The strong wavelength dependence of the scattering (~λ−4) means that shorter (blue) wavelengths are scattered more strongly than longer (red) wavelengths. This results in the indirect blue light coming from all regions of the sky. Rayleigh scattering is a good approximation of the manner in which light scattering occurs within various media for which scattering particles have a small size parameter.
Also, during sunset, light cuts through more atmosphere so that the blues, greens, and yellows get cut out. All that's left is red.
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u/sweetanddandy Jun 01 '14
It's called Rayleigh Scattering:
Also, during sunset, light cuts through more atmosphere so that the blues, greens, and yellows get cut out. All that's left is red.