Q. Why is the sky blue?

A. Sky appears blue because blue light is what our eyes see. Light exhibits the characteristics of a wave and the color of light is determined by the length of the wave. For example, red light has a long wavelength while blue light has a short wavelength. By the way, light that includes all the colors is transparent and that is why the color of the light from the sun is actually transparent. When the light of the sun reaches the earth, it hits our atmosphere, including dust in the air, and its direction becomes scattered. Blue light with a shorter wave length scatters more easily in the atmosphere and thus the sky looks blue. In contrast to the middle of the day, sunlight shines diagonally from a greater distance and through a thicker layer of the atmosphere at sunrise and sunset. With the greater distance through the atmosphere, the scattered blue light does not reach our eyes as readily as the longer wavelength red light, which reaches our eyes in a direct line with little scattering. As a result, the rising and setting sun looks reddish.