The blue color of the sky is primarily due to a phenomenon called Rayleigh scattering. Here’s how it works:

1. Sunlight, which appears white, is composed of a spectrum of colors, including all the colors of the rainbow.
2. As sunlight enters Earth’s atmosphere, it contains a mixture of different wavelengths of light. Shorter wavelengths, like blue and violet, are scattered more effectively by the molecules and particles in the atmosphere.
3. The shorter blue wavelengths are scattered in all directions by the gases and tiny particles in the atmosphere. This scattering causes the blue light to spread out in every direction, making the sky appear blue to an observer on the Earth’s surface.
4. Other colors, like red and orange, have longer wavelengths and are scattered less by the atmosphere. As a result, they tend to pass through the atmosphere more directly, which is why we see them more prominently during sunrise and sunset when the sunlight has to pass through more of the Earth’s atmosphere.

So, in a nutshell, the sky appears blue because shorter blue wavelengths of sunlight are scattered in all directions by the atmosphere, making blue the predominant color we see when we look up during the day.