Moonbow

Last updated
Photograph of a spray-induced moonbow (lunar rainbow) at Victoria Falls (Zambia side) Lunar Rainbow 3 - ORION L - Victoria Falls - Calvin Bradshaw 3.jpg
Photograph of a spray-induced moonbow (lunar rainbow) at Victoria Falls (Zambia side)

A moonbow (also known as a moon rainbow or lunar rainbow) is a rainbow produced by moonlight rather than direct 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 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. [1]

Contents

Lunar rainbow over Kihei, Maui, Hawaii, US Moonbow, Kula, Hawaii..jpg
Lunar rainbow over Kihei, Maui, Hawaii, US

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. [2] However, the colors in a moonbow do appear in long exposure photographs.

Moonbows have been mentioned at least since Aristotle's 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. [1] 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. [3]

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. [4]

Locations

Spray moonbow at the Lower Yosemite Fall Moonbow at lower Yosemite fall.jpg
Spray moonbow at the Lower Yosemite Fall

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, [5] Yosemite National Park, California [6] and Cumberland Falls, near Corbin, Kentucky. [7] [8] Victoria Falls, on the border between Zambia and Zimbabwe is also widely known for spray moonbows. [9]

Spray moonbows are also seen with some regularity in the 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. 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 (with the moon rising in the east during light rain) and the Big Island of Hawaii. [10]

Related Research Articles

<span class="mw-page-title-main">Lunar eclipse</span> Astronomical event

A lunar eclipse is an astronomical event that occurs when the Moon moves into the Earth's shadow, causing the Moon to be darkened. Such an alignment occurs during an eclipse season, approximately every six months, during the full moon phase, when the Moon's orbital plane is closest to the plane of the Earth's orbit.

<span class="mw-page-title-main">Cumberland Falls</span> Waterfall in the U.S. state of Kentucky

Cumberland Falls, sometimes called the Little Niagara, the Niagara of the South, or the Great Falls, is a waterfall on the Cumberland River in southeastern Kentucky. Spanning the river at the border of McCreary and Whitley counties, the waterfall is the central feature of Cumberland Falls State Resort Park and is part of the Office of Kentucky Nature Preserves designated Wild River System.

<span class="mw-page-title-main">Sky</span>

The sky is an unobstructed view upward from the surface of the Earth. It includes the atmosphere and outer space. It may also be considered a place between the ground and outer space, thus distinct from outer space.

<span class="mw-page-title-main">Mist</span> Phenomenon caused by small droplets of water suspended in air

Mist is a phenomenon caused by small droplets of water suspended in the cold air, usually by condensation. Physically, it is an example of a dispersion. It is most commonly seen where water vapor in warm, moist air meets sudden cooling, such as in exhaled air in the winter, or when throwing water onto the hot stove of a sauna. It can be created artificially with aerosol canisters if the humidity and temperature conditions are right. It can also occur as part of natural weather, when humid air cools rapidly, notably when the air comes into contact with surfaces that are much cooler than the air.

<span class="mw-page-title-main">Glory (optical phenomenon)</span> Optical phenomenon that resembles an iconic saints halo about the shadow of the observers head

A glory is an optical phenomenon, resembling an iconic saint's halo around the shadow of the observer's head, caused by sunlight or moonlight interacting with the tiny water droplets that comprise mist or clouds. The glory consists of one or more concentric, successively dimmer rings, each of which is red on the outside and bluish towards the centre. Due to its appearance, the phenomenon is sometimes mistaken for a circular rainbow, but the latter has a much larger diameter and is caused by different physical processes.

<span class="mw-page-title-main">Halo (optical phenomenon)</span> Optical phenomenon of the sky

A halo is an optical phenomenon produced by light interacting with ice crystals suspended in the atmosphere. Halos can have many forms, ranging from colored or white rings to arcs and spots in the sky. Many of these appear near the Sun or Moon, but others occur elsewhere or even in the opposite part of the sky. Among the best known halo types are the circular halo, light pillars, and sun dogs, but many others occur; some are fairly common while others are extremely rare.

