The green flash and green ray are

meteorological Meteorology is a branch of the atmospheric sciences (which include atmospheric chemistry and physics) with a major focus on weather forecasting. The study of meteorology dates back millennia, though significant progress in meteorology did not ...

optical phenomena that sometimes occur transiently around the moment of

sunset Sunset, also known as sundown, is the daily disappearance of the Sun below the horizon due to Earth's rotation. As viewed from everywhere on Earth (except the North and South poles), the equinox Sun sets due west at the moment of both the spring ...

or sunrise. When the conditions are right, a distinct green spot is briefly visible above the Sun's upper

limb Limb may refer to: Science and technology *Limb (anatomy), an appendage of a human or animal *Limb, a large or main branch of a tree *Limb, in astronomy, the curved edge of the apparent disk of a celestial body, e.g. lunar limb *Limb, in botany, ...

; the green appearance usually lasts for no more than two seconds. Rarely, the green flash can resemble a green ray shooting up from the sunset or sunrise point. Green flashes occur because the

Earth's atmosphere The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing for ...

can cause the light from the Sun to separate, or

refract In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenomeno ...

, into different colors. Green flashes are a group of similar phenomena that stem from slightly different causes, and therefore, some types of green flashes are more common than others.

Observing

Green flashes may be observed from any altitude. They usually are seen at an unobstructed

horizon The horizon is the apparent line that separates the surface of a celestial body from its sky when viewed from the perspective of an observer on or near the surface of the relevant body. This line divides all viewing directions based on whether i ...

, such as over the ocean, but are possible over cloud tops and mountain tops as well. They may occur at any latitude, although at the equator, the flash rarely lasts longer than a second. The green flash also may be observed in association with the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

and bright planets at the horizon, including

Venus Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...

and

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...

. With an unrestricted view of the horizon, green flashes are regularly seen by airline

pilot An aircraft pilot or aviator is a person who controls the flight of an aircraft by operating its directional flight controls. Some other aircrew members, such as navigators or flight engineers, are also considered aviators, because they a ...

s, particularly when flying westwards as the sunset is slowed. If the atmosphere is layered, the green flash may appear as a series of flashes. While observing at the Vatican Observatory in 1960, D.J.K. O'Connell produced the first color photograph of the green flash at sunset.

Explanation

Green flash occurs because the

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...

causes the light from the Sun to separate, or

, into different frequencies. Green flashes are enhanced by mirages, which increase

refraction In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenomeno ...

. A green flash is more likely to be seen in stable, clear air, when more of the light from the setting sun reaches the observer without being scattered. One might expect to see a blue flash, since blue light is refracted most of all and the blue component of the sun's light is therefore the last to disappear below the horizon, but the blue is preferentially scattered out of the line of sight, and the remaining light ends up appearing green.Explaining Green Flashes
by Andy Young With slight

magnification Magnification is the process of enlarging the apparent size, not physical size, of something. This enlargement is quantified by a calculated number also called "magnification". When this number is less than one, it refers to a reduction in siz ...

, a green rim on the top of the solar disk may be seen on most clear-day sunsets, although the flash or ray effects require a stronger layering of the atmosphere and a mirage, which serves to magnify the green from a fraction of a second to a couple of seconds. In addition to atmospheric refraction and lensing, another primary cause of the Green Flash may be due to a phenomenon recently discovered by researchers at the Washington University in St. Louis Medical School, which found that when two photons of infrared light collide with a human retina cell, causing what researchers there call "a double hit," it creates the perception of bright neon green.
by Jim Dryden The researchers at Washington U. discovered this inadvertently while working with powerful infrared lasers, which should have been invisible to them, yet the researchers consistently kept seeing bright green flashes from the source of the laser. Because the Green Flash occurs exactly where we would expect the bulk of refracted infrared sunlight (just beyond red but not by much), the most likely hypothesis is that the Green Flash is refracted and magnified infrared light that "double-hits" the retina or camera lens, creating the effect of bright green.

Types

The "green flash" description relates to a group of optical phenomena, some of which are listed below: The majority of flashes observed are inferior-mirage or mock-mirage effects, 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 Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Reprint from Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily influ ...

