Question: Why is the sky blue

Pete Etchells answered on 26 Apr 2012:

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!

The best way to think about it is if you have a big strong friend, and a small weak friend, and they’re trying to get to you through a crowd of people. The big strong friend can barge people out of the way, so they can walk directly to you (they’re the red/yellow light), but the small weak friend gets caught up in the crowd, and gets bounced around a bit before they manage to make it to you from a different direction (so they’re the blue light!).