A summer shower brings renewal, a cleansing of the air, the sky, and the land below. It replaces the dog days’ heat with air so brisk it snaps, and that alone makes up for the slight inconvenience of rain. But old mother nature has even more in store - as a finale - a rainbow.
The shimmering vision spreading across the sky is made of sunlight that travels through the mysterious interior of raindrops. Sunbeams pierce the watery shell and ricochet like well-aimed billiard balls, finding their exit at the precise point that allows you to see them in all their splendor.
The droplets of water act like miniature prisms, breaking up the sunlight into its component colors, producing a spectrum that paints the sky with wide ribbons of light. When the sun hangs low in the west, the bow occurs high in the eastern sky. Conversely, when the sun is higher, the arch appears closer to the horizon. And right around midday the sun is too high overhead to produce a rainbow at all.
The shape of the bow is a result of the way your eye perceives the light patterns. Imagine your eye as at the tip of an old-fashioned ice-cream cone, while the rainbow is at the outer edge. If the horizon weren’t in the way, you could actually see a “raincircle” instead of a rainbow. On occasion, someone in an airplane that’s flying away from the sun sees such a kaleidoscopic bull’s-eye, but those of us who remain earthbound have to settle for a simple arch - unless there’s a double rainbow.
The size of the raindrops determines whether you see a single or a double arch in the sky. A large water droplet takes on a flattened shape, but it takes a spherical raindrop to produce the mirror image needed to create a double rainbow. And it is a mirror image - the second rainbow occurs when light rays have bounced one extra time inside the falling raindrop, so that the colors of the upper bow are in reverse order of those in the lower one.
Our biggest double rainbow sighting occurred at Organ Pipe National Monument in Arizona. We pulled into the campground in late afternoon, accompanied by two other motor coaches full of traveling friends. Still discussing our vacation plans over our CB radios as we made camp, we suddenly heard an unfamiliar voice call “Breaker - breaker - there’s a double rainbow in the east!”
Evidently we’d tapped into the local party line, because soon every rig in the campground stood empty. Everyone milled about, sharing the memory of a splendid necklace crowning the Ajo Mouniains far away.
We’ve spent many years chasing rainbows - sometimes in dreams , sometimes in our motor coach as we hurried in the direction of a retreating storm. Yet, no matter how fast we drive, the rainbows always receed at the same pace. The triangle of sun, raindrops, and observer remains constant, so that as you move, a different part of the shower takes over the illusion. But the visual effect is that of a rainbow on the move.
We were able to “relocate” a rainbow to suit our own purposes one year at Sunset Crater when photographing one of the most impressive rainbows we’ve seen. Sunset Crater is a cinder cone that takes its name from the ruddy tint it steals from the setting sun. On this particular evening the nearby campground had been drenched by a summer shower. The clouds scudded eastward, leaving a rainbow in their wake, one determined to outdo even Sunset Crater’s evening performance.
In strong daylight sunbeams are white in color, and a raindrop normally converts white into the seven colors of the rainbow. But if the light striking a raindrop is red from a brilliant sunset, the rainbow arcs across the sky in shades of rose. Our attention was divided between the sunset in the west and a vivid red rainbow that almost, but not quite, embraced Sunset Crater in the east. By moving only 50 yards away from our campsite we were able to re-situate our red rainbow over the cinder cone where it seemed to belong. Then we took the picture.
Since most of our really memorable rainbows have appeared in the Southwest, we weren’t surprised to read that eastern New Mexico ranks as one of the two best spots in the continental United States for this phenomenon. It shares the honors with Florida. What do two such widely separated and drastically different locales have in common? During the summer months they have the most dependable afternoon showers - perfect conditions for rainbows.
No matter where they occur, rainbows are always a surprise and a delight, a reminder that dark clouds promise more than a silver lining. They just might be the prelude to nature’s most colorful light show in the out-of-doors.
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