The sun shines on Earth. This sunlight is composed of different colors, each of its colors has its own wavelength. Among all of them, the blue-color wavelength is very short. Therefore, when the sun is at its zenith and the sunlight passes through a small layer of the atmosphere, the blue light is the one that reaches us. However, at the end of the day, the sunlight must cross a large atmospheric layer and it is the orange and red colors that reach us. Photo credit: Louis Gentil