The selenite is, in fact, a doubly refracting crystal, and the positions in question are those in which the plane of vibration of the ordinary ray coincides with that of the polariser (or analyser ...
The phenomenon is caused by the refraction of moonlight from ice crystals in the upper atmosphere. According to the Met Office, the halo can mean rainfall might be approaching. It added ...
The phenomenon is caused by the refraction of moonlight through ice crystals in the upper atmosphere According to the Met Office, the halo could mean rainfall is on the way. The Met Office ...