A fleeting image of a ‘green flash’ – an optical phenomenon lasting no more than two seconds – was captured in this photo by Judy Flagg of Irvine.
She shot it Aug. 22 in Laguna Beach, and an expert on green flashes, adjunct professor of astronomy Andrew T. Young at San Diego State University, said he had “no doubt” after examining the picture that it is a genuine green flash.
Wesley Traub, a senior research scientist at the Jet Propulsion Laboratory in Pasadena, also said the image looked like a genuine green flash, with the “right color and length of time and position at or above the apparent disk.”
Young, who has put together a Web page with images and a wealth of information about green flashes and has photographed many himself, helped us out with the explanation.
There are a variety of types of green flash, he said; in Southern California, a common type happens when warm air sits on top of cold air, and when we view the sunset while standing in the warm air and looking down into the cold air.
“The sharp contrast in density where the warm air overlies the cold air acts like a lens, forming multiple and inverted images,” Young wrote in an e-mail.
Refraction in the atmosphere at the horizon, meanwhile, raises the sun’s image; a rim of green light normally too narrow to be seen with the naked eye can have more refraction under these conditions, so it can appear above the sun.
Where the “multiple and inverted images” touch, Young said, “the atmospheric lens magnifies enough to make the green upper rim of the sun visible to the naked eye.”
He said this type of green flash is called a “mock mirage.” Seeing two dots instead of one streak of green happens because of waves in the atmospheric inversion, he said, but he, too, has photographed green flashes with two dots before.
Flagg, who is retired, said she was shooting a sequence of sunset images when she happened to snap the picture at just the right moment.
“I don’t think it lasted more than a couple of seconds,” she said. “It’s nothing I’ve ever captured before.”
