Image Credit & Copyright: Rick Stankiewicz. CLICK image for larger view and look below for information and related links.
Have you ever been driving along during sunset just to look in the direction of the Sun to see a tall vertical beam of sunlight apparently shooting up into the sky from the horizon? That’s what’s known as a “Sun Pillar” and it’s the topic of this, the penultimate post in my “Science in the Setting Sun” series.
When the Sun and or Moon interact with the atmosphere some pretty amazing and awe inspiring things can take place from time to time, from vast networks of rings and halos to color variations, flashes and distortions. Sun pillars, when you see one, are no exception to say the least.
Sun pillars are seen primarily just after the Sun has gone below the horizon or just as it’s setting and can stretch up to thirty degrees into the sky although typically they have a ceiling of five or ten degrees. Oh, before I get too far, it’s worth pointing out that sun pillars, under the right conditions can be seen below the Sun as well or at sunrise but typical western sunset sun pillars are the most viewed.
As the Sun gets lower and lower on the horizon the far traveling sunlight begins to reflect off plate-like hexagonal ice crystals high in the atmosphere’s cirrostratus clouds. The ice crystals are falling horizontally (on their sides) and rocking slight back and forth. The angle of the ice crystals directs the Sun’s light to you in the form of the beautiful and wonder inspiring sun pillar. Keeping with the tradition of setting Sun colors, you may notice that as the Sun sets lower and lower beyond the horizon, the sun pillar will change colors from yellow to orange and finally to red as the light rays are getting further and further away. You can notice this color change on almost any day during sunset as the surrounding clouds will also transition from white light into yellow, orange and finally red (almost pink). The opposite color sequence takes place during sunrise.
Atmospheric Optics data on Sun Pillars: http://www.atoptics.co.uk/halo/pillar.htm
Atmospheric Optics, same data as above but a specific page detailing Solar altitude and Sun Pillars: http://www.atoptics.co.uk/halo/pillalt1.htm
Weather Online data Sun Pillars: http://www.weatheronline.co.uk/reports/wxfacts/Sun-pillar.htm