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.
66-600: Arcobaleno means rainbow in Italian. Specifically it may refer to: Arcobaleno Records , a record label based in the UK and founded in 2005 by Serge Santiágo Arcobaleno (film) [ it ] , a 1943 Italian film Arcobaleno selvaggio , a 1984 Italian film Arcobaleno Valle d'Aosta , a coalition of political parties active in Italy's Aosta Valley Arcobaleno (Reborn) ,
132-411: A glory at the bow's centre. Fog bows should not be confused with ice halos , which are very common around the world and visible much more often than rainbows (of any order), yet are unrelated to rainbows. A sleetbow forms in the same way as a typical rainbow, with the exception that it occurs when light passes through falling sleet (ice pellets) instead of liquid water. As light passes through
198-404: A body of water before reaching the raindrops, if the water body is large, quiet over its entire surface, and close to the rain curtain. The reflection rainbow appears above the horizon. It intersects the normal rainbow at the horizon, and its arc reaches higher in the sky, with its centre as high above the horizon as the normal rainbow's centre is below it. Reflection bows are usually brightest when
264-502: 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 . Rainbows can be full circles. However, the observer normally sees only an arc formed by illuminated droplets above
330-602: A group of characters of the Reborn! anime and manga series Arcobaleno (tariff) , a public transport fare tariff used in the Swiss canton of Ticino Linea arcobaleno , a railway line that forms part of the Naples Metro Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title Arcobaleno . If an internal link led you here, you may wish to change
396-414: A liquid with no dispersion would be white, but brighter than a normal rainbow.) The light at the back of the raindrop does not undergo total internal reflection , and most of the light emerges from the back. However, light coming out the back of the raindrop does not create a rainbow between the observer and the Sun because spectra emitted from the back of the raindrop do not have a maximum of intensity, as
462-406: A partial rainbow, the circular rainbow can have a secondary bow or supernumerary bows as well. It is possible to produce the full circle when standing on the ground, for example by spraying a water mist from a garden hose while facing away from the sun. A circular rainbow should not be confused with the glory , which is much smaller in diameter and is created by different optical processes. In
528-405: A rainbow (2.36°). Further red of the first supplementary rainbow overlaps the violet of the primary rainbow, so rather than the final colour being a variant of spectral violet, it is actually a purple. The number of colour bands of a rainbow may therefore be different from the number of bands in a spectrum, especially if the droplets are particularly large or small. Therefore, the number of colours of
594-408: A rainbow is different from a spectrum, and the colours are less saturated. There is spectral smearing in a rainbow since, for any particular wavelength, there is a distribution of exit angles, rather than a single unvarying angle. In addition, a rainbow is a blurred version of the bow obtained from a point source, because the disk diameter of the sun (0.533°) cannot be neglected compared to the width of
660-479: A rainbow is variable. If, however, the word rainbow is used inaccurately to mean spectrum , it is the number of main colours in the spectrum. Moreover, rainbows have bands beyond red and violet in the respective near infrared and ultraviolet regions, however, these bands are not visible to humans. Only near frequencies of these regions to the visible spectrum are included in rainbows, since water and air become increasingly opaque to these frequencies, scattering
726-464: A rainbow, but unlike the latter, their origin lies in light refraction through hexagonal ice crystals rather than liquid water droplets. This means that they are not rainbows, but members of the large family of halos . Moonbow 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
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#1732780424758792-488: A series of overlapping frames. From above the Earth such as in an aeroplane, it is sometimes possible to see a rainbow as a full circle . This phenomenon can be confused with the glory phenomenon, but a glory is usually much smaller, covering only 5–20°. The sky inside a primary rainbow is brighter than the sky outside of the bow. This is because each raindrop is a sphere and it scatters light over an entire circular disc in
858-504: 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
924-461: A twinned rainbow. A numerical ray tracing study showed that a twinned rainbow on a photo could be explained by a mixture of 0.40 and 0.45 mm droplets. That small difference in droplet size resulted in a small difference in flattening of the droplet shape, and a large difference in flattening of the rainbow top. Meanwhile, the even rarer case of a rainbow split into three branches was observed and photographed in nature. In theory, every rainbow
990-410: Is a circle, but from the ground, usually only its upper half can be seen. Since the rainbow's centre is diametrically opposed to the Sun's position in the sky, more of the circle comes into view as the sun approaches the horizon, meaning that the largest section of the circle normally seen is about 50% during sunset or sunrise. Viewing the rainbow's lower half requires the presence of water droplets below