<span class="mw-page-title-main">Brocken spectre</span> Atmospheric optical phenomenon

A Brocken spectre, also called Brocken bow, mountain spectre, or spectre of the Brocken is the magnified shadow of an observer cast in mid air upon any type of cloud opposite a strong light source. The figure's head can be surrounded by a bright area called Heiligenschein, or halo-like rings of rainbow-coloured light forming a glory, which appear opposite the Sun's direction when uniformly sized water droplets in clouds refract and backscatter sunlight.

<span class="mw-page-title-main">Corona (optical phenomenon)</span> Optical phenomenon of the sky

In meteorology, a corona is an optical phenomenon produced by the diffraction of sunlight or moonlight by individual small water droplets and sometimes tiny ice crystals of a cloud or on a foggy glass surface. In its full form, a corona consists of several concentric, pastel-colored rings around the celestial object and a central bright area called an aureole. The aureole is often the only visible part of the corona and has the appearance of a bluish-white disk which fades to reddish-brown towards the edge. The angular diameter of a corona depends on the sizes of the water droplets involved; smaller droplets produce larger coronae. For the same reason, the corona is the most pronounced when the size of the droplets is most uniform. Coronae differ from halos in that the latter are formed by refraction from comparatively large rather than small ice crystals. The diffraction pattern is called an Airy disk.

<span class="mw-page-title-main">Rainbow</span> Meteorological phenomenon

A rainbow is an optical phenomenon caused by refraction, internal reflection and dispersion of light in water droplets resulting in a continuous spectrum of light appearing in the sky. The rainbow takes the form of a multicoloured circular arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the Sun. Rainbows can be caused by many forms of airborne water. These include not only rain, but also mist, spray, and airborne dew.

<span class="mw-page-title-main">Fog bow</span> Type of rainbow formed by fog droplets

A fog bow, sometimes called a white rainbow, is a similar phenomenon to a rainbow; however, as its name suggests, it appears as a bow in fog rather than rain. Because of the very small size of water droplets that cause fog—smaller than 0.05 millimeters (0.0020 in)—the fog bow has only very weak colors, with a red outer edge and bluish inner edge. The colors fade due to being smeared out by the diffraction effect of the smaller droplets.

<span class="mw-page-title-main">Circumhorizontal arc</span> Optical phenomenon

A circumhorizontal arc is an optical phenomenon that belongs to the family of ice halos formed by the refraction of sunlight or moonlight in plate-shaped ice crystals suspended in the atmosphere, typically in actual cirrus or cirrostratus clouds. In its full form, the arc has the appearance of a large, brightly spectrum-coloured band running parallel to the horizon, located far below the Sun or Moon. The distance between the arc and the Sun or Moon is twice as far as the common 22-degree halo. Often, when the halo-forming cloud is small or patchy, only fragments of the arc are seen. As with all halos, it can be caused by the Sun as well as the Moon.

<span class="mw-page-title-main">Circumzenithal arc</span> Optical phenomenon arising from refraction of sunlight through ice crystals

The circumzenithal arc, also called the circumzenith arc (CZA), the upside-down rainbow, and the Bravais arc, is an optical phenomenon similar in appearance to a rainbow, but belonging to the family of halos arising from refraction of sunlight through ice crystals, generally in cirrus or cirrostratus clouds, rather than from raindrops. The arc is located a considerable distance above the observed Sun and at most forms a quarter of a circle centered on the zenith. It has been called "a smile in the sky", its first impression being that of an upside-down rainbow. The CZA is one of the brightest and most colorful members of the halo family. Its colors, ranging from violet on top to red at the bottom, are purer than those of a rainbow because there is much less overlap in their formation.

<span class="mw-page-title-main">Cumberland Falls State Resort Park</span> Park in Kentucky, United States

Cumberland Falls State Resort Park is a park located just southwest of Corbin, Kentucky, and is contained entirely within the Daniel Boone National Forest. The park encompasses 1,657 acres (671 ha) and is named for its major feature, 68-foot-tall (21 m) Cumberland Falls. The falls are one of the few places in the western hemisphere where a moonbow can frequently be seen on nights with a full moon. The park is also the home of 44-foot (13 m) Eagle Falls. The section of the Cumberland River that includes the falls was designated a Kentucky Wild River by the Kentucky General Assembly through the Office of Kentucky Nature Preserves' Wild Rivers System. The forest in the park is also a dedicated State Nature Preserve.

