The phenomenon that explains why the sky appears blue is called Rayleigh scattering. This occurs when sunlight passes through the atmosphere and is scattered by air molecules. Shorter wavelengths of light, such as blue light, scatter more than longer wavelengths like red light. As a result, when we look up at the sky during the day, we see more blue light scattered in all directions. This scattering effect is more pronounced when the sun is higher, giving the sky its characteristic blue appearance.