Halo Display, Montana
Imaged by Judy Mosby from Blue Mountain, Missoula, Montana on May 5th '08 ©Judy Mosby, shown with permission.
When water freezes, its molecules become fixed in a precise hexagonal lattice arrangement and this molecular order is manifested on our scale of existence by the shape of ice crystals. Most are hexagonal prisms with flat ends but under some atmospheric conditions pyramidal crystals form - six sided pyramids take the place of the flat ends.
In ordinary ice prisms any two faces are tilted 60 or 90 degrees to each other and sunlight passing between them forms the familiar 22 degree halo and the rare 46°. There are many more possibilities in pyramidal crystals and sunlight filtering through them as they tumble in the sky produces a range of circular halos. This display has 9, 18, 20, 22, 23.8 and a faint but just visible 35 degree radius ring.
The enhanced image show the individual halos more easily. The left-hand has been levels enhanced and unsharp masked in Photoshop. The right-hand has been further enhanced by directional embossing.