Question: Why is the sky blue?

Keywords: ,

  1. It is due to something called “Rayleigh scattering” It has a formula, but basically says that molecules can randomly scatter light particles that bounce off them, and short wavelength light (blue) is *much* more likely to be scattered than long wavelength light (red).

    So. White light from the sun passes through the atmosphere above our heads. Because of Rayleigh scattering, some of the blue light is scattered into different directions, and some of it ends up coming straight down – and we see that as the sky being blue.

    However – the red light keeps on going mostly straight. This is why we see red skies at sunset – the light from the sun has to travel through a *lot* of atmosphere to get to us. Most of the blue light is deflected elsewhere – but the red light is only deflected a little bit.

    UPDATE – good point from Simon. Big volcano eruptions are a great source of amazing sunsets :).


  2. Matthew has answered this very well, but I’ll just add that sunsets are often even redder or pinker if there is some kind of pollution in the atmosphere.


  3. Nice answer! Nothing to add.


  4. good answers above