Rainbow: Difference between revisions - Wikipedia

Tag: Reverted

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A rainbow is not located at a specific distance from the observer, but comes from an optical illusion caused by any water droplets viewed from a certain angle relative to a light source. Thus, a rainbow is not an object and cannot be physically approached. Indeed, it is impossible for an observer to see a rainbow from water droplets at any angle other than the customary one of 42 degrees from the direction opposite the light source. Even if an observer sees another observer who seems "under" or "at the end of" a rainbow, the second observer will see a different rainbow—farther off—at the same angle as seen by the first observer.

Rainbows span a continuous spectrum of colours. Any distinct bands perceived are an artefact of human [[color vision|colour vision]], and no banding of any type is seen in a black-and-white photo of a rainbow, only a smooth gradation of intensity to a maximum, then fading towards the other side. For colours seen by the human eye, the most commonly cited and remembered sequence is [[Isaac Newton]]'s sevenfold red, orange, yellow, green, blue, [[indigo]] and violet,<ref name="Newton1740" />{{efn|"A careful reading of Newton’s work indicatesinduuates that the colorcolour he called indigo, we would normally call blue; his blue is then what we would name blue-green or cyan."<ref name=Waldman2002>{{cite book|url=https://books.google.com/books?id=PbsoAXWbnr4C&dq=%22the+color+he+called+indigo%22&pg=RA1-PA193|last1=Waldman|first1=Gary|title=Introduction to Light: The Physics of Light, Vision, and Color|date=1983|page=193|edition=2002 revised|publisher=[[Dover Publications]]|location=Mineola, New York|isbn=978-0486421186}}</ref>}} remembered by the [[mnemonic]] ''Richard Of York Gave Battle In Vain'' ([[ROYGBIV]]). The initialism is sometimes referred to in reverse order, as VIBGYOR.

Rainbows can be caused by many forms of airborne water. These include not only rain, but also mist, spray, and airborne [[dew]].

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== {{Anchor|The seven colours of the rainbow}}Number of colours in a spectrum or a rainbow ==

A [[spectrum]] obtained using a glass prism and a point source is a continuum of wavelengths without bands. The number of colours that the human eye is able to distinguish in a spectrum is in the order of 100.<ref>{{cite web|url=http://www.pburch.net/dyeing/dyeblog/C128544578/E1447734446/|last=Burch|first=Paula E.|title=All About Hand Dyeing Q&A|access-date=27 August 2012|url-status=live|archive-url=https://web.archive.org/web/20120424174853/http://www.pburch.net/dyeing/dyeblog/C128544578/E1447734446/|archive-date=24 April 2012}} (A number between 36 and 360 is in the order of 100)</ref> Accordingly, the [[Munsell color system|Munsell colour system]] (a 20th-century system for numerically describing colours, based on equal steps for human visual perception) distinguishes 100 hues. The apparent discreteness of main colours is an artefact of human perception and the exact number of main colours is a somewhat arbitrary choice.

