Atmospheric
Optics
Pillars, Sundogs & Windows
Orion Elenzil saw this between Seattle and San Francisco.
A very tall (17�) and bright sun pillar dominates the high altitude sky.
Prismatic sundogs accompany the low sun. Their upwards �extensions� are weak 22 degree halo fragments.
Something is odd about the 'reflections' along the wing.
Image ©Orion Elenzil, shown with permission
Robert Greenler first conceived of column crystals creating pillars in the early 1970s. He and his student proved the idea with their pioneer computer ray tracing.
Column crystals drift with their long axis horizontal. The axis can, of course, point in any compass direction. Millions of crystals have all rotation positions around the long axis just as if they were actually spinning.
Improbable circumstances for creating a pillar? We need near horizontal facets to mirror the sun.
But look at the diagram. The yellow arrow is the direction perpendicular to a crystal prism face. Where does it point?
To find out, OPOD's computer spun a crystal around its long axis while also pointing it in random compass directions.
The black dots on the sky sphere mark the directions of the yellow arrow.
Surprisingly, the dots do not spread randomly over the sphere. They cluster strongly at the north pole. The crystal side facets spend much of their time nearly horizontal.
Just what we need to create a sun pillar!
Wobbly plate crystals make most pillars. Their near horizontal facets reflect the sun towards the eye to create the illusion of an upward shaft of light.
But perhaps there were not enough plate crystals. Plates make sundogs and the latter are weak. The pillar is also tall for a sun still a few degrees above the horizon.
Column crystals could have made the pillar rather than plates. They make tall pillars when the sun is above the horizon.
How can horizontal columns make a pillar when their facets tilt in all directions? See right...
Wing reflections?
The pillar and bright horizon appear three times along the wing. They are created by reflections inside the triple aircraft window rather than by the wing surface. Double and triple glazed windows create many illusions.
