What is the sky blue?

The sky looks blue because Earth’s atmosphere scatters sunlight.

Sunlight contains all visible colors, but shorter wavelengths—especially blue and violet—scatter more easily when they hit air molecules. This is called Rayleigh scattering. Even though violet scatters strongly too, our eyes are more sensitive to blue, and some violet light is absorbed higher in the atmosphere, so we mostly perceive the sky as blue.

At sunrise and sunset, sunlight travels through more atmosphere, so much of the blue light gets scattered away before it reaches your eyes. The remaining direct light looks red, orange, or pink.