Addiction Sails the SF Bay

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Green Flash

06 March 2006 | San Francisco


I went for a beautiful sunset sail the other day. The wind was 18-20 when I got out about 3pm. Sierra (my Golden) and I set out for Angel Island. The conditions were perfect for the flash. At 5:30 we were near Alcatraz and the sun was perfectly framed by the Golden Gate Bridge. As the sun lowered in the sky it hit the horizen and in the final seconds a huge green flash was emitted. It was breathtaking!. I let out a huge cheer and great feeling of joy filled my body. Sunsets are cool but green flashes are awesome.

Some folks don't believe they happen, but folks I am here to tell you they are real. That was the third one I have seen. I have even read that it can happen at sunrise. Here is the explanation:

What is the Green Flash?

Like the name says, it is a flash of green seen at the beginning of sunrise and at the end of sunset, just above the disk of the setting sun. It usually appears in a clear sky. The flash can also be blue, yellow, green or violet. Green, however, is the most common.

What Causes the Green Flash Effect?

The green flash has much in common with the ordinary, everyday red and orange sunsets. The same characteristics and conditions are shared by both. The setting sun doesn't just happen-behind the glowing colours, science is at work.

What the human eye sees during a sunset are bent light rays from a sun already down behind the horizon. The atmosphere is responsible for this bending. Therefore, what appears to be the tip of the sun sliding out of view is, in reality, an image created by these bent light rays.

A quirk of the atmosphere is that it scatters blue light more than any other colour of light. So, even though the blue light is "bent" the most, its scattering causes its colour to be diffused and spread across the sky. In this way, the warm glows of red and yellow remain to colour our sunsets, while the sky is blue.

During the average sunset, first the red vision of the sun vanishes and then the yellow, green, blue and violet. Blue and violet flashes are less common than green flashes because a haze in the air removes the violet and the blue, too, leaving the green flash as the last spurt of light visible on the "top" of the sun. If the air is very clear, a "violet flash" occurs.

Guidelines in Seeking the Green Flash

The following are guidelines to optimize the novice's chances of viewing a green flash. These are general guidelines only and, as always with natural phenomenon, no hard and fast rules apply.

For eye protection reasons, it is not safe to stare right into the bright sun (eyes can be injured), so try to only look at the sunset when it is directly on the horizon. If you're hoping to catch the green flash, have someone else let you know when the sun reaches this level.

Location:

Flat horizons are best, so the Lake Huron Shoreline lends itself to ideal viewing conditions. Pick a bench, bring a lawnchair or blanket or view the sunset from the comfort of your car. Tall buildings, mountaintops, airplanes and air balloons also make great vantage points but are in limited supply here!

Good Visibility:

Reasonably clear air is more conducive to green flash sightings than smoggy or murky air often hanging over a city. Again, the Lake Huron Shoreline is blessed with clean air and a clear horizon.

Make the Image Bigger:

The majority of green flashes is teeny and, to the beginner, would pass unnoticed. Using binoculars or a camera viewfinder with a long telephoto lens is advisable. But remember, if it hurts your eyes to look at the bright sun, don't! Wait until the sun drops lower onto the horizon.

Conditions:

Green flashes usually occur when the water temperature is warmer than the air, so during the summer months is not necessarily the best viewing time on Lake Huron. Flashes are dependent on the weather, latitude and season. Good conditions are often created the day after a cold front passes through.

Stay Awhile:

Hang around and watch the horizon for a bit after the sun sets. You may be rewarded by seeing the sun reappear and give a green flash or you may witness a "Green Ray" display.
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