44° Parhelia

Extremely rare 44-degree parhelia on images of David Bainbridge taken in Northern Minnesota, January 2004. ©David Bainbridge

The halos of interest in this panorama are the coloured 'smudges' on each side of the sun and twice as far from it along the parhelic circle as the sundogs. At first sight they could simply be brighter fragments of the 46� halo but the enlarged lower view shows that they are not. They are closer to the sun.

They are the fabled 44� parhelia. They were previously photographed during the famous Saskatoon display of December 3, 1970 (during which a Kern arc was also reported but not photographed) and purely visual sightings were occasionally reported since.

The 44� parhelia are rare examples of multiple scattering. In effect they are 'sundogs of sundogs' formed by rays that have already passed through a plate crystal - and would otherwise have formed a sundog - intercepting a second plate crystal and being further deflected. The double deflection has a minimum deviation angle of 44�. Very high plate crystal concentrations are needed. As an alternative explanation, peculiar geometries have been invoked to form the parhelia from only the single crystal scattering that normally produces halos.

When observing diamond dust displays with very bright sundogs like this one it is well worth routinely checking - and photographing - the sky twice as far from the sun.

As if 44� parhelia were not enough, the Minnesota images possibly also show 'reflected' Lowitz arcs and 46� contact arcs.