What is a 'solar pillar'?

A solar pillar is an atmospheric effect which results in a vertical band of light stretching from the Sun near the horizon, almost all the way to your local zenith. As with other atmospheric optical effects, the root cause is usually in the detailed shapes of the ice crystals refracting the sunlight, and this is a complex subject for which I am ill equipped to speak.

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All answers are provided by Dr. Sten Odenwald (Raytheon STX) for the
NASA IMAGE/POETRY Education and Public Outreach program.