<span class="mw-page-title-main">22° halo</span> Atmospheric optical phenomenon

A 22° halo is an atmospheric optical phenomenon that consists of a halo with an apparent radius of approximately 22° around the Sun or Moon. Around the Sun, it may also be called a sun halo. Around the Moon, it is also known as a moon ring, storm ring, or winter halo. It forms as sunlight or moonlight is refracted by millions of hexagonal ice crystals suspended in the atmosphere. Its radius, as viewed from Earth, is roughly the length of an outstretched hand at arm's length.

<span class="mw-page-title-main">Cloud iridescence</span> Optical phenomenon

Cloud iridescence or irisation is a colorful optical phenomenon that occurs in a cloud and appears in the general proximity of the Sun or Moon. The colors resemble those seen in soap bubbles and oil on a water surface. It is a type of photometeor. This fairly common phenomenon is most often observed in altocumulus, cirrocumulus, lenticular, and cirrus clouds. They sometimes appear as bands parallel to the edge of the clouds. Iridescence is also seen in the much rarer polar stratospheric clouds, also called nacreous clouds.

<span class="mw-page-title-main">Dewbow</span>

A dewbow is an optical effect, similar to a rainbow, where dewdrops instead of rain droplets reflect and disperse sunlight.

<span class="mw-page-title-main">Atmospheric optics</span> Study of the optical characteristics of the atmosphere or products of atmospheric processes

Atmospheric optics is "the study of the optical characteristics of the atmosphere or products of atmospheric processes .... [including] temporal and spatial resolutions beyond those discernible with the naked eye". Meteorological optics is "that part of atmospheric optics concerned with the study of patterns observable with the naked eye". Nevertheless, the two terms are sometimes used interchangeably.

<span class="mw-page-title-main">Earth's shadow</span> Shadow that Earth itself casts through its atmosphere and into outer space

Earth's shadow is the shadow that Earth itself casts through its atmosphere and into outer space, toward the antisolar point. During the twilight period, the shadow's visible fringe – sometimes called the dark segment or twilight wedge – appears as a dark and diffuse band just above the horizon, most distinct when the sky is clear.

<span class="mw-page-title-main">Optical phenomenon</span> Observable events that result from the interaction of light and matter

Optical phenomena are any observable events that result from the interaction of light and matter.

References

  1. 1 2 "Moonbow". Met Office. Retrieved 2023-06-14.
  2. Walklet, Keith S. (2006). "Lunar Rainbows – When to View and How to Photograph a "Moonbow"". The Ansel Adams Gallery. Archived from the original on 2007-06-24. Retrieved 2007-07-09.
  3. Miller, James (2018-05-28). "Examining the Phenomenon of Lunar Rainbows" . Retrieved 2023-06-14.
  4. Valerie Porter, “The Second Field Book of Country Queries” p. 89
  5. "Goat Island and Luna Island How Did they get The…". Niagara Falls Canada. Retrieved 17 December 2020.
  6. "'Moonbows,' Lunar Rainbows, Visible At Yosemite National Park (VIDEO)". Huffington Post—Green Blog. 15 July 2011. Retrieved 22 December 2012.
  7. Bailey, Bill (1995). "Cumberland Falls State Resort Park". Kentucky State Parks. Saginaw, Michigan: Glovebox Guidebooks of America. ISBN   978-1-881139-13-3.
  8. Manning, Russ (1999). The Historic Cumberland Plateau: An Explorer's Guide. Univ. of Tennessee Press. p. 106. ISBN   978-1-57233-044-3 . Retrieved 2011-10-28.
  9. "A Lunar Rainbow A Wonderful Sight Not To Be Missed...…". Victoria Falls Activities. Victoria Falls Travel Guide. Retrieved 22 December 2012.
  10. "Photographer captures moonbow over Waimea". Hawaii News Now. June 4, 2012. Retrieved 22 December 2012.