Why is the sky blue?

The blue color of the sky is caused by Rayleigh scattering.

Sunlight is made of all colors combined—white light.

When sunlight hits Earth’s atmosphere, it encounters tiny gas molecules—mostly nitrogen and oxygen.

These molecules scatter sunlight in all directions, but they do so unevenly:

Shorter wavelengths (blue and violet) scatter much more than longer wavelengths (red, orange).

Our eyes are most sensitive to blue light and less so to violet, plus some violet gets absorbed higher up—so the sky appears blue to us.