Half of the visual field consists of everything from eye level downward: the contents of the world. This realm is temporarily losing its luster, since colorful leaves have fallen and brightly hued birds have largely headed south. But the other half — everything above the skyline — is actually getting better.
There are more clouds during our cold season, which provides more visual variety than an unbroken blue firmament. And the frigid air offers phenomena that display the Sun’s colors, yielding a celestial bounty. Start by noticing the white fringes on clouds near the Sun. Sooner or later a strange, diffuse, modern-art design will materialize there, and you’ll realize these are not spectral colors. Strangely enough, cloud-fringe hues are never those that make up rainbows. No green, blue, red or orange. Instead, the patterns consist of everything else — purples, browns, pinks, aquamarine, all the hues never found in rainbows or on wall spectra cast by prisms.
When you see it, you can tell a companion: “Wow, look at that cloud iridescence!” And you’ll be right, because it’s a phenomenon caused by diffraction (the interference among light waves) not by refraction (the bending of light waves.)
But refraction is cool, too. Its most common effect is when sunlight hits hexagonal ice crystals in very thin, barely-there clouds. Then you often see sun dogs. These bright spots that can be white or colorful sit 22 degrees to the right or left of the lowish Sun. Officially called parhelia, sun dogs appear a few times a month over our region.
Only slightly less common are the wonderful rings around the Sun or Moon. This is the 22-degree halo, whose size never varies. Hold a spread-open hand at arms’ length, and if you place your thumb tip against the Sun or Moon, your pinky tip will just perfectly mark the halo’s position. The halo’s innermost edge is sometimes reddish.
These are the commonest atmospheric wonders. But keep looking and eventually you’ll capture the weird rare ones. The upper tangent arc is a white U-shaped “bowl” that seems to balance at the very top of the halo. It’s the only refraction phenom whose appearance changes with Sun-elevation. When the Sun is high, the bowl is more spread out.
Finally, favorite rare designs include the 46-degree halo, which takes up an enormous piece of the sky. And the parhelic circle. This is a curious white line that goes horizontally sideways from the Sun to pass through the sun dogs and continue completely around the sky. It always stays the same height as the Sun in all directions, parallel to the horizon and is nothing short of bizarre.
Painterly marvels to keep your eyes busy and your spirit elevated.
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