, or at distant

cumulus cloud Cumulus clouds are clouds which have flat bases and are often described as "puffy", "cotton-like" or "fluffy" in appearance. Their name derives from the Latin ''cumulo-'', meaning ''heap'' or ''pile''. Cumulus clouds are low-level clouds, gener ...

s), are not understood.

Blue flashes

On rare occasion, the amount of blue light is sufficient to be visible as a "blue flash".The Green Flash
BBC Weather online. Retrieved 2009-05-07.

Green rim

As an

astronomical object An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists in the observable universe. In astronomy, the terms ''object'' and ''body'' are often us ...

sets or rises in relation to the horizon, the light it emits travels through Earth's

, which works as a

prism Prism usually refers to: * Prism (optics), a transparent optical component with flat surfaces that refract light * Prism (geometry), a kind of polyhedron Prism may also refer to: Science and mathematics * Prism (geology), a type of sedimentary ...

separating the light into different colors. The color of the upper rim of an astronomical object could go from green to blue to violet depending on the decrease in concentration of pollutants as they spread throughout an increasing volume of atmosphere.Dispersive refraction
by webexhibits.org. The lower rim of an astronomical object is always red.
A green rim is very thin and is difficult or impossible to see with the naked eye. In usual conditions, a green rim of an astronomical object gets fainter when an astronomical object is very low above the

because of atmospheric reddening, but sometimes the conditions are right to see a green rim just above the horizon. The following quote describes what was probably the longest observation of a green rim, which at times could have been a green flash. It was seen on and off for 35 minutes by members of the Richard Evelyn Byrd party from the Antarctic Little America exploration base in 1934: For the explorers to have seen a green rim on and off for 35 minutes, there must have been some mirage effect present. A green rim is present at every sunset, but it is too thin to be seen with the naked eye. Often a green rim changes to a green flash and back again during the same sunset. The best time to observe a green rim is about 10 minutes before sunset.Green and red rims
by Andrew T. Young. That is too early to use any

binoculars Binoculars or field glasses are two refracting telescopes mounted side-by-side and aligned to point in the same direction, allowing the viewer to use both eyes (binocular vision) when viewing distant objects. Most binoculars are sized to be held ...

or a

telescope A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally meaning only an optical instrument using lenses, curved mirrors, or a combination of both to observe ...

to look directly at the Sun without potential harm to the eyes. (Of course, a magnified image might be projected onto a sheet of paper for safe viewing.) As the Sun gets closer to the horizon, the green rim becomes fainter due to atmospheric reddening. According to the above, it is probably correct to conclude that although a green rim is present during every sunset, a green flash is rarer because of the required

mirage A mirage is a naturally-occurring optical phenomenon in which light rays bend via refraction to produce a displaced image of distant objects or the sky. The word comes to English via the French ''(se) mirer'', from the Latin ''mirari'', meanin ...

In popular culture

Jules Verne Jules Gabriel Verne (;''Longman Pronunciation Dictionary''. ; 8 February 1828 – 24 March 1905) was a French novelist, poet, and playwright. His collaboration with the publisher Pierre-Jules Hetzel led to the creation of the ''Voyages extraor ...

's 1882 novel ''

The Green Ray ''The Green Ray'' (french: Le Rayon vert) is a novel by the French writer Jules Verne published in 1882 and named after the optical phenomenon of the same name. It is referenced in a 1986 film of the same name by Eric Rohmer. Plot summary Th ...

'' helped to popularize the green flash phenomenon. A 1986 film also called ''The Green Ray'' uses the green flash and Verne's book as a plot device. Additionally, the green flash has inspired or been mentioned in: *Jules Verne's 1905 novel The Lighthouse at the End of the World * Mario Castelnuovo-Tedesco composed a 1916 solo piano work titled ''Il raggio verde'', op. 9, depicting a musical/emotional impression of the phenomenon. *

John D. MacDonald John Dann MacDonald (July 24, 1916December 28, 1986) was an American writer of novels and short stories. He is known for his thrillers. MacDonald was a prolific author of crime and suspense novels, many set in his adopted home of Florida. On ...

