As has been discussed before in this blog, the sky appears blue because of the scattering of light from the Sun by nitrogen and oxygen molecules. They are small compared to the wavelength of the light and you get Rayleigh scattering
https://en.wikipedia.org/wiki/Rayleigh_scattering#Reason_for_the_blue_color_of_the_sky
This is because the electric field in the light wave excites electrons in the molecules. As they de-excite, a photon is re-radiated but in many directions. If you turn so that your shoulder is lined up with the Sun and twist a polarising filter through 90 degrees, the blue sky goes from light to dark. It is polarised. Compare the sky on the pictures below. The Isle of Man was showing well!
Then I stood with my back to the Sun and repeated the trick. No difference in the sky.
Apparently it is because at 90 degrees to the Sun you are looking at photons sideways on so they will always line up in the same plane. See the animation on this site
https://www.polarization.com/sky/sky.html I will have to think about this because how can we see it if it isn't coming towards us? Or is it polarisation of the waves that don't come to us?
