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Moonbow

Moonbow

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A moonbow is a rainbow
Rainbow
A rainbow is an optical and meteorological phenomenon that causes a spectrum of light to appear in the sky when the Sun shines on to droplets of moisture in the Earth's atmosphere. It takes the form of a multicoloured arc...

 produced by light reflected off the surface of the moon rather than from direct sunlight. Moonbows are relatively faint, due to the smaller amount of light reflected from the surface of the moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

. They are always in the opposite part of the sky from the moon.

It is difficult for the human eye to discern colors in a moonbow because the light is usually too faint to excite the cone color receptors in human eyes. As a result, they often appear to be white. However, the colors in a moonbow do appear in long exposure photographs.

True moonbows


A true moonbow is lit from the Moon itself. A colored rainbow when the sun is setting or when it is darker out is not a moonbow because it is still produced by sunlight. Moonbows have been mentioned at least since Aristotle
Aristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...

, in his Meteorology, circa 350 BC, and in 1847; , and the term moonbow was used by Nick Whelan who sighted one of the first documented moonbows in Eastern Utah.

Faux moonbows


A colored circle around the moon is not a moonbow—it is usually a 22° halo
22° halo
A 22° halo is a halo, one type of optical phenomenon, forming a circle 22° around the sun, or occasionally the moon. It forms as sunlight is refracted in hexagonal ice crystals suspended in the atmosphere...

 produced by refraction through hexagonal ice crystals in cirrus cloud. Colored rings close to the moon are a corona, a diffraction phenomenon produced by very small water droplets or ice crystals in clouds.

Viewing


Moonbows are most easily viewed when the moon is near to full (when it is brightest). For true moonbows, other than those produced by waterfalls or sprays, the moon must be low in the sky (less than 42 degrees and preferably lower) and the sky must be dark. And of course there must be rain falling opposite the moon. This combination of requirements makes moonbows much more rare than rainbows produced by the sun.

Notable spray moonbow locations



Few places in the world frequently feature this phenomenon. Several waterfalls in Yosemite National Park
Yosemite National Park
Yosemite National Park is a United States National Park spanning eastern portions of Tuolumne, Mariposa and Madera counties in east central California, United States. The park covers an area of and reaches across the western slopes of the Sierra Nevada mountain chain...

. Cumberland Falls
Cumberland Falls
Cumberland Falls, sometimes called the Little Niagara, the Niagara of the South, or the Great Falls, is a large waterfall on the Cumberland River in southeastern Kentucky...

, near Corbin
Corbin, Kentucky
- Economy :Originally formed by L&N Railroad, rail transport was the backbone of the local economy in the first half of the twentieth century. While the railroad continues to play an important role, the decline of the rail industry in the latter half of the twentieth century, as well as the loss...

, Kentucky
Kentucky
The Commonwealth of Kentucky is a state located in the East Central United States of America. As classified by the United States Census Bureau, Kentucky is a Southern state, more specifically in the East South Central region. Kentucky is one of four U.S. states constituted as a commonwealth...

, U.S.A.
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 and Victoria Falls
Victoria Falls
The Victoria Falls or Mosi-oa-Tunya is a waterfall located in southern Africa on the Zambezi River between the countries of Zambia and Zimbabwe.-Introduction:...

 on the border between Zambia
Zambia
Zambia , officially the Republic of Zambia, is a landlocked country in Southern Africa. The neighbouring countries are the Democratic Republic of the Congo to the north, Tanzania to the north-east, Malawi to the east, Mozambique, Zimbabwe, Botswana and Namibia to the south, and Angola to the west....

 and Zimbabwe
Zimbabwe
Zimbabwe is a landlocked country located in the southern part of the African continent, between the Zambezi and Limpopo rivers. It is bordered by South Africa to the south, Botswana to the southwest, Zambia and a tip of Namibia to the northwest and Mozambique to the east. Zimbabwe has three...

 are widely known for moonbow occurrence. Also Waimea on Hawaii's Kauai Island. A moonbow sighting occurred on July 26, 2010 at Kalapana on the island of Hawaii (the Big island), seen from near the active lava flow.

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