Saturday, June 12, 2010

Strange Tales: The Antisun Pillar

Wednesday, June 9, 2010. Sunrise. Partly cloudy.

The rising sun cast sunbeams into the sky. Crepuscular rays, if you want to be technical. More technically: the light from the sun was being reflected off of dust and suspended water droplets and spiderwebs and whatnot in the air, becoming apparent only where clouds blocked the illumination, casting shadows in the sky.

I was heading West, and home. It had been a twelve-hour night, my first back after four days off, and I was glad to be done with it. I could not see the sun rising behind me, but I could see the sunbeams skipping across the sky before me, broken up by the clouds. In some places the beams converged on the antisolar point on the far horizon. It was quite a sight.

I wished I could photograph it. But taking photos while driving a car moving at highway speeds is a dangerous proposition. You had damn well better make sure the picture is worth the risk.

A little past the midway point between work and home, I decided that what I was seeing was worth the risk. I fumbled with my camera phone, held it up to the windshield, and hoped for the best.

For the life of me I don't know what I was seeing. It's hard to see in the picture above, but on the left between the nearer light pole and the distant sign there is a beam of light coming straight out of the Western horizon. It didn't look right; it was thick and non-converging, not like what I would be expecting at the point where crepuscular rays meet at the antisolar point. It looked like a distant region of non-rain bordered by two regions of rain falling straight down through still air. But the clouds didn't look like they were dumping rain.

It stayed ahead of me as I continued West. This picture was taken about a minute after the first, about a mile down the highway, and the pillar is now more obvious, dead center. It looked almost like a sun pillar (as seen here, for example), but white, and broader, and opposite the sun.

So what was it? Minnaert states in Light and Color in the Outdoors that crepuscular rays are actually easier to see near the antisolar point, though in my experience this is not the case - perhaps the nature of the atmosphere has subtly changed since he wrote this, with greater amounts of pollution or even dispersed condensation from the contrails of jet airplanes (which were rare when he wrote the original version of the book in 1954) blocking the undisturbed passage of these rays across the dome of the sky. War this a lone unblocked ray that had passed almost directly overhead and therefore appeared to be coming straight down into the horizon? Was it some antisolar analogue to a sun pillar? Was it just a dry patch between two distant downpours? Or was it something else?

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