# Moonbow

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{{For|the 1983 Soviet science fiction film|Moon Rainbow}}
{{short description|Rainbow produced by moonlight rather than sunlight}}
A '''moonbow''' (also known as a '''moon rainbow''' or '''lunar rainbow''') is a [rainbow](/source/rainbow) produced by [moonlight](/source/moonlight) rather than direct [sunlight](/source/sunlight). Other than the difference in the light source, its formation is the same as for a solar rainbow: It is caused by the [refraction](/source/refraction) of light in many water droplets, such as a rain shower or a waterfall, and is always positioned in the opposite part of the sky from the Moon relative to the observer.<ref name=":0">{{Cite web |title=Moonbow |url=https://www.metoffice.gov.uk/weather/learn-about/weather/optical-effects/rainbows/moonbow |access-date=2023-06-14 |website=Met Office |language=en}}</ref>
[[File:Moonbow, Kula, Hawaii..jpg|thumbnail|Lunar rainbow over [Kihei](/source/Kihei%2C_Hawaii), [Maui](/source/Maui), Hawaii, US]]
Moonbows are much fainter than solar rainbows, due to the smaller amount of light reflected from the surface of the [Moon](/source/Moon). Because the light is usually too faint to excite the [cone color receptors](/source/Cone_cell) in human eyes, it is difficult for the human eye to discern colors in a moonbow. As a result, a moonbow often appears to be white.<ref>{{cite web
| last=Walklet | first=Keith S. | year=2006
| url=http://www.anseladams.com/content/newsletter/lunar_rainbow.html
| title=Lunar Rainbows&nbsp;– When to View and How to Photograph a "Moonbow"
| publisher=The Ansel Adams Gallery
| accessdate=2007-07-09 |archiveurl = https://web.archive.org/web/20070624175822/http://www.anseladams.com/content/newsletter/lunar_rainbow.html <!-- Bot retrieved archive --> |archivedate = 2007-06-24}}</ref> However, the colors in a moonbow do appear in [long exposure photographs](/source/Long-exposure_photography).

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==True moonbows==
thumb|300px|Photograph of a real moonbow spanning over the castle of Wernigerode, Germany
By definition,{{citation needed|reason=Whose definition? Sources please.|date=February 2015}} true moonbows are associated with atmospheric rain events and arise at a time when conditions are optimal in terms of levels of reflected solar light being reflected from the Moon's surface.  All true moonbows are therefore short-lived and transitory in nature. True moonbows are independent of all terrestrially fixed geographical features such as waterfalls for their existence.
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Moonbows have been mentioned at least since [Aristotle's](/source/Aristotle) [''Meteorology''](/source/Meteorology_(Aristotle)) (circa 350 BC), and are associated with the ancient Greek lunar goddess, [Selene](/source/Selene).

==Viewing==

Moonbows are most easily viewed when the Moon is at or nearest to its brightest phase [full moon](/source/full_moon).  For moonbows to have the greatest prospect of appearing, the Moon must be low in the sky (at an elevation of less than 42 degrees, preferably lower) and must not be obscured by cloud. In addition, the night sky must be very dark.  Since the sky is not completely dark on a rising/setting full moon, this means they can only be observed two to three hours before sunrise (a time with few observers), or two to three hours after sunset. And, of course, there must be water droplets (e.g. from rain or spray) opposite the Moon.<ref name=":0" /> This combination of requirements makes moonbows much rarer than rainbows produced by the daytime sunlight.  Moonbows may also be visible when rain falls during full moonrise at extreme latitudes during the winter months when the prevalence of the hours of darkness gives more opportunity for the phenomenon to be observed.<ref>{{Cite web |last=Miller |first=James |date=2018-05-28 |title=Examining the Phenomenon of Lunar Rainbows |url=https://www.astronomytrek.com/examining-the-phenomenon-of-lunar-rainbows/ |access-date=2023-06-14 |language=en-US}}</ref>

It is said that the definition of the colours depends upon the size of the moisture drops present in the air: the smaller they are the less vivid the colours. Below 1/500 inch diameter they usually refract more or less white light as the component colours are merged. <ref>Valerie Porter, “The Second Field Book of Country Queries” p. 89</ref> 

<!-- Hiding this passage until reliable sources on "true" vs. "false" moonbows are provided. Please see the discussion page. ~~~~

==False moonbows==
[[File:Partial corona formed by moonlight illuminating a cloud (2011-12-08).jpg|180px|thumb|'''Not a moonbow'''—partial [corona](/source/Corona_(optical_phenomenon)) formed by moonlight diffracted by droplets in a cloud]]

A colored circle around the Moon is not a moonbow.  It is usually a [22° halo](/source/22%C2%B0_halo) produced by refraction through hexagonal ice crystals in a cirrus cloud. Colored rings close to the moon are a [corona](/source/Corona_(optical_phenomenon)), a diffraction phenomenon produced by minuscule water droplets or ice crystals in clouds.

