The physicist Joseph Strutt, 3rd Baron Rayleigh, detailed how light is scattered by particles shorter than its wavelength. This phenomenon, which has taken his name to become known as Rayleigh scattering, is enacted on sunlight as it moves through the gases of Earth's atmosphere. The short wavelengths (those at the blue end of the spectrum) are scattered most effectively, meaning that we see the sky as blue. This is all the more pronounced when the sun is low to the horizon, and its rays are having to travel through a greater distance of atmospheric gases to reach our eyes, which is why sunsets take on the rich colours of red and orange.
Editors. "Lord Rayleigh discusses the blue sky law and sunsets". The Literary Encyclopedia. First published 30 August 2013
[http://www.litencyc.com/php/stopics.php?rec=true&UID=6338, accessed 17 April 2014.]