Green flash

Green flashes and green rays 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. It is usually observed from a low altitude where there is an unobstructed view of the horizon, such as on the ocean.

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Its explanation lies in refraction of light (as in a prism) in the atmosphere and is enhanced by atmospheric layering. Whilst we would expect to see a blue light, the blue is dispersed (this is why the sky is blue) and only the green light remains visible.

Related Topics:
Refraction - Light - Prism - Atmosphere - Atmospheric layering

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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.

Related Topics:
Magnification - Mirage

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Jules Verne, the early French science-fiction writer, wrote a book named Le rayon vert (The green ray) whose hero is chasing this elusive phenomenon.

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Eric Rohmer, a French film director, made a movie named Le rayon vert where one gets to see a green ray in the last scene.

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