Sun Pillar and Sundog

September 15, 2009

20090915 - Sun Pillar and Sundog

Photographer: Aase Berg
Summary Author:
Ole Johan Løkberg; Aase Berg

September 2009 Earth Science Picture of the Day Viewer's Choice

The photo above shows both a sharp Sun pillar (left) and a striking sundog or mock Sun (right) as observed from Rugldalen, Norway. The bitter air on this winter's day was filled with hexagonal ice crystal plates that wobbled slightly around their horizontal position as they fell toward the surface. Sun pillars form when sunlight is reflected from the bottom or, occasionally, the top surface of aligned plate-shaped ice crystals. Sunlight that also passes through the side faces of these plates is refracted in such a way to form a sundog. However, in crystals where the side faces are not all normal to the direction of sunlight (not perfectly oriented), the refracted rays can be reflected from the crystal's top or bottom faces. These inside reflections in effect elongate the normal sundog "spot" into a shaft of light. This sundog's red-yellow color results from the color of the low Sun. Note that the sundog is approximately 22 degrees from the pillar and the unseen solar disk. Could sightings of such sundog pillars possibly be responsible for the "Pillars of Fire" appearing in many historical texts?