Spray, mist or fog related bows are classified as false moonbows.{{citation needed|reason=By whom? Sources please.|date=February 2015}} Such false bows (particularly waterfall spray bows) are dependent on geographical features. Moreover, since the same 'spray bow'  is very often visible & reproducible in daylight hours, it means that such a bow cannot be linked exclusively to the effect of moonlight.

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===Locations===
[[File:Moonbow at lower Yosemite fall.jpg|thumb|Spray moonbow at the Lower [Yosemite Fall](/source/Yosemite_Falls)]] 

Numerous places in the world feature spray-, fog- or mist-induced bows. In the United States such bows may be seen in relation to various waterfalls including [Niagara Falls](/source/Niagara_Falls), New York,<ref>{{Cite web|url=https://www.niagarafallstourism.com/blog/goat-island-and-luna-island-how-did-they-get-their-names/|title=Goat Island and Luna Island How Did they get The…|website=Niagara Falls Canada|accessdate=17 December 2020|archive-date=17 April 2022|archive-url=https://web.archive.org/web/20220417033321/https://www.niagarafallstourism.com/blog/goat-island-and-luna-island-how-did-they-get-their-names/|url-status=dead}}</ref> [Yosemite National Park](/source/Yosemite_National_Park), California<ref>{{cite news|title='Moonbows,' Lunar Rainbows, Visible At Yosemite National Park (VIDEO)|url=http://www.huffingtonpost.com/2011/07/15/moonbows-lunar-rainbows-yosemite_n_900052.html|publisher=Huffington Post—Green Blog|accessdate=22 December 2012|date=15 July 2011}}</ref> and [Cumberland Falls](/source/Cumberland_Falls), near [Corbin](/source/Corbin%2C_Kentucky), Kentucky.<ref name=bailey>{{cite book |last=Bailey |first=Bill |title=Kentucky State Parks |publisher=Glovebox Guidebooks of America |location=[Saginaw, Michigan](/source/Saginaw%2C_Michigan) |year=1995 |isbn=978-1-881139-13-3 |chapter=Cumberland Falls State Resort Park}}</ref><ref>{{cite book | last1 = Manning | first1 = Russ | title = The Historic Cumberland Plateau: An Explorer's Guide | page = 106 | url = https://books.google.com/books?id=ZtfyLnSBF8sC&q=moonbow | accessdate = 2011-10-28 | isbn = 978-1-57233-044-3| year = 1999 | publisher = Univ. of Tennessee Press }}</ref> [Victoria Falls](/source/Victoria_Falls%2C_Zambia), on the border between Zambia and Zimbabwe is also widely known for spray moonbows.<ref>{{cite web|title=A Lunar Rainbow A Wonderful Sight Not To Be Missed...…|url=http://www.victoriafalls-guide.net/lunar-rainbow.html|website=Victoria Falls Activities|publisher=Victoria Falls Travel Guide|accessdate=22 December 2012}}</ref>   

Spray moonbows are also seen with some regularity in the [cloud forests](/source/cloud_forests) of Costa Rica, in mountain towns like Monteverde and Santa Elena.  These occur when clouds of mist are blown in from the Caribbean by the [Christmas Winds](/source/Christmas_Winds).  The Christmas Winds happen from the end of December through late January or early February.  These clouds of mists create a streaming pattern of stripes giving rise to their popular name in Spanish,  ''pelo de gato'' ("cat's hair). Moonbows happen in this part of Costa Rica almost every full moon in the months of December through February.  The bows that are caused by Pelo de Gato are not limited to just before dawn but can happen after sunset too, but it does need a full or nearly full moon.

Moonbows are also found in wet regions of Hawaii, such as [Kauai](/source/Kauai) (with the moon rising in the east during light rain) and the [Big Island](/source/Hawaii_(island)) of Hawaii.<ref>{{cite news|title=Photographer captures moonbow over Waimea|url=http://www.hawaiinewsnow.com/story/18698752/photographer-captures-moonbow-over-waimea|accessdate=22 December 2012|newspaper=Hawaii News Now|date=June 4, 2012}}</ref>

==References==
{{reflist}}

==External links==
* [https://web.archive.org/web/20100623015523/http://www.mauimagazine.net/Maui-Magazine/May-June-2010/Maui-rsquos-Night-Sky/  "Maui's Night Sky"] Time elapse photography by Wally Pacholka. ''[Maui No Ka 'Oi Magazine](/source/Maui_No_Ka_'Oi_Magazine)'' Vol.14, No.3 (May 2010)
* [http://calvinbradshaw.smugmug.com/gallery/3469956_FNwaQ#195155730_eFhnx/ Lunar Rainbow photos from Victoria Falls]
* [https://web.archive.org/web/20080421035300/http://www.atoptics.co.uk/rainbows/moonbow.htm Moonbow picture]

Category:Atmospheric optical phenomena
Category:Lunar science
Category:Rainbow

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Adapted from the Wikipedia article [Moonbow](https://en.wikipedia.org/wiki/Moonbow) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Moonbow?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.