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   Pyramidal Crystal Parhelia 

  


Parhelia of oriented pyramidal crystals.


When ice crystals take shapes similar to that shown they can be oriented and then produce exotic 'parhelia' very unlike the familiar sundogs of ordinary plate crystals.

The display at left has crystal tilts of 1 (std deviation) and they create many odd parhelia.

Rather poor crystal orientations can still produce parhelia arcs. The crystals in the display at right had their tilts increased to 15 at right yet some parhelion arcs survive, particularly the extremely bright and colourful 23° 'upper parhelion' above the sun.

The pyramidal parhelia are named after the equivalent circular halo ray path but, like ordinary sundogs, they are not necessarily at that distance from the sun. Thus, the uppermost arc is a 23 parhelion but it lies above the 23 circular halo and its distance depends on the solar elevation.

Simulation: sun centered fisheye with the sun 30 high.  50% of crystals were randomly oriented in order to produce the 9,18 and 23 circular halos.