coefficient is:
-
(A.1)
where is the zenith path length (i.e. normal to the Earth's surface) at sea level and is the zenith angle in degrees.
The air mass number is thus dependent on the Sun's elevation path through the sky and therefore varies with time of day and with the passing seasons of the year, and with the latitude of the observer.
Read more about this topic: Air Mass (solar Energy)
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