Quote:
Originally Posted by David Tollefson
.......* make up and answer at least one additional question. Why is the sky blue? Well, actually, the sky is NOT blue, that is just a function of the light emitance of the gasses that make up our atmosphere......
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Actually Dave, the sky is not blue to the emittance of gasses but due to Rayleigh (elastic) scattering of photons by molecules in the atmosphere. Rayleigh scattering depends on the inverse fourth power of the wavelength - a very strong dependence. Sunlight covers the range of wavelengths in the visible spectrum, from short wavelengths at the violet-blue end to long wavelengths at the red end. The violet-blue-green photons are more strongly scattered than those at the red-orange-yellow end, so the sky appears to be blueish.
The photons are never really absorbed by the molecules, so they are not 'emitted'. Elastic scattering means the wavelength of the light is not changed in the scattering process.