Violet light, with a wavelength about 400 nm , is almost 10 times as likely to be scattered than red light, which has a wavelength of about 700 nm. At noon, when the sun is high in the sky, light from the sun passes through a relatively thin layer of atmosphere, so only a small fraction off the light will be scattered. The sun looks yellow-white because all the colors are represented almost equally. At sunrise or sunset, light from the sun has to pass through much more atmospheres to reach our eyes. Along the way most of the light towards the blue end of the spectrum is scattered in other directions, but much less of the light towards the red end of the spectrum is scattered, making the sun appear to be orange or red.
So why is the sky blue? Again, let’s look at it when the sun is high in the sky. Some of the light of the sun traveling towards other parts of the Earth is scattered towards us by molecules in the atmosphere. Most of this scattered light is light of the blue end of the spectrum, so the sky appears blue.
Why can’t this same argument be applied to clouds? Why do they look white and not blue? It’s because of the size of the water droplets in clouds. The droplets are much larger than the molecules in the atmosphere, and they scatter light of all colors equally. This make them looks white.
