Quételet rings are an interference phenomenon occurring from reflecting surfaces lightly covered by dust or other small particles - for example dust on glass, algae or pollen on still lakes. They are named after the Belgian astronomer, mathematician, statistician and sociologist Lambert Adolphe Jacques Quételet, better known for the invention of the body mass index rather than for the interference phenomenon he described.
Quételet rings appear when some light rays are reflected before being scattered by the dust and others are scattered before being reflected. The two light paths differ slightly, which produces interference effects. Some wavelengths are enhanced, others are washed out resulting in coloured rings.
In contrast to coronae, Quételet rings are not always centred on their brightest spot.
See H. Joachim Schlichting: Farbige Schattensäume im Wasser. In: Physik in unserer Zeit 34/4 (2004), pp. 177-179.
Quételet rings produced by car headlights illuminating a distant window pane. The reflective coating of the glass contributes to the visibility of the phenomenon. Canon Powershot G6, processed with Adobe Photoshop Elements.