Key West's Famous Green Flash Sunset

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29 Mar 2017

Sunsets in Key West are an event. Every night, crowds gather in Mallory Square to enjoy the sunset, watch street performers, buy local crafts, enjoy food carts and of course, a cold libation. As the sun sets over the Gulf of Mexico, a few sunset watchers will hold their breath in anticipation of seeing a rare and beautiful sight as the sun vanishes over the horizon … the famous “green flash”.

The Green Flash is a bright green light that flashes across the ocean just as the sun dips below the horizon. The green flash is legendary, and some say it is a myth, like a unicorn or a pot of gold at the end of a rainbow. But green flashes are very real.

Like a rainbow, the green flash is an effect of the atmosphere. When the sun sinks low on the horizon, its light passes through a thick layer of atmosphere which scatters blue and green light out of the line of sight, making the sun appear red-orange. But here is where the green flash comes in.

As the sun sinks out of sight, our atmosphere bends (or refracts) the sun’s light from below the horizon. The colors of the spectrum disappear one at a time, starting with those with the longest wavelengths. Since the air bends green, blue, and violet light more than red, the red light sets first, followed by orange, yellow, green, blue, then violet.  It is a primarily a green light that is seen because more green light gets through. Sounds easy right? But there are a few factors that have to come into play:

  • You must have a clear view of the horizon, over a great expanse of atmosphere, like the ocean.
  • It must be cloudless over the sunset horizon
  • You must be looking just at sunset,at the last moment before the sun disappears below the horizon.

History says that seamen were the first to recognize its existence. Pirate folklore tells us that the green flash signals the return of a soul from the world of the dead.  Today, we like to think seeing the green flash is good luck.  It is certainly a beautiful sight to behold, so keep watching those sunsets…maybe you will be lucky enough to see the “Flash”!