Why the sky is blue, explained properly

Written for UpdateSee: the essentials, without the noise.

Sunlight contains every colour, and as it passes through the atmosphere the gas molecules scatter the shorter blue wavelengths far more than the longer red ones. Looking anywhere but directly at the sun, you see that scattered blue light arriving from every direction. The effect is called Rayleigh scattering, and it is stronger the shorter the wavelength.

Sunlight contains every colour, and as it passes through the atmosphere the gas molecules scatter the shorter blue wavelengths far more than the longer red ones.

The same physics explains sunsets. When the sun is low, its light travels through much more air, most of the blue is scattered away before it reaches you, and the remaining light leans orange and red. Dust and smoke deepen the colours, which is why evenings after a distant wildfire or a volcanic eruption can look so dramatic.