Green Flash

The Green Flash is an optical phenomenon.

It can be difficult to capture a photo of a “green flash,” an optical phenomenon that can be seen near the upper rim of the sun during sunset or sunrise, when a green flash of light is visible for a moment.

Most of the time, it’s rare to have just the right atmospheric conditions to get a photo of the green flash. The seemingly ever-present northwesterly winds often produce haze near the ocean’s surface that blocks out the faint light from it. In normal years, the summer months see plenty of coastal stratus and fog that often shrouds our coastline.

However, on evenings that were clear, Sean, my 15-year-old son, and I have driven to the coast on many occasions with a camera and tripod in tow hoping to get a photograph of the elusive green flash.

Last year we finally got an okay photo of the phenomenon, but to be honest it wasn’t the best. However, Christina Stead got a great photo of the flash a few years ago. She took the image from about a 100-foot-high vista point near Cayucos. During that sunset the winds were calm, and this condition often produces the best chance of seeing the green flash.

A long time ago, I was incorrectly told that the green flash was the sun shining through the ocean waves. Green flashes are really byproducts of mirages appearing slightly above the horizon and not in the sea.

The cause of this green-colored mirage is mostly due to atmospheric dispersion. The shorter wavelengths of blue and violet light are scattered to a much greater extent than the red and yellow hues by the air we breathe — that’s why the sky is blue.

As the sun sets, the longer wavelengths of the reds and yellows disappear first, leaving behind the greens. In other words, the red image of the sun sets or disappears first, followed by yellow and then finally the green.

I’ve seen green flashes from different altitudes, even from naval aircraft patrolling over the vast expanses of the ocean. One evening during sunset while driving westward toward the ocean, I saw the green flash for nearly 10 seconds. The road gently ascended. The gain in altitude as I traveled westward slowed the apparent sunset from my perspective, allowing me to see a much longer flash.

The green flash can last much longer above the Arctic Circle or below the Antarctic Circle. Here, the sun transitions from the perpetual darkness of winter to the everlasting light of summer. During the equinox, the sun moves along the horizon for an extended period of time. Adm. Byrd reported seeing the green flash off and on for over half an hour during his expedition to the South Pole during the September equinox.

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John Lindsey is Pacific Gas and Electric Co.’s Diablo Canyon Power Plant marine meteorologist and a media relations representative. Email him at pgeweather@pge.com or follow him on Twitter @PGE_John.

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