Newton, who admitted his eyes were not very critical in distinguishing colours,<ref>{{Cite book |url=https://books.google.com/books?id=EU74cB7kMMsC&pg=PA140|title=Color and Meaning|last=Gage |first=John |year=1994|publisher=University of California Press|isbn=978-0-520-22611-1|page=140}}</ref> originally (1672) divided the spectrum into five main colours: red, yellow, green, blue and violet. Later he included orange and indigo, giving seven main colours by analogy to the number of notes in a musical scale.<ref name="Newton1740">Isaac Newton, ''Optice: Sive de Reflexionibus, Refractionibus, Inflexionibus & Coloribus Lucis Libri Tres,'' Propositio II, Experimentum VII, edition 1740</ref>{{efn|"Ex quo clarissime apparet, lumina variorum colorum varia esset refrangibilitate : idque eo ordine, ut color ruber omnium minime refrangibilis sit, reliqui autem colores, aureus, flavus, viridis, cæruleus, indicus, violaceus, gradatim & ex ordine magis magisque refrangibiles."<ref name="Newton1740" />}}<ref>{{cite web|url=http://www1.umn.edu/ships/updates/newton1.htm |title=Newton's Colors |last=Allchin |first=Douglas |website=SHiPS Resource Center |access-date=2010-10-16 |url-status=dead |archive-url=https://web.archive.org/web/20140929225102/http://www1.umn.edu/ships/updates/newton1.htm |archive-date=2014-09-29 }}</ref> Newton chose to divide the visible spectrum into seven colours out of a belief derived from the beliefs of the [[Ancient Greece|ancient Greek]] [[sophist]]s, who thought there was a connection between the colours, the musical notes, the known objects in the [[Solar System]], and the days of the week.<ref>{{cite web |url=http://www.colourmusic.info/opticks3.htm |title=Music For Measure: On the 300th Anniversary of Newton's ''Opticks'' |access-date=2017-04-07 |last=Hutchison |first=Niels |year=2004 |website=Colour Music |url-status=live |archive-url=https://web.archive.org/web/20170118041157/http://www.colourmusic.info/opticks3.htm |archive-date=2017-01-18 }}</ref><ref>{{cite book |last=Newton |first=Isaac |author-link=Isaac Newton |title=Opticks |year=1704 |title-link=Opticks }}</ref><ref>"Visible Spectrum Wikipedia Contributors, Wikipedia, The Free Encyclopedia accessed 11/17/2013 available at: [[Visible spectrum]]</ref> Scholars have noted that what Newton regarded at the time as "blue" would today be regarded as [[cyan]], and what Newton called "indigo" would today be considered [[blue]].<ref name="Waldman2002" />

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Rainbows occur frequently [[Rainbows in mythology|in mythology]], and have been used in the arts. One of the earliest literary occurrences of a rainbow is in the [[Book of Genesis]] chapter 9, as part of the flood story of [[Noah]], where it is a sign of God's covenant to never destroy all life on Earth with a global flood again. In [[Norse mythology]], the rainbow bridge [[Bifröst]] connects the world of men ([[Midgard]]) and the realm of the gods ([[Asgard]]). [[Cuchavira]] was the god of the rainbow for the [[Muisca]] in present-day [[Colombia]] and when the regular rains on the [[Bogotá savanna]] were over, the people thanked him offering [[gold]], [[snail]]s and small [[emerald]]s. Some forms of [[Tibetan Buddhism]] or [[Dzogchen]] reference a [[rainbow body]].<ref>{{cite book |author-link=Reginald Ray|last=Ray|first=Reginald|title=Secret of the Vajra World: The Tantric Buddhism of Tibet|url=https://www.google.com/books/edition/Secret_of_the_Vajra_World/kQMLAAAAYAAJ?hl=en&gbpv=0|publisher=[[Shambhala Publications]]|year=2001|page=323|isbn=9781570627729}}</ref> The Irish [[leprechaun]]'s secret hiding place for his pot of gold is usually said to be at the end of the rainbow. This place is appropriately impossible to reach, because the rainbow is an optical effect which cannot be approached.

Rainbows appear in heraldry - in heraldry the rainbow proper consists of 4 bands of colorcolour ([[Or (heraldry)|Or]], [[Gules]], [[Vert (heraldry)|Vert]], [[Argent]]) with the ends resting on clouds.<ref>{{citation| url = https://mistholme.com/dictionary/rainbow/ | title = Rainbow | work = mistholme.com}}</ref> Generalised examples in coat of arms include those of the towns of [[Regen]] and [[Pfreimd]], both in Bavaria, Germany; and of [[Bouffémont]], France; and of the [[69th Infantry Regiment (New York)]] of the [[Army National Guard]] (USA).

[[Rainbow flag]]s have been used for centuries. It was a symbol of the Cooperative movement in the [[German Peasants' War]] in the 16th century, of peace in Italy, and of [[gay pride]] and [[LGBT social movements]] since the 1970s. In 1994, Archbishop [[Desmond Tutu]] and President [[Nelson Mandela]] described newly democratic post-[[apartheid]] South Africa as the [[rainbow nation]]. The rainbow has also been used in technology product logos, including the [[Apple Inc.|Apple computer]] logo. Many political alliances spanning multiple political parties have called themselves a "[[Rainbow Coalition (disambiguation)|Rainbow Coalition]]".

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* [https://www.youtube.com/watch?v=BU1n0mtB1xs Creating Circular and Double Rainbows!] – video explanation of basics, shown artificial rainbow at night, second rainbow and circular one.

{{ColorColour topics}}

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