|Lunar Elliptical Halo
Small compared to the 22° halo, often faint and fleeting, rare, mysterious, supposedly and improbably made by unphysical crystals.
Images captured by Michael Busse at Hannover, Germany on March 27, '13.
Images ©Michael Busse, shown with permission
The general behaviour of ellipticals, their variation with sun/moon altitude and their several rings, can be explained by invoking crystals like these. However, the devil is in the details and they are not well explained.