Rayleigh Scattering

Before these days of scientific research funded by bodies with specific outcomes in mind, wealthy, well-educated gentlemen with a quest for knowledge would conduct experiments in their own laboratories and publish the results, come what may. Today this is called ‘blue-sky research’, signifying research done purely for curiosity.

One such gentleman was Essex-born John William Strutt (1842-1919), educated at Cambridge and later known as Lord Rayleigh. Among other projects of his own devising, such as the discovery of the ‘noble’ atmospheric gas Argon, he decided to find out why the sky is blue.  What he discovered is called Rayleigh scattering and it also explains the other colours we see in the sky, as well as having applications in other fields.

Rayleigh won the 1904 Nobel Prize in Physics for isolating Argon, the gas later used in electric light bulbs and arc-welding, but it was three decades earlier that he found that the Sun’s white light splits into its constituent colours when it hits the natural particles in Earth’s atmosphere. The blue, having the shortest wavelength preferred by human optics, scatters the most and is seen above us. As the Sun moves further away, the longer wavelengths of red and orange take over.

(Top images: Lord Rayleigh at pixel.com / Public domain, sunlight wavelengths by Robert A. Rohde at Wikimedia Commons / CC BY-SA 3.0)