1056-455: Is a turning point – light hitting the outermost ring of the drop gets returned at less than 42°, as does the light hitting the drop nearer to its centre. There is a circular band of light that all gets returned right around 42°. If the Sun were a laser emitting parallel, monochromatic rays, then the luminance (brightness) of the bow would tend toward infinity at this angle if interference effects are ignored (see Caustic (optics) ) . But since
1122-428: Is differentiated in colour, creating a miniature rainbow. Supernumerary rainbows are clearest when raindrops are small and of uniform size. The very existence of supernumerary rainbows was historically a first indication of the wave nature of light, and the first explanation was provided by Thomas Young in 1804. When a rainbow appears above a body of water, two complementary mirror bows may be seen below and above
1188-400: Is difficult to photograph the complete semicircle of a rainbow in one frame, as this would require an angle of view of 84°. For a 35 mm camera, a wide-angle lens with a focal length of 19 mm or less would be required. Now that software for stitching several images into a panorama is available, images of the entire arc and even secondary arcs can be created fairly easily from
1254-451: Is present, however, but the human eye is not normally sensitive enough to see the colours. Long exposure photographs will sometimes show the colour in this type of rainbow. Fogbows form in the same way as rainbows, but they are formed by much smaller cloud and fog droplets that diffract light extensively. They are almost white with faint reds on the outside and blues inside; often one or more broad supernumerary bands can be discerned inside
1320-402: Is seen on the same side of the sky as the primary rainbow, about 10° outside it at an apparent angle of 50–53°. As a result of the "inside" of the secondary bow being "up" to the observer, the colours appear reversed compared to those of the primary bow. The secondary rainbow is fainter than the primary because more light escapes from two reflections compared to one and because the rainbow itself
1386-413: Is spread over a greater area of the sky. Each rainbow reflects white light inside its coloured bands, but that is "down" for the primary and "up" for the secondary. The dark area of unlit sky lying between the primary and secondary bows is called Alexander's band , after Alexander of Aphrodisias , who first described it. Unlike a double rainbow that consists of two separate and concentric rainbow arcs,
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#17327804247581452-411: Is their location in the direction of the sun (about 40° and 45° from the sun, respectively), causing them to become drowned in its glare. For these reasons, naturally occurring rainbows of an order higher than 2 are rarely visible to the naked eye. Nevertheless, sightings of the third-order bow in nature have been reported, and in 2011 it was photographed definitively for the first time. Shortly after,
1518-456: Is used when both the primary and secondary rainbows are visible. In theory, all rainbows are double rainbows, but since the secondary bow is always fainter than the primary, it may be too weak to spot in practice. Secondary rainbows are caused by a double reflection of sunlight inside the water droplets. Technically the secondary bow is centred on the sun itself, but since its angular size is more than 90° (about 127° for violet to 130° for red), it
1584-499: 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 Meteorology (circa 350 BC). Moonbows are most easily viewed when the Moon is at or nearest to its brightest phase full moon . For moonbows to have
1650-406: The second-order or secondary rainbow. More internal reflections cause bows of higher orders—theoretically unto infinity. As more and more light is lost with each internal reflection, however, each subsequent bow becomes progressively dimmer and therefore increasingly difficult to spot. An additional challenge in observing the third-order (or tertiary ) and fourth-order ( quaternary ) rainbows
1716-497: The (much more common) supernumerary bows and reflection rainbows. Like most atmospheric optical phenomena, rainbows can be caused by light from the Sun, but also from the Moon. In case of the latter, the rainbow is referred to as a lunar rainbow or moonbow . They are much dimmer and rarer than solar rainbows, requiring the Moon to be near-full in order for them to be seen. For the same reason, moonbows are often perceived as white and may be thought of as monochrome. The full spectrum
1782-470: The 19th-order rainbow, a pattern he called a "rose of rainbows". In the laboratory, it is possible to observe higher-order rainbows by using extremely bright and well collimated light produced by lasers . Up to the 200th-order rainbow was reported by Ng et al. in 1998 using a similar method but an argon ion laser beam. Tertiary and quaternary rainbows should not be confused with "triple" and "quadruple" rainbows—terms sometimes erroneously used to refer to
1848-407: 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
1914-411: The Sun's luminance is finite and its rays are not all parallel (it covers about half a degree of the sky) the luminance does not go to infinity. Furthermore, the amount by which light is refracted depends upon its wavelength , and hence its colour. This effect is called dispersion . Blue light (shorter wavelength) is refracted at a greater angle than red light, but due to the reflection of light rays from
