Air molecules scatter shorter visible wavelengths more strongly. The light scattered towards your eyes makes the daytime sky look blue.
White light carries many colours
Sunlight includes a range of visible wavelengths. As it passes through the atmosphere, it interacts with gases and particles. Some light continues on its path and some is scattered in other directions, reaching your eyes from across the sky.
Small molecules, a visible effect
For molecules much smaller than visible wavelengths, Rayleigh scattering is much stronger at shorter wavelengths. In the idealised model, scattering strength varies inversely with the fourth power of wavelength. This helps explain why blue light is scattered more strongly than red light.
Then why is a sunset different?
When the Sun is low, its light travels through a longer atmospheric path. More of the shorter-wavelength light is scattered out of the direct beam, and the remaining light can look warmer. Clouds, aerosols, and other conditions affect the colours you actually see.
A safe observation
Compare the colour overhead and near the horizon at different times, looking away from the Sun. Write down the weather and cloud cover. Never look directly at the Sun or use binoculars to observe it. A simple sky journal turns a familiar scene into a question you can revisit.
Sources & further reading
This founding-edition article was drafted with AI assistance and checked against the sources above. It has not had independent expert review. Read our editorial approach.
