The sky appears blue because of a phenomenon called Rayleigh scattering. When sunlight reaches Earth’s atmosphere, it consists of a spectrum of colors, just like a rainbow. This sunlight encounters tiny molecules of nitrogen and oxygen in the atmosphere, which are much smaller than the wavelength of visible light.

Rayleigh scattering occurs when light particles (photons) interact with these small molecules. Shorter wavelengths of light, such as blue and violet, scatter more easily and in all directions when they bump into the gas molecules. However, since our eyes are more sensitive to blue light than violet, the sky appears blue to us.

The other colors of the spectrum are also scattered, but not as much. Red light, for instance, has a longer wavelength and is scattered less by the atmosphere. This is why, during sunrise and sunset, when sunlight travels a longer path through the atmosphere, blue light gets scattered away almost entirely, and red and orange hues dominate the sky, giving us beautiful sunrises and sunsets.

In summary, the blue color of the sky is a result of the preferential scattering of blue light by Earth’s atmosphere.