Why is the sky not red

The sky appears blue to us because of a phenomenon called Rayleigh scattering, in which shorter (blue) wavelengths of light are scattered more than longer (red) wavelengths by the tiny molecules of gases in the atmosphere. This is why the sky typically appears blue during the daytime when the sun is overhead.

Although it might seem intuitive for the sky to appear red, given that the sun itself appears yellowish-red, the scattering effect dominates the color we see. The shorter blue wavelengths are scattered in all directions, reaching our eyes from all parts of the sky, while the longer red wavelengths continue to travel in a more direct path to our eyes, appearing more intense near the sun.

Additionally, the Earth's atmosphere contains aerosols and pollutants that can scatter light, but these have a relatively minor impact on the color of the sky compared to the effects of Rayleigh scattering.

In summary, the sky is not red because the shorter blue wavelengths are scattered more than the longer red wavelengths, resulting in the blue hue we see.