Question: Why are clouds white?

Pete Etchells answered on 26 Apr 2012:

Great question! It’s due to a process called ‘Rayleigh scattering’. Basically, when light from the sun enters our atmosphere, it gets scattered by air particles. Different parts of the light spectrum are different strengths – so the red end has more energy than the blue end. That means that the higher energy light doesn’t get scattered in the sky as much as the lower energy light. So when you look at the sun (which emits all colours of light), you’re only seeing the red and yellow parts of the spectrum. Because the blue part is getting scattered more, when you look at a bit of sky that the sun’s not in, you’ll only see the blue part!

Clouds, on the other hand, have particles that are big enough to scatter all light in the spectrum, so they stay white 🙂