Why is the sky blue?
Molecules in the atmosphere scatter shorter visible wavelengths more strongly than longer ones. This sends blue light toward us from across the sky; our eyes' sensitivity also shapes the color we see.
- The scientific idea
- Light scattering
- Fields of science
- Physics
How it works
Look at a patch of blue sky away from the Sun. Sunlight reaches your eyes from that direction because molecules in the atmosphere redirect some of it. Shorter visible wavelengths are scattered more strongly by these molecules than longer ones.
Look closer
Blue is therefore prominent in the light arriving from many parts of the sky. Violet scatters strongly too, but our visual sensitivity helps determine the color we perceive. Larger particles behave differently, so molecular scattering is not a universal recipe for the color of every haze or cloud. Scattering spreads light into different directions; refraction describes a different effect, such as a ray bending at a water–air boundary.