The green flash and green ray are

meteorological Meteorology is the scientific study of the Earth's atmosphere and short-term atmospheric phenomena (i.e. weather), with a focus on weather forecasting. It has applications in the military, aviation, energy production, transport, agriculture ...

optical phenomena Optical phenomena are any observable events that result from the interaction of light and matter. All optics, optical phenomena coincide with Quantum mechanics, quantum phenomena. Common optical phenomena are often due to the interaction of ligh ...

that sometimes occur transiently around the moment of

sunset Sunset (or sundown) is the disappearance of the Sun at the end of the Sun path, below the horizon of the Earth (or any other astronomical object in the Solar System) due to its Earth's rotation, rotation. As viewed from everywhere on Earth, it ...

sunrise Sunrise (or sunup) is the moment when the upper rim of the Sun appears on the horizon in the morning, at the start of the Sun path. The term can also refer to the entire process of the solar disk crossing the horizon. Terminology Although the S ...

. When the conditions are right, a distinct green spot is briefly visible above the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

'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, t ...

; 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 composed of a layer of gas mixture that surrounds the Earth's planetary surface (both lands and oceans), known collectively as air, with variable quantities of suspended aerosols and particulates (which create weathe ...

can cause the light from the Sun to separate, via wavelength varying

refraction In physics, refraction is the redirection of a wave as it passes from one transmission medium, 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 commo ...

, 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 curve 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 curve divides all viewing directions based on whethe ...

, 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 Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

and bright planets at the horizon, including

Venus Venus is the second planet from the Sun. It is often called Earth's "twin" or "sister" planet for having almost the same size and mass, and the closest orbit to Earth's. While both are rocky planets, Venus has an atmosphere much thicker ...

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 Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

. 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 Aircraft flight control system, directional flight controls. Some other aircrew, aircrew members, such as navigators or flight engineers, are al ...

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 The Vatican Observatory () is an astronomical research and educational institution supported by the Holy See. Originally based in the Roman College of Rome, the Observatory is now headquartered in Castel Gandolfo, Italy and operates a telescope a ...

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 gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...

causes 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 phenome ...

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

. 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. With slight

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

, 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. While simple atmospheric refraction or lensing explains the background gradient of red-amber twilight, the primary potential cause of the bright, verdant discontinuity from that gradient known as the Green Flash may be due to naturally-occurring coherent (laser) light. Part of this phenomenon was recently discovered by researchers at the

Washington University School of Medicine Washington University School of Medicine (WashU Medicine) is the medical school of Washington University in St. Louis, located in the Central West End neighborhood of St. Louis, Missouri. Founded in 1891, the School of Medicine shares a ca ...

, regarding infrared-laser light converting-up (or upconverting) to visible-green laser light, causing what researchers there call "a double hit" of photons on the retina, creating the perception of bright neon green from an originally invisible infrared laser. Doubling the wavelength of green light yields roughly 1000-1100 nm infrared light, so the most likely hypothesis is that the Green Flash is coherent upconverted infrared (laser) light that "double-hits" the retina or camera lens, creating the effect of bright green (additionally, this explains why the Green Flash is also sometimes blue or purple; coherent infrared light can upconvert to any color of visible light if the conditions are met).

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 influenc ...

, or at distant

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

s), are not understood.

Blue flashes

On rare occasion, the amount of blue light is sufficient to be visible as a "blue flash".

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 within the observable universe. In astronomy, the terms ''object'' and ''body'' are of ...

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

, which works as a

prism PRISM is a code name for a program under which the United States National Security Agency (NSA) collects internet communications from various U.S. internet companies. The program is also known by the SIGAD . PRISM collects stored internet ...

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 A pollutant or novel entity is a substance or energy introduced into the environment that has undesired effect, or adversely affects the usefulness of a resource. These can be both naturally forming (i.e. minerals or extracted compounds like oi ...

as they spread throughout an increasing volume of atmosphere. 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 Richard Evelyn Byrd Jr. (October 25, 1888 – March 11, 1957) was an American naval officer, and pioneering aviator, polar explorer, and organizer of polar logistics. Aircraft flights in which he served as a navigator and expedition leader cr ...

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. 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 (electromagnetic radiation), absorption, or Reflection (physics), reflection of electromagnetic radiation. Originally, it was an optical instrument using len ...

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'', mean ...

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'' helped to popularize the green flash phenomenon. The disappearance of an opal, named the "Green Flash at Sunset" for the scientific phenomenon, forms a significant point plot in Victoria Holt's 1976 novel '' The Pride of the Peacock''. The actual phenomenon is referenced several times in the text. In the 1984 film The Island Closest to Heaven Yuichi Fukaya took Mari, the main character to watch the sunset and told about the green flash after the sun sinks into the sea. According to him those people who saw it will be able to find what they are for looking for. In Éric Rohmer's 1986 film '' The Green Ray'' (French: ''Le rayon vert''), the main character, Delphine, eavesdrops on a conversation about Jules Verne's novel and the significance of the green flash, eventually witnessing the phenomenon herself in the final scene. In "Arthur's New Year's Eve" from the first season of ''

Arthur Arthur is a masculine given name of uncertain etymology. Its popularity derives from it being the name of the legendary hero King Arthur. A common spelling variant used in many Slavic, Romance, and Germanic languages is Artur. In Spanish and Ital ...

'' in 1996, Arthur Read, having never stayed up until midnight on New Year's Eve before, talks with his friends about what happens when the New Year comes. Despite not actually having stayed up themselves, they each share their take on the matter, Prunella Deegan telling him that there is an amazing green flash at midnight, but if it doesn't happen, then it has to stay the same year for another whole year. In 2002, the

City of San Diego San Diego ( , ) is a city on the Pacific coast of Southern California, adjacent to the Mexico–United States border. With a population of over 1.4 million, it is the List of United States cities by population, eighth-most populous city in t ...

installed an art piece titled "The Green Flash" by Malcolm Jones next to the beach boardwalk in Mission Beach. The acrylic and concrete work also includes a plaque that describes the scientific phenomenon.

Walt Disney Pictures Walt Disney Pictures is an American film Film production company, production company and subsidiary of Walt Disney Studios (division), the Walt Disney Studios, a division of Disney Entertainment, which is owned by the Walt Disney Company. The st ...

' 2007 movie '' Pirates of the Caribbean: At World's End'' references the green flash as a signal that a soul had returned from the dead. The episode ''Trials and Determinations!'' of Pokémon the Series: Sun & Moon references the green flash when Ash's Rockruff evolves into Dusk Form Lycanroc after witnessing a green flash at sunset.

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