Abstract

The so-called diffraction corona is a series of alternating pink and pale green rings that is occasionally seen around the sun or moon when observed through a thin layer of altocumulus or cirrocumulus clouds.¹ In the standard explanation of this phenomenon, incident light waves are diffracted by the cloud water droplets and the different wavelengths of visible light possess strong diffraction maxima at different scattering angles.² As a result, the diameter of the cloud droplets producing the corona may be estimated from the angular diameters of the corona rings. In addition, the diffraction theory of the corona predicts that the saturation of the colors of the rings produced by monodisperse water droplets is independent of the droplet size.

© 1990 Optical Society of America