The sky appears blue due to a phenomenon called Rayleigh scattering. When sunlight travels through the Earth’s atmosphere, it collides with gas molecules. These molecules scatter the light in all directions, but they scatter shorter wavelengths (blue light) more strongly than longer wavelengths (red light).
This selective scattering means that when we look at the sky, we see predominantly blue light that has been scattered by atmospheric gases. The process is similar to how:
- Blue light is scattered about 10 times more than red light
- The scattered blue light reaches our eyes from all directions in the sky
- Without an atmosphere, the sky would appear black, as it does in space