File:Brocken spectre, Beinn na Cille - geograph.org.uk - 1779469.jpg

English: Brocken spectre, Beinn na Cille The circle of coloured rings is caused by sunlight from directly behind the observer scattering back from the tiny spherical water droplets that make up cloud. The scattering angle depends on the light wavelength (i.e. colour), so the colours are separated. This appears similar to a rainbow, but the mechanism is not quite the same, since raindrops are comparatively large, allowing refraction inside the drop, while cloud droplets are not much bigger than light wavelengths. The smaller the cloud drops, the larger is the angle of the Brocken spectre. Brocken spectres (or glories) can also be seen from aircraft when flying over clouds. Glories are not an unusual sight in the hills if you can arrange the sun behind you and thin cloud below. Student C.T.R. Wilson spent September 1894 at the Ben Nevis Observatory, and was inspired by this phenomenon to experiment with ways of making clouds in the laboratory, which eventually led to a Nobel Prize for his cloud chamber, later used as a vital tool in studying radioactive decay. See 903255 for more on C.T.R. Wilson.