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A moonbow (also known as a moon rainbow or lunar rainbow) is a rainbow produced by
moonlight Moonlight consists of mostly sunlight (with little earthlight) reflected from the parts of the Moon's surface where the Sun's light strikes. Illumination The intensity of moonlight varies greatly depending on the lunar phase, but even the ful ...
rather than direct
sunlight Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when t ...
. Other than the difference in the light source, its formation is the same as for a solar rainbow: It is caused by the 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. Moonbows are much fainter than solar rainbows, due to the smaller amount of light reflected from the surface of the Moon. Because the light is usually too faint to excite the cone color receptors 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. However, the colors in a moonbow do appear in long exposure photographs. Moonbows have been mentioned at least since
Aristotle's Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of phil ...
''Meteorology'' (circa 350 BC).


Viewing

Moonbows are most easily viewed when the Moon is at or nearest to its brightest phase 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. 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. 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.


Locations

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,
New York New York most commonly refers to: * New York City, the most populous city in the United States, located in the state of New York * New York (state), a state in the northeastern United States New York may also refer to: Film and television * '' ...
, Yosemite National Park, California and Cumberland Falls, near
Corbin Corbin may refer to: People * Corbin (given name) * Corbin (surname) * Corbin (musician), American singer Buildings * Corbin Building, a historic building located at 192 Broadway in New York, US * Corbin Cabin, a log structure in Shenandoah ...
, Kentucky. Victoria Falls, on the border between Zambia and Zimbabwe is also widely known for spray moonbows. Spray moonbows are also seen with some regularity in the
cloud forests A cloud forest, also called a water forest, primas forest, or tropical montane cloud forest (TMCF), is a generally tropical or subtropical, evergreen, montane, moist forest characterized by a persistent, frequent or seasonal low-level cloud ...
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 Christmas is an annual festival commemorating the birth of Jesus Christ, observed primarily on December 25 as a religious and cultural celebration among billions of people around the world. A feast central to the Christian liturgical year, ...
. 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
Kauai Kauai, () anglicized as Kauai ( ), is geologically the second-oldest of the main Hawaiian Islands (after Niʻihau). With an area of 562.3 square miles (1,456.4 km2), it is the fourth-largest of these islands and the 21st largest island ...
, Hawaii, with the moon rising in the east during light rain. Similar bows are occasionally seen from the Big Island of Hawaii.


See also

* Moon ring * Moon dog


References


External links

{{linkfarm, date=March 2016
"Maui's Night Sky"
Time elapse photography by Wally Pacholka. '' Maui No Ka 'Oi Magazine'' Vol.14, No.3 (May 2010)
Lunar Rainbow photos from Victoria Falls





Zambezi Guide on taking photos of Lunar Rainbows from Victoria Falls



Moonbow photo at Brandywine Falls, Whistler, Canada

Moving rainbow over Patagonia, all night time-lapse movie

Kentucky State Park Moonbow Dates
At the bottom of the page under the "Moonbow" tab
Moon Light Effects: Moon Rings, Moon Dogs And Other Moon Light Phenomena...Moonbow on Big Island Hawaii
*https://moon-lamp.co.uk/ Atmospheric optical phenomena Moon Rainbow