why is the sky blue

The blue sky results from Rayleigh scattering, a phenomenon where shorter wavelengths of light, such as blue, are scattered more efficiently by the smaller molecules that make up our atmosphere, like oxygen and nitrogen. Although indigo and violet are actually scattered slightly more than blue, the sun emits more blue light. Additionally, our eyes are more sensitive to blue than to indigo or violet, which is why we perceive the sky as blue rather than any other color 1.

At sunrise and sunset, the longer wavelengths like red, yellow, and orange dominate our view because the light path through the atmosphere is longer, which scatters the shorter blue wavelengths out of sight, leaving the reds and oranges to reach our eyes 2.

On other planets, such as Mars, the atmosphere and its composition result in different sky colors. For instance, the Martian sky appears butterscotch due to iron-rich dust that absorbs blue light 3.