The sky looks blue because sunlight gets scattered by the air, and the shorter, bluer wavelengths are scattered much more strongly than the red ones as light passes through the atmosphere.

Simple explanation

  • Sunlight is actually a mix of many colors, even though it looks white.
  • As this light enters Earth’s atmosphere, tiny gas molecules (mostly nitrogen and oxygen) scatter the light in all directions.
  • Short‑wavelength colors like violet and blue get scattered far more efficiently than longer‑wavelength colors like red and orange (this is called Rayleigh scattering).

Because that scattered blue light is sent toward your eyes from all over the sky, the whole dome of the sky appears blue most of the time.

Why blue and not violet?

  • The sun emits a bit more blue than violet, so there is more blue light available to scatter.
  • Human eyes are less sensitive to violet than to blue, so our brains interpret the scattered light as predominantly blue rather than purple.

What about sunsets and sunrises?

  • When the sun is low on the horizon, sunlight has to travel through a thicker layer of atmosphere.
  • Along that longer path, much of the blue light has already been scattered out of the direct beam, so the remaining direct light is richer in reds and oranges, making sunsets and sunrises look dramatic and reddish.

Quick forum-style takeaway

The sky is blue mainly because gas molecules in the atmosphere scatter short‑wavelength blue light in all directions much more than other colors, and our eyes are tuned to see that scattered blue best.

Information gathered from public forums or data available on the internet and portrayed here.