|MLA Citation:||Bloomfield, Louis A. "Question 636"|
How Everything Works 22 Jan 2018. 22 Jan 2018 <http://howeverythingworks.org/print1.php?QNum=636>.
Rayleigh scattering is extremely inefficient in particles that are much smaller than the wavelength of the light, so that visible light can travel through miles of molecules in the atmosphere before it experiences significant Rayleigh scattering. But blue light has a shorter wavelength than red light and thus experiences Rayleigh scattering more often than red light. As a result, the atmosphere tends to send the blue portion of sunlight off in every direction. Thus when you look at the atmosphere, it appears blue.
A reader (TAC) points out that the above explanation would seem to imply that the sky should appear violet, since violet light scatters more strongly than blue light. But the spectrum of sunlight peaks in the green—sunlight contains more green light than blue light and more blue light than violet light. The sky combines these two effects together (more green light but better scattering of violet light) and acquires an overall blue appearance.