Solar Radiation:

The transfer of energy from the sun to Earth across nearly empty space happens primarily by radiation. Radiation occurs without the involvement of a physical substance as the medium. The sun emits many forms of electromagnetic radiation in varying quantities.

About 43% of the total radiant energy emitted from the sun is in the visible (shortwave) parts of the spectrum. The bulk of the remainder lies in the infrared (49%) and ultraviolet section (7%). Less than 1% of solar radiation is emitted as x-rays, gamma rays, and radio waves.

A perfect radiating body emits energy in all possible wavelengths, but the wave energies are not emitted equally in all wavelengths; a spectrum will show a distinct maximum in energy at a particular wavelength depending upon the temperature of the radiating body. As the temperature increases, the maximum radiation occurs at shorter and shorter wavelengths. The hotter the radiating body, the shorter the wavelength of maximum radiation. For example, a very hot metal rod will emit visible radiation and produce a white glow. On cooling, it will emit more of its energy in longer wavelengths and will glow a reddish color. Eventually no light will be given off, but if you place your hand near the rod, the infrared radiation will be detectable as heat.

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References:

UCAR Radiation Activity and Teacher Guide

Columbia University: Yochanan Kushnir lecture on Solar Radiation

NC State University Climate Education for K-12: Radiation

NESTA Windows to the Universe: Solar Radiation at Earth

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