Why the sky is blue · Pulse Beat

Sunlight looks white but contains all the colours. Air is made of molecules much smaller than the wavelength of light, and they scatter light. This is Rayleigh scattering, and it is far stronger for s

Sunlight looks white but contains all the colours. Air is made of molecules much smaller than the wavelength of light, and they scatter light. This is Rayleigh scattering, and it is far stronger for short wavelengths: blue light is scattered about six times more than red.

So when you look at any part of the sky away from the Sun, you see blue light that has been bounced toward you from all directions.

At sunrise and sunset the light passes through much more air to reach you. Most of the blue has been scattered away on the way, leaving the reds and oranges.

Violet is scattered even more than blue, but the Sun gives out less of it, the upper atmosphere absorbs some, and our eyes are less sensitive to it, so the sky looks blue rather than violet.