1980-429: The Sun, lie on a cone pointing at the sun with the observer at the tip. The base of the cone forms a circle at an angle of 40–42° to the line between the observer's head and their shadow but 50% or more of the circle is below the horizon, unless the observer is sufficiently far above the earth's surface to see it all, for example in an aeroplane (see below). Alternatively, an observer with the right vantage point may see
2046-431: The arc. The light of the second arc is 90% polarised. 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, remembered by the mnemonic Richard Of York Gave Battle In Vain, or as the name of a fictional person ( Roy G. Biv ). The initialism is sometimes referred to in reverse order, as VIBGYOR. More modernly,
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2112-413: The back of the droplet, the blue light emerges from the droplet at a smaller angle to the original incident white light ray than the red light. Due to this angle, blue is seen on the inside of the arc of the primary rainbow, and red on the outside. The result of this is not only to give different colours to different parts of the rainbow, but also to diminish the brightness. (A "rainbow" formed by droplets of
2178-563: 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 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
2244-404: The earlier equation for φ yields 2 φ max ≈ 42° as the radius angle of the rainbow. For red light (wavelength 750nm, n = 1.330 based on the dispersion relation of water ), the radius angle is 42.5°; for blue light (wavelength 350nm, n = 1.343 ), the radius angle is 40.6°. A secondary rainbow, at a greater angle than the primary rainbow, is often visible. The term double rainbow
2310-423: The eastern sky during the early evening. The most spectacular rainbow displays happen when half the sky is still dark with raining clouds and the observer is at a spot with clear sky in the direction of the Sun. The result is a luminous rainbow that contrasts with the darkened background. During such good visibility conditions, the larger but fainter secondary rainbow is often visible. It appears about 10° outside of
2376-418: The fourth-order rainbow was photographed as well, and in 2014 the first ever pictures of the fifth-order (or quinary ) rainbow were published. The quinary rainbow lies partially in the gap between the primary and secondary rainbows and is far fainter than even the secondary. In a laboratory setting, it is possible to create bows of much higher orders. Felix Billet (1808–1882) depicted angular positions up to
2442-400: The full circle in a fountain or waterfall spray. Conversely, at lower latitudes near midday (specifically, when the sun's elevation exceeds 42 degrees) a rainbow will not be visible against the sky. It is possible to determine the perceived angle which the rainbow subtends as follows. Given a spherical raindrop, and defining the perceived angle of the rainbow as 2 φ , and the angle of
2508-493: 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
2574-408: The ground, and centered on a line from the Sun to the observer's eye. In a primary rainbow, the arc shows red on the outer part and violet on the inner side. This rainbow is caused by light being refracted when entering a droplet of water, then reflected inside on the back of the droplet and refracted again when leaving it. In a double rainbow, a second arc is seen outside the primary arc, and has
2640-399: The horizon (1, 2) with their reflected counterparts below it (3, 4), and the reflection primary and secondary bows above the horizon (5, 6) with their reflected counterparts below it (7, 8). Occasionally a shower may happen at sunrise or sunset, where the shorter wavelengths like blue and green have been scattered and essentially removed from the spectrum. Further scattering may occur due to
2706-444: The horizon, originating from different light paths. Their names are slightly different. A reflected rainbow may appear in the water surface below the horizon. The sunlight is first deflected by the raindrops, and then reflected off the body of water, before reaching the observer. The reflected rainbow is frequently visible, at least partially, even in small puddles. A reflection rainbow may be produced where sunlight reflects off
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2772-404: The inner edge. The colours are dim because the bow in each colour is very broad and the colours overlap. Fogbows are commonly seen over water when air in contact with the cooler water is chilled, but they can be found anywhere if the fog is thin enough for the sun to shine through and the sun is fairly bright. They are very large—almost as big as a rainbow and much broader. They sometimes appear with
2838-490: The internal reflection as 2 β , then the angle of incidence of the Sun's rays with respect to the drop's surface normal is 2 β − φ . Since the angle of refraction is β , Snell's law gives us where n = 1.333 is the refractive index of water. Solving for φ , we get The rainbow will occur where the angle φ is maximum with respect to the angle β . Therefore, from calculus , we can set dφ / dβ = 0 , and solve for β , which yields Substituting back into
2904-404: The language that one uses, with people whose language has fewer colour words seeing fewer discrete colour bands. When sunlight encounters a raindrop, part of the light is reflected and the rest enