A rainbow at Petit Manan Island, Maine Coastal Islands National Wildlife Refuge in Steuben. Photo courtesy of Kayla Pelletier/US Fish and Wildlife Service/Creative Commons.
There has to be a rainbow around here somewhere.
I was thinking this while I was driving along state Route 9 late one summer afternoon, on my way home.
The sun behind me was throwing clean, gorgeous light over everything. The sky ahead of me was dark with blue-black summer clouds, and raindrops were hitting the windshield.
Low-angled sunlight beaming through rain means there’s an arc of blue, yellow and red light somewhere, if my eye could only pick it up. Meaning, if I were positioned at the right angle to catch reflections from the drops.
It’s hard to know exactly why, but rainbows have made hearts leap at least since Noah’s time, if scripture and poetry are any evidence of that unseen feeling. A peculiar sense, which has never faded from human perception, that some kind of grace is being imposed on the world. Or so it seems.
Scientifically speaking, of course, there is no earthly reason to believe a rainbow is anything but a product of mindless physics. Light rays from a setting or rising sun strike raindrops and then are refracted inside the drops, which are not tear-shaped, but spherical. When the light hits the back wall of the drop, its path is deflected, and it reflects toward the sun. A person with his or her back to the sun catches that refracted light in his or her eye.
The colors arise from the light reflecting out of each drop at different angles. White light is made up of all the colors; the drop refracts out the spectrum. The angle of the light’s reflection determines the color your eye picks up — blue, yellow, red and everything in between — depending on where you’re standing.
No two people see the same rainbow. It has no location in space. The rays refracted in and reflected out of the drops form a cone of light, with the tip at each person’s eye. If you’re high up, you can see almost a whole rainbow circle or, really, disk. Each person sees his or her own cone, although the colors sort out the same way for everyone. In the bright primary bow, blue is the innermost band and red the outermost because of the angle of reflection for each wavelength of light.
The “rainbow angle” for deep red light at the rainbow’s edge is 137.5 degrees, a number that also turns up in ratios found in the shapes of spiral galaxies and flowers, among other natural objects. To me, this feels like a lot more than mere coincidence, but what do I know? Beauty is in the eye of the beholder.
When the sunlight is refracted twice inside each drop, a fainter secondary bow develops. Its colors mirror the primary: red on the inside, blue outside. Beyond the secondary bow, sometimes third and fourth bows appear when the light reflects three or four times inside the drops. There’s a darkness between the primary and secondary bows because the drops along the angles of sight between the two don’t send light into your eye. That darkness is called “Alexander’s Dark Band” because it was observed in ancient Greece by Alexander of Aphrodisias.
While I was driving, the rainbow was revealed to me. It arced up over the trees of Ward Hill in Troy, gorgeous and hopeful in the distance, whatever distance it was. I recollected an enormous, vivid rainbow at which I stared over Warden’s Hill in Northumberland, England, one summer evening 20 years before. Attached to that cone of light pouring into my eye was the woman back across the ocean in Waldo County who eventually would become my wife, and if you think that rainbow was merely a mindless hallucination of sun and rain, you’re wrong. My English friends were astonished by it, too, and had their own reasons why.
That afternoon on Route 9, the two rainbows were bound each to each. One when life began, the other, thankfully, now I’m growing old. A joy forever, or so it seems.
Dana Wilde lives in Troy. You can contact him at naturalist1@dwildepress.net. His book “Summer to Fall: Notes and Numina from the Maine Woods” is available from North Country Press. Backyard Naturalist appears the second and fourth Thursdays each month.
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