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.
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.
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.
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.
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.
External links
- A Green Flash Page, Andrew T. Young's page with comprehensive explanations and simulations.
- Straight Dope Article on the Green Flash from Cecil Adams
- Green flash photos
- Astronomy Picture of the Day from NASA
- Le rayon vert by Eric Rohmer