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My B-I-L mentioned the Green Flash Phenomena after I returned from vacation. I had never heard of this and so, was not looking for it while enjoying the beautiful sunsets in the Turks and Caicos. Then I was looking through my vacation photos and look what I found!
More on the Green Flash from Wikipedia:
Green flashes are rare optical phenomena that occur shortly after sunset or before sunrise, when a green spot is visible for a short period of time above the sun, or a green ray shoots up from the sunset point. Green flashes can be observed from any altitude (even from an airplane). They are usually seen at an unobstructed horizon, such as over the ocean, but are possible over cloud-tops and mountain-tops as well.
The reason for a green flash lies in refraction of light (as in a prism) in the atmosphere: light moves more slowly in the lower, denser air than in the thinner air above, so sunlight rays follow paths that curve slightly, in the same direction as the curvature of the Earth. Higher frequency light (green/blue) curves more than lower frequency light (red/orange), so green/blue rays from the upper limb of the setting sun remain visible after the red rays are obstructed by the curvature of the earth.
Green flashes are enhanced by atmospheric inversions, which increase the density gradient in the atmosphere, and therefore increase refraction. A green flash is more likely to be seen in clear air, when more of the light from the setting sun reaches the observer without being scattered. We might expect to see a blue flash, but the blue is preferentially scattered out of our line of sight and remaining light ends up looking green.
With slight magnification a green rim on the top limb of the solar disk can be seen on most clear-day sunsets. However the flash or ray effects require a stronger layering of the atmosphere and a mirage which serves to magnify the green for a fraction of a second to a couple of seconds.