Elliptical Halo

May 19, 2005


Referred by: Michael Ellestad
Summary authors & editors: Michael Ellestad

The photo above showing a rare elliptical halo was taken on February 15, 2005, from southern Ohio. These odd halos are formed by sunlight refracting through a special type of pyramidal crystal that has a gently sloping pyramidal angle. Conventional halo phenomena result from hexagonal crystals in cirrus clouds and are usually observed as arcs or circular rings. This is the first known elliptical halo observation since 1987 -- a few weeks later, another was observed in New Mexico. Most sightings of this unique halo phenomenon have occurred in Finland and Scandinavia. In order for these halos to form, ice crystals must have a plate habit. The shape of the upper and lower radii of these halos vary somewhat with the Sun's elevation.

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