Green flash over the North Sea, Belgium; photo credit: Hans Hillewaert via Wiki Commons

Outdoor Adventuring: How to See the Elusive ‘Green Flash’

Just before sunrise or sunset, there’s sometimes a band of green light just above the sun, often described as a ‘flash.’ But some swear it’s just a myth. Here’s the truth and how you can see for yourself.

As an avid outdoor enthusiast, I’ve always been captivated by sunsets. Every evening of 2021 so far, I’ve watched from a variety of locations, witnessed myriad color displays, and enjoyed the company of friends and the silence of solitude.

Despite my commitment to chasing the sun, the green flash continues to elude me. So I set out to maximize my chances of catching it.

Read on to learn how to witness it yourself.

sunset
Photo credit: Rebecca Parsons

What Is the Green Flash?

According to Briony Horgan — an assistant professor of earth, atmospheric, and planetary science at Purdue University — the green flash is indeed a real phenomenon and can be green, violet, or blue. Horgan says it’s caused by rays of sunlight refracting in the atmosphere, which depends on the light’s wavelength (color).

“At sunset, when the light has the most atmosphere to be bent by, the sun is surrounded by shadows of different colors — with the blue, violet, and green shadows further out,” Horgan said.

“The red, orange, and yellow shadows are absorbed by the atmosphere, and the blue and violet shadows are scattered by the atmosphere. So the strongest shadow left is usually the green one. This effect is only strong enough to see for a few seconds, hence the ‘green flash.’”

 

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The flash typically lasts only 1-3 seconds, being “most visible during the few seconds when the sun sets below or rises above the horizon.” There are actually four different types of green flashes: inferior mirage, mock mirage, subduct flash, and green ray.

Only the first two are visible to the naked eye. The inferior mirage flash is oval and flat and occurs close to sea level, while the mock mirage looks like thin, pointy strips sliced from the sun and occurs higher in the sky.

Ideal Conditions

To maximize your chances of seeing the green flash, watch as many sunrises and sunsets as possible over a flat horizon on clear days. And remember: Although green is the most common color of the “flash,” it could also be violet or blue.

While on your coastal or desert adventures this spring and summer, be sure to pause as the sun goes down. And if you’re lucky, you may join the ranks of the few to have witnessed the rare yet magical occurrence.

float a river in an inner tube
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