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Catching the Green Flash

© Jill Florio

Getting the Green Light

The green flash - a little-known, seldom-seen, mysterious sunset phenomenon. Some argue it doesn't exist, but to me, that's just sour grapes. I've seen it eleven times, so far, and seven of those appearances were over the ocean, in San Diego.

It's worth looking, wherever you may be.

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The Truth is Out There

I dig celestial phenomena. The Hale-Bopp comet was fun to follow as it swooped across the night sky in the 90s. I love a good lunar eclipse, and solar eclipses are even more exciting. I've seen the aurora borealis and zodiacal lights, both many times.

I have yet to catch a lunar occultation (when the moon passes across the apparent path of a planet or star and blocks it from view) or even a planetary one(when a planet passes in front of a star). But I always enjoy when planets exhibit interesting lineups and conjunctions in the night sky.

The green flash is simply thrilling to see. When it occurs, it's usually so fast that you aren't even sure what you saw. People have reported seeing a blue flash from time to time, and there are pictures documenting this rarer occurance.

Photographs here document different appearances to help you get a handle on what you're looking for.

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You've Been Flashed

When the sun passes through the dividing line between earth and sky, different waves of light are extinguished in sequence. Light waves on the red end of the spectrum sink from view first. Blue and purple waves are pretty much scattered across the sky (that's what makes the sky blue). Green waves are what's left. When conditions are clear and the horizon is at the correct angle, you will see a momentary spot or ray of green. It's very quick.

In the case of the setting Sun, the upper limb is green (or sometimes blue). If the horizon is provided by the sea or by very distant flat land, and the air is very clear for a hundred kilometres or more towards the sunset, then it is possible to see the green flash. As the upper rim of the setting disk approaches the horizon, it begins to spread into a thin bar of light, then runs through the spectrum from orange to yellow, then pale green, and finally reaches a deep emerald colour for two or three seconds. Under favourable conditions a brief blue blob of light may be seen after this, but exceptional clarity of the air is needed.