The "Green Flash"…

The above inferior-mirage flash image sequence is hosted by Wikipedia , captured by photographer Mila Zinkova at Santa Cruz, CA. The large, top image is the final last glimpse. See Andy Young’s detailed explanation on the Wikipedia image page.

UPDATE: Paul Kamen’s inferior mirage green flash video is excellent — very short, a lovely view of a yacht sailing in front of the Golden Gate Bridge. This video is authentic – most of the others we found were fakes.

We are still trying to see a green flash and of course to capture a decent photograph. Since we have internet access here at Ilot Maitre in New Caledonia we’ve done a bit of elementary re-searching on the subject. It turns out that:

** there are several types of atmospheric phenomena that produce different “green flash” effects;

** the green flash effect can occur at sunrise as well as sunset, and over low-flat land as well as over the ocean.

A very clear explanation can be found at Paul Doherty’s excellent Scientific Explorations and Adventures. Paul’s illustration at left shows the basic differential refraction which very slightly separates the long from the short wavelengths. Paul wrote:

The highest blue image of the sun and lowest red image combine with the central green image to create a white sun with a blue top rim and a red bottom rim.

(…) The same temperature gradients that produce mirages can strongly influence the shape of the sun at sunset and the shape and duration of green flashes.

A sunset through an atmospheric temperature gradient which would produce an inferior mirage causes the bottom of the sun to stretch down toward the horizon and broaden out. This occurs when cold air is over a warm ocean. These flashes are common over tropical oceans. They also happen over temperate oceans when cold air masses move south over warmer water. Most common green flashes are produced by inferior mirage enhancement. The average length of these green flashes in the tropics is 2 seconds.

A word on Paul Doherty: he is an MIT-trained physicist (Ph.D. in solid-state physics). Perhaps more important to us lay folk, Paul has been since 1986 a prime-mover at San Francisco’s famous Exploratorium.

In 1986, I came to the Exploratorium Teacher Institute and began my exhibit-based explorations in science. I became the co-director of the Teacher Institute in 1990 and the founding director of the Center for Teaching and Learning in 1992. Since 1997 I have been a senior staff scientist at the Exploratorium. I am also a visiting scientist at Tom Tits Experiment in Sweden and an adjunct professor of physics at San Francisco State University. In 1999 I received the “Administrator of the Year” award from the California Science Education Advisory Council for my work directing teaching programs at the Exploratorium. In 2002 I was awarded the Distinguished Teacher Award by the American Association of Physics teachers, Northern California Section. In 2003 I was given the NSTA’s Faraday Award for excellence as a science communicator.

So, not only is Paul a physicist, he is a very cool guy (including all sorts of adventuring).

Astronomer Andy Young of San Diego State University is an authority on the green flash. I think you can find everything else you might want to know at Andrew’s Green Flash homepage.

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