blue sky

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The colour of the sky arises from Rayleigh scattering of incident radiation from the Sun by gaseous molecules (primarily nitrogen and oxygen) in the atmosphere. Scattering is strongly wavelength dependent: the short wavelengths of blue and violet light are strongly deflected, whereas the longer-wavelength red, orange, and yellow are largely unaffected. Blue light reaching an observer has been subject to multiple scattering and is therefore classed as diffuse radiation. In the absence of larger solid particles or water droplets, the blue is intense, but when they are present, Mie scattering of longer wavelengths introduces white light, causing a paler tint of blue.

Subjects: Meteorology and Climatology.

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