This is why the sky appears blue and the sun yellow - more of the higher-frequency blue light arrives at the observer via indirect scattered paths and less blue light follows the direct path, giving the sun a yellow tinge. By the time it reaches the Earth's surface, the spectrum is strongly confined between the far infrared and near ultraviolet.Ītmospheric scattering plays a role in removing higher frequencies from direct sunlight and scattering it about the sky. Īs it passes through the atmosphere, sunlight is attenuated by scattering and absorption the more atmosphere through which it passes, the greater the attenuation.Īs the sunlight travels through the atmosphere, chemicals interact with the sunlight and absorb certain wavelengths changing the amount of short-wavelength light reaching the Earth's surface.Ī more active component of this process is water vapor, which results in a wide variety of absorption bands at many wavelengths, while molecular nitrogen, oxygen and carbon dioxide add to this process. The overall intensity of solar radiation is like that of a black body radiator of the same size at about 5,800 K. Solar irradiance spectrum above atmosphere and at surface "AM1.5" is almost universal when characterizing terrestrial power-generating panels.ĭescription The effective temperature, or black body temperature, of the Sun (5777 K) is the temperature a black body of the same size must have to yield the same total emissive power. The air mass coefficient is commonly used to characterize the performance of solar cells under standardized conditions, and is often referred to using the syntax "AM" followed by a number. The air mass coefficient can be used to help characterize the solar spectrum after solar radiation has traveled through the atmosphere. The air mass coefficient defines the direct optical path length through the Earth's atmosphere, expressed as a ratio relative to the path length vertically upwards, i.e.
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