Question: why is the sky blue?

Iain Moal answered on 18 Mar 2014:

There is a well know astronomer who one said:
“If a kid ever asks you just why the sky is blue, you look him or her right in the eye and say, “It’s because of quantum effects involving Rayleigh scattering combined with a lack of violet photon receptors in our retinae.””

… which pretty much sums it up. We can see all the colours in the visible spectrum, (the rainbow=. The sun releases all of these colors of light together, which we would see as white. However, when the light travels through the atmosphere, some of it get scattered away. The light at the blue end of the spectrum gets scattered more, so you see blue light from the sky, as this has been scattered and appears to be coming from all directions. This is also why the sun appears yellow, because the blue light has scattered away, so more yellow light is left coming directly from the sun.

This also explains why sunsets are often red, or orange – when the sun is low, the light passes through more of the atomosphere than when it is high, and so the blue and green light is scattered away even more, leaving the orange and red behind for you to see coming from the sun on the horiozon.