Saturday, April 16, 2005

The Green Flash

Over Thanksgiving 1986, Lori Lamel and I went scuba diving on the island of San Salvador in the Bahamas. The island is claimed to be the site of the first landing in the New World by Columbus in 1492. After a day of diving, Lori and I were relaxing on the veranda of the Riding Rock Inn, overlooking the sea and the beautiful evening sky. We were joined by another couple, an eye surgeon, and his wife, a nurse. They had been married for seven years, had a practice in the States for part of the year, but every year journeyed to some tropical country where, at their own expense, they set up an clinic and performed eye surgeries on village children. They described all this in a very lovely, serene and modest fashion.
As the sun began to go down, they told us that they had heard of a spectacular optical effect called "The Green Flash", that occurs at sunset. They themselves had never seen it, but they had been watching sunsets for years, hoping to see it together. The wife disappeared into the Inn for some reason, while the three of us remained watching as the sun dipped below the horizon. Then an incredible emerald flash left Lori and I gasping. We were excitedly jabbering away when the wife reemerged onto the veranda. When she realized the three of us had actually seen it and she hadn't, the faces of both the husband and wife fell. Lori and I caught the looks passing between the two of them and our excitement sputtered to a halt. They had so wanted to see it together, they had been watching for years and now their charming fantasy was ruined. Alas.

I've watched for the Green Flash many times since, and while I've seen a couple more pretty good ones, most of the ones I've seen are more like a green tinge.

The Green Flash is the result of two different optical phenomenon. The atmosphere bends short wavelength light more than long wavelengths; and in addition it scatters blue light. So at a certain point as the sun is setting, blue and green light are bent enough to go over the horizon, but red and yellow are not. The blue however is scattered away and we are only left with green.

An Introduction to Green Flashes is a web page devoted to the Green Flash, it's also the source of the photograph at the top of this post. After returning from the San Salvador trip I found the following article, and recall enjoying reading it at the time: "The Green Flash," by D. J. K. O'Connell, in Scientific American, January 1960, pp. 112-122.

This year I've started hearing about another, probably unrelated Green Flash phenomenon. It's been reported that after drinking several bottles of Heineken beer, if an empty bottle is held up to the setting sun, a green flash can sometimes be perceived. These reports tend to originate in Cabo San Lucas, Spring Break and other similar venues.

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