Colour of the Sky

          I was once asked a question that why the sky is blue and not violet. I found the answer through internet that it is due to the less sensitiveness of our eyes. Our eyes are not so sensitive to differentiate the colours in the sun light as intensity of the violet vary. And the oxygen molecules in the sky absorb the wavelengths at the edge of the ultraviolet spectrum.

         

          I thought about these reasons for a while, but in the mean time I was also reading about Raman’s effect. And it just so happened, why can't we understand the colour of sky by Raman’s effect? So I gave a try.

         

          But I don’t know whether I am absolutely right or wrong.

Raman’s effect was stated as,

When photons are scattered from an atom or a molecule, most photons are elastically scattered due to Rayleigh scattering, such that the scattered photons have the same energy (frequency and wavelength) as the incident photons.

However, a small fraction of the scattered photons (approximately 1 in 10 million) are scattered by an excitation, with the scattered photons having a frequency different from, and usually lower than, that of the incident photons.

Since atmosphere consists of so many particles, if I consider the sky as a whole the Raman’s scattering effect will not be negligible. And the frequency of the emitted light is lower than the incident photons. So, when the violet light incident on the molecules of the atmosphere due to Raman’s scattering effect the atmosphere will emit light that is of lower frequency of violet. And so the effect of violet becomes the minimum.

         

I am not saying the reason for the sky being blue is only because of Raman’s effect but Raman’s effect is also the one of the reasons for the sky to be blue and not violet.