Is the Sky really purple? Scientifcly!?

Question

Is the Sky really purple? Scientifcly!?

Answer 1

No!

The sky is black (colorless) at night and blue during the day if it is cloudless and grey if it is cloudy. It is occasionally green when tornadic storms are around (due to ice crystals in the clouds.

The sky appears blue during the day for two reasons. The main one is that light from the sun is scattering by atoms and molecules in the atmosphere.

Light scattering by particles depends on the relative "sizes" of the photons and the particles.

In the case of visible light, molecules are much smaller than the wavelength of light, so blue light gets scattered much more than red light.

So as light from the sun enters the atmosphere, more blue photons get reflected (not absorbed) by molecules than red photons - but then the blue photons get reflected again and again until they reach us. So the blue light comes from all over, the red light comes almost straight from the sun.

This is also why the sun looks redder at sunrise and sunset - the light's path through the atmosphere is longer when the sun is on the horizon than when it is high in the sky.

The reason it appears blue and not violet (which is even shorter in wavelength) is that (a) there is less violet light than blue light from the sun; and (b) our eyes are not very sensitive to violet light.

Interaction of light with the atmosphere does all sorts of weird and wonderful things that physics can explain:

http://hyperphysics.phy-astr.gsu.edu/Hba...