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.


Green flashes can be observed from any altitude (even from the air). They are usually seen at an unobstructed horizon, such as over the ocean, but are possible over cloud-tops and mountain-top as well.

Contents

Explanation

Types of green flashes

Blue flashes

In the media

Writing

Film

Music

TV

Food

References

External links

Explanation

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.

Types of green flashes

The green flash is actually a group of phenomena, some of which are listed below:^[1]

Type	Characteristics	Conditions	Best seen from...
Inferior-mirage flash	Joule's "last glimpse"; oval, flattened below. Lasts 1 or 2 seconds	Surface warmer than the overlying air	Close to sea level
Mock-mirage flash	Indentations seem to "pinch off" a thin, pointy strip from the upper limb of the Sun. Lasts 1 or 2 seconds	Atmospheric inversion layer below eye level; surface colder than air	The higher the eye, the more likely; flash is most obvious when the eye is just above the inversion
Sub-duct flash	Large upper part of an hourglass-shaped Sun turns green for up to 15 seconds	Observer below a strong atmospheric inversion	In a narrow height interval just below a duct (can occur at any height)
Green ray	Green beam of light either shooting up or seen immediately after sundown. Usually few degrees long, lasting several seconds	Hazy air and a bright green flash acting as a light source	Unknown

The majority of flashes observed are inferior-mirage or mock-mirage ones, with the others constituting only 1% of reports. Some types not listed in the table above, such as the cloud-top flash (seen as the sun sinks into a coastal fog, or at distant cumulus clouds), are not understood.¹

Blue flashes

Very occasionally, the amount of blue light is sufficient to be visible as a "blue flash".^[2] The term should not be confused with the similar usage of 'blue flash' referring to the blue light seen in nuclear criticality accidents.

In the media

Writing

★ Jules Verne, the early French science-fiction writer, wrote a book named ''Le Rayon vert'' (''The Green Ray'', 1882) whose heroine, Helena Campbell, is chasing this elusive phenomenon. According to legend, those who see the ray will not choose wrong love.

★ Victoria Holt, the gothic fiction writer, makes the green flash a major part of her novel, ''The Pride of the Peacock.''

★ Carl Hiassen, an American writer, wrote a novel called ''Flush'', in which he mentions the green flash several times and the characters see a green flash at the end of the book.

★ Raymond Feist, a fantasy writer, cites the green flash as one of the rare treasures of a life of traveling.

★ The green flash features several times in the works of Arthur C. Clarke, British science-fiction writer.

★ The green flash is mentioned in the novel ''Middlesex'', by Jeffrey Eugenides.

★ There is a fragment in Spanish by Julio Cortazar on the "Green Ray".[1]

★ Roger Penrose in his book ''The Road to Reality'' includes a green flash in the epilogue.

★ Girl of the Sea of Cortez written by Peter Benchley includes writing about a green flash.

★ Alec Waugh's novel ''Island In the Sun'' contains references to the green flash.

Film

★ Éric Rohmer, a French film director, made a movie named ''The Green Ray''. The ray is visible in the last scene.

★ The green flash is used in '' to indicate that a soul has returned to the world of the living. The characters also have to look for it, as it is the only way to exit Davy Jones' Locker.

Music

★ Sonic Youth's song "Jams Run Free" describes the occurrence in its chorus.[2]

★ Sr. Chinarro's album "El Fuego Amigo" contains a song called "El Rayo Verde" ("The Green Ray").

TV

★ In the children’s TV series, ''Arthur'', in an episode about New Year's Eve and Arthur's inability to stay up through it, Prunella says that a green flash appears across the sky at midnight on New Year's Day, but if it doesn't appear, it stays the same year for another year.

Food

★ The Green Flash Restaurant in Captiva Island, FL

★ The Green Flash Restaurant in Pacific Beach, San Diego, California.

★ The Green Flash Brewing Company in Vista, California.

References

1. Young, A. "Green flashes at a glance" (2006), San Diego State University page. Retrieved on 09/05/07.
2. "The Green Flash, BBC Weather online. Retrieved on 09/05/07.

External links

★ A Green Flash Page, Andrew T. Young's page with comprehensive explanations and simulations.

★ Green Flash - Atmospheric Optics, explanations and image gallery, Les Cowley's Atmospheric Optics site.

★ Green flash photos

★ A Green Flash from Astronomy Picture of the Day, NASA

★ Short sequence of a green flash