It was one of those crackling-cold, minus-twenty nights we get here in Minnesota. The air was so dense that the airplane 20,000 feet above me sounded like it was on approach for landing. As I walked across the street to warm up the car, the snow squeaked like dry Styrofoam® underfoot.
Something odd caught my eye, and I looked up. Just through the bare branches of trees, the street light from the next block cast a distinct, golden beam of light 50 or 60 feet straight up into the sky. That's odd, I thought, the light must be broken…but how could it shine straight up like that? And since when do street lights cast such a distinct beam?
It was clear we were witnessing a wondrous, once-in-a-lifetime phenomenon.
|PHOTO: Tristan Greszko - www.tristangreszko.com|
By the time I picked up my wife in front of the house, we noticed pillars of light balancing atop other lights in the neighborhood too. On our way home, as we passed lighted signs and other cars, it was clear we were witnessing a wondrous, once-in-a-lifetime phenomenon. (Most spectacular was a two-block-long colonnade of light fronting a well-lit used car lot.)
We later learned that what we'd seen were "light pillars." They're caused by a light source—typically the sun or moon, but occasionally artificial sources too—reflecting off of the horizontal surfaces of tiny ice crystals that fill the atmosphere in extreme cold weather.
This experience got me thinking about all the other amazing tricks light plays on us. Here are just a few of the other ones I've experienced or come across through a little research. Maybe you've witnessed some of them for yourself.
The result is...a nearly biblical effect...a multi-hued halo of light seeming to emanate from their head.
CRESCENT SUN DAPPLING – You know about the pinhole projection method of safely following the progress of a solar eclipse: you make a small hole in a piece of cardboard, hold it out and watch the tiny image of the partial sun projected on the sidewalk below.
But have you noticed that the same effect occurs naturally? Most days, the dappled sunlight that seeps through tree foliage actually comprises many overlapping, round pools of light. During an eclipse, though, each of those circles turns into a crescent as the moon takes a bigger and bigger bite out of the sun.
|Elliptical sun dappling during solar eclipse|
GLORIES – You've probably seen a halo around the sun or the moon. But have you seen a glory? Again, it's a type of projection; in this case the "screen" is a mass of water droplets—like a cloud or the spray of a waterfall.
If the observer happens to be standing directly between the sun and those water particles, the result is a Brocken spectre, a nearly biblical effect of the person's shadow, with a multi-hued halo of light seeming to emanate from their head.
|Glory, with Brocken Spectre|
THE GREEN FLASH – Of all the beach sunsets I've experienced, I've never once witnessed the mythical green flash that's rumored to occur at the instant the sun disappears into the sea horizon. I thought it was one of those things where your odds of seeing it improved with the number of tequilas you'd consumed.
Turns out the green flash is a real phenomenon. Apparently the optical mechanism is similar to that of a prism. Since shorter wavelength light (the greens and blues) bends more than longer wavelength light (reds and oranges), the blue-green rays of the top edge of the setting sun stay visible slightly longer than the red-orange ones. I'll keep looking…and counting on the tequila to help.
|The Green Flash|
HEILIGENSCHEIN – Similar to the Brocken spectre, this "holy glow" occurs when a strong sun shadow is cast onto a surface coated in dew droplets. Each droplet acts as a lens to intensify the brightness and project it onto the surface it rests on.
Some of that light also bounces around in each droplet and is cast back toward the sun. (A commercial application of this effect is found in reflective materials like ScotchBright®, where a layer of tiny glass beads replaces the dewdrops.)
CLOUD IRIDESCENCE – This rare refraction phenomenon occurs when sunlight passes through thin, wispy clouds. That keeps most of the light rays from passing through more than a single water droplet, which refracts the light like a prism. (When the rays encounter thicker clouds, they encounter multiple droplets, and the prism effect gets scattered and diffuse.
Because this effect occurs mostly in an area of the sky near the sun, the sun's glare usually consumes it, so it helps if a building, tree or other object blocks one's direct view of the sun.
SHARE THE LIGHT!
These are just a few of the wonders Nature can paint with light. Others I've enjoyed include sun dogs, northern lights, phosphorescence, alpenglow, mirages and many more. Have you witnessed any of these...or others? I'd love to hear comments!
Information in this post not derived from personal experience comes from Wikipedia, as do all photos except Tristan Greszko's wonderful shot of the light pillars.