University Lowbrow Astronomers

Atmospheric Optical Phenomena.

by Mark S Deprest
Printed in Reflections: February, 2009.

In my many years (54 of them) on this spinning ball of cosmic flotsam, I have seen many wonderful and amazing things. Some of these have been man-made, but those that were naturally created seem to hold a special place in my memory. The geological spectacles of the National Parks like Grand Canyon, Arches, Bryce, Yellowstone and Sequoia to name a few are sights that everyone should see and although these are dynamic and changing, its on a geological time scale. Lightning, Aurora, Rainbows, Sun & Moon Halos, Sun-dogs, and Sun Pillars are also dynamic and changing but are brief and fleeting on a time scale of minutes or seconds, so in order to see any of these things one needs to be in the right place at the right time and looking in the right direction.

Recently I was in the right place, at the right time, and was looking in the right direction. The results fortunately were caught on my cell phone’s camera as Sun Pillars.

Sun Pillar #1

Sun Pillar #1

Sun Pillars are caused by “plate-like” crystals in the atmosphere. Normally these plate-like crystals only form in the high clouds, but sometimes when the temperature is very cold near the ground these platelike crystals can form much lower in the atmosphere and then very strange and wonderful things can happen.

On the morning of January 12th 2009 that happened and on my way into work, around 05:30, I witnessed something that just blew me away! Unfortunately I was driving at the time and wasn’t able to get a picture of exactly what I was seeing. However, as luck would have it, the Astronomy Picture of the Day website featured a picture that same day of the phenomena I saw!

Now, there seemed to be some question as to why these “Light Pillars” fan out at the top and the answer (although slightly debated) is that toward the top of these pillars a different shaped crystal is more prevalent; this type is called a “horizontal column” crystal.

Whenever I see atmospheric optical phenomena I like to find out how they were created and the website that usually does the best job is: www.atoptics.co.uk . Knowing how and why they happen gives me a greater appreciation of “being in the right place, at the right time and looking in the right direction.”

Unlike the crystals producing sun pillars, those making tall artificial light pillars need not be strongly tilted. The column producing pillars are approximately midway between the eye and the light source. The higher the crystals in the atmsphere, the taller is the pillar. When the crystals are very high—or the light sources are close—the pillars seem to radiate from overhead, the zenith.

Each dot represents the tip of a line perpendicular to a side face of the crystal as it rotates about two axes. The dots concentrate at the zenith. Side faces spend more time nearly horizontal and so produce pillars.


Column crystals probably produced this pillar imaged at Oslo, Norway by Erik Brenna (site). The pillar is unusually tall, some 20°, and is topped by an intense upper tangent arc also generated by singly oriented columns. ©Erik Brenna, shown with permission.

How can horizontal column crystals make pillars? Pillars are created by reflections from approximately horizontal crystal faces but the side faces of columns are inclined at all angles.

Getting back to the “light-cicles” (my name for them) that I saw on my way into work at 05:30 on that frigid morning, I wasn’t able to see the source of my light-cicles due to intervening trees and houses, so they appeared to me to look a lot like curtains of aurora. One problem, they were only in my southern sky! Also, as I drove east on Geddes road, parallel to my light-cicles their aspect to one another changed, which indicated that they were hanging in mid-air at differing distances from me. My light-cicles were different colors and only the brightest ones tending to fan out at the top. I was totally mystified by what I saw and as I turned my car south onto Canton Center road, I discovered the source of my light-cicles; the poorly shielded parking lot lights of the Home Depot / Kroger’s at the corner of Michigan avenue and Canton Center road. The different colors were a result of the different types of lights; low pressure sodium lights were yellow-orange, halogen lights were white and the mercury vapor lights were blue-white. Although these light-cicles were the result of something manmade, they did have to be combined with just the right natural conditions and that makes them wonderful and amazing!

The following images will help you understand the dynamics of what I saw. For more info please check out the Atmospheric Optics website at: www.atoptics.co.uk .

 

Photo Credits

The first two pictures were taken by Mark Deprest. The last four pictures appear with the permission of the photographer Aigars Truhins. The graphics are used with permission from the website www.atoptics.co.uk

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Copyright © 2013, the University Lowbrow Astronomers. (The University Lowbrow Astronomers are an amateur astronomy club based in Ann Arbor, Michigan).
This page originally appeared in Reflections of the University Lowbrow Astronomers (the club newsletter).
This page revised Sunday, March 9, 2014 4:30 PM.
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