Unusual Lunar Halo

July 27, 2017

Pyramidal Ice Halo DSC_0098

Photographer: Greg Redfern
Summary Authors: Greg Redfern; Jim Foster

Shown above is an unusual lunar halo formed from poorly aligned pyramidal-shaped ice crystals as observed over the skies of Greene County, Virginia on June 4, 2017. A classic 22-degree halo accompanied the Moon most of the night, but when I took one last look around the sky before turning in, I knew I saw something very unusual, certainly a type of halo I had never seen before. Though ordinary halos have angles between crystal faces (plate-shaped or columnar) of either 60 degrees or 90 degrees, the angles between pyramidal faces show more variation, and thus their halo radii vary from 22 degrees. Note that the Moon is actually a waxing gibbous Moon -- a 2-second exposure makes it look full.

Photo Details: Nikon D810a DSLR camera; 14mm; f/2.8 lens; 2 second exposure; ISO 3200.