Sunday, September 07, 2008

Rainbow over Nanticoke, September 6 2008

Because we could all use more rainbows in our lives.

I was coming down yesterday from a long day of bookcase assembly, unstocking, rearranging, and restocking in the way I usually do: I was screwing around on the computer. It occurred to me that it was around sunset, and I remembered the admonition repeated in Minnaert's Light and Color in the Outdoors that you should never miss a sunrise or sunset if you can help it. I glanced up at the window high above my right shoulder and saw that the sky was glowing golden.

I called out to my mom to take a look, since it is wrong to keep such a thing to yourself, and she called back that there was a huge rainbow in the sky over our neighbor's house. Which I should have expected, what with the outer arms of Tropical Storm Hanna having skimmed across the area earlier in the day.

But it was sunset, or very close to it, so I realized this was going to be a big rainbow.

It was.
At 7:21 PM only the left leg was visible, though it was accompanied by a secondary bow faintly visible to its left. I had actually been reading my copy of the reprint of Carl B. Boyer's 1959 treatise The Rainbow: From Myth to Mathematics earlier in the day, and it explained how each color in the main "first order" rainbow is the result of a single total internal reflection in a raindrop, while each color in the secondary or "second-order" rainbow is the result of two total internal reflections. As for the "third-order" rainbow that results from three total internal reflections - this rainbow actually presents itself as a circle around the Sun! Boyer did not cite any examples of observations of this surprisingly-placed rainbow, at least not in the section I was reading. (Such a rainbow should not be confused with a halo around the sun, which results from light reflecting off of flat ice crystals.) Note that the sky between the primary and secondary rainbows is darker than the sky to the right of the primary bow. Note also the way the rainbow vanishes behind the clouds at its base, indicating that the raindrops that form this rainbow are either behind or entirely above those clouds.

Two minutes later, you can clearly see that this leg is nearly vertical at its base. This rainbow is about as big as it can get. If you could view it across the entire sky it would appear to be a semicircle.

In fact, you could view a lot more of it than I originally noticed. At 7:24 I backed the zoom off and got this image. The rainbow can be followed to the cloud above and to the right of the eagle weather vane on my neighbor's house, about 1/3 of the way from the top of this photo.

I watched clouds blowing in from the East,obscuring the rainbow as they came. Then my attention was distracted as two of the neighborhood feral cats came out to frolic - Spookybear, the black cat who from his earliest days has had no fear of humans, and Dot, his nearly-identical littermate, distinguishable only by the tiny patch of white on her head.*

When I looked again to the sky, the rainbow was gone.

But the skyshow was not over.

Again we were treated to a golden sunset - unsurprising, since the golden glow in the sky was what had caught my attention scarcely a quarter-hour before. I photographed it to save it for future viewing, and to share it with everyone else.

Tonight's sunset didn't manage to catch my attention. To be honest, I forgot to look when it happened, two hours ago. But I have yesterday's. Maybe I'll get to see tomorrow's.

*Sexes have been assigned to these cats somewhat randomly. Mommy, the Tabby mother of the brood, is obviously a female. Butterfly, the black-and white father who sported a butterfly-like pattern on his face, is now missing and presumed deceased. Spookybear is thought to be a boy and Dot a girl. Squiggles, the Tabby with a squiggly pattern to her stripes, is thought to be a girl. No other siblings are still in the pride, though Socks, a multicolored subadult with white feet who showed up a few weeks ago, is believed to be a second-generation member of the family.

No comments: