|Scattering and polarized light|
Description: Rayleigh scattering and polarization due to it. Using polarizing filter one can use polarization of scattered light to enhance certain features of the sky.
The process of scattering of light by a molecule (Rayleigh scattering) is an important physical phenomenon. Instead of thinking of light simply bouncing off the molecule, one should think of scattering as an absorption followed by re-radiation of light.
The probability for the light to be scattered is proportional to the inverse of the wavelength to the fourth power, . This means that the shorter wavelengths (towards blue) get scattered more strongly than the longer wavelengths (towards red).
Rayleigh scattering can explain why the daytime sky looks blue, the sunset looks red and clouds are white. In the afternoon you observe mostly scattered light (blue) and in the evening you see mostly transmitted light (red). The clouds have higher concentration of water and ice droplets. This means that light gets re-scattered many times and all wavelengths get a chance to scatter out of the clouds, adding up to white light.
Another effect that can be explained by light scattering is polarization. When you look at the sky with Polaroid sunglasses it appears darker or brighter from different angles. This is due to the fact that the scattered light is partially polarized. The white light scattered from the clouds is unpolarized, due to the fact that the light scatters randomly, multiple times. The direction of its polarization becomes random and thus the light is unpolarized. This can be useful for making pretty photographs of the sky.
A photographer wants to take a picture of an interesting cloud formation, so she uses a polarizing filter (assume that she is looking at a part of the sky where the blue is totally polarized) to increase the ratio of the clouds' intensity to that of the blue sky.