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

It can be the faint smudges on an image of an otherwise dazzling halo display are the ones that raise the hairs on the back of your neck.

The 'ordinary' halos on this panorama assembled from three images are two dazzling sundogs (22� parhelia), a bright parhelic circle, an upper sun pillar, a 22� halo and a faint outer 46� circular halo.

The 'smudges' are 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).

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.


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