's 1962 novel, ''A Flash of Green'' employs the green flash as a keynote for the events of the story. In 1984, it was adapted into a film, ''

A Flash of Green ''A Flash of Green'' is a 1984 American drama film directed by Victor Nuñez. It was first shown at the Toronto Festival of Festivals and New York Film Festival in 1984, then aired on PBS as an episode of ''American Playhouse'' in 1986. It is base ...

'', starring Ed Harris and

Blair Brown Bonnie Blair Brown (born April 23, 1946) is an American theater, film and television actress. She has had a number of high-profile roles, including in the play ''Copenhagen'' on Broadway, the leading actress in the films ''Altered States'' ( ...

. *

Victoria Holt Eleanor Alice Hibbert (née Burford; 1 September 1906 – 18 January 1993) was an English writer of historical romances. She was a prolific writer who published several books a year in different literary genres, each genre under a different pen ...

's 1976 novel ''Pride of the Peacock'', which uses both the green flash and an

opal Opal is a hydrated amorphous form of silica (SiO2·''n''H2O); its water content may range from 3 to 21% by weight, but is usually between 6 and 10%. Due to its amorphous property, it is classified as a mineraloid, unlike crystalline forms ...

named for the phenomenon as plot devices * William S. Burroughs's 1981 novel ''

Cities of the Red Night ''Cities of the Red Night'' is a 1981 novel by American author William S. Burroughs. His first full-length novel since '' The Wild Boys'' (1971), it is part of his final trilogy of novels, known as The Red Night Trilogy, followed by ''The Place of ...

'' *

Elizabeth Wein Elizabeth E. Wein (, born October 2, 1964) is an American-born writer best known for her young adult historical fiction. She holds both American and British citizenship. Personal life Elizabeth E. Wein was born in New York City on October 2, ...

's 2012 novel ''

Code Name Verity ''Code Name Verity'' is a young adult historical fiction novel by Elizabeth Wein that was published in 2012. It focuses on the friendship between two young British women, one English and one Scottish, in World War II – a spy captured by the N ...

'' *''The Green Ray'', a piece of orchestral music composed by Gavin Bryars and first performed in 1991 * Carl Hiaasen's 2005 young adult novel '' Flush'' features a green flash throughout the plot *'' Pirates of the Caribbean: At World's End'', a 2007 film that features green flashes as a plot point, as pirate folklore holds that it's a signal that a soul has come back from the dead. *The Lightbringer Series by US fantasy author

Brent Weeks Brent Weeks (born March 7, 1977) is an American fantasy writer. His debut novel, ''The Way of Shadows'', was a ''New York Times'' best seller in April 2009. Each of the five books in his Lightbringer Series made the NYT list as well, starting w ...

mentions the green flash throughout, with characters calling it "Orholam's Wink." *The 2012 television movie '' Blue Lagoon: The Awakening'' features a green flash when Emma and Dean are watching the sunset on the island they are stranded on. *

Pokémon (an abbreviation for in Japan) is a Japanese media franchise managed by The Pokémon Company, founded by Nintendo, Game Freak, and Creatures (company), Creatures, the owners of the trademark and copyright of the franchise. In terms of ...

Sun & Moon Anime "Rising from the Ruins!" Episode 982 - Ash's Rockruff evolves into Lycanroc as the green flash occurs at dusk and reveals a new Lycanroc type up until then unknown (Dusk Form). *

Margaret Wise Brown Margaret Wise Brown (May 23, 1910 – November 13, 1952) was an American writer of children's books, including ''Goodnight Moon'' and ''The Runaway Bunny'', both illustrated by Clement Hurd. She has been called "the laureate of the nursery" for ...

's poem The Secret Song which describes "the first green light of the sun". *Artist

Tacita Dean Tacita Charlotte Dean CBE, RA (born 1965) is a British / German visual artist who works primarily in film. She was a nominee for the Turner Prize in 1998, won the Hugo Boss Prize in 2006, and was elected to the Royal Academy of Arts in 2008. S ...

's moving image work 'The Green Ray'

References

External links

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

explanations and image gallery, Les Cowley's Atmospheric Optics site *
06/03/2010 Photograph of a green flash over the Indian OceanGreen Flash Videos
{{DEFAULTSORT:Green Flash Atmospheric optical phenomena Solar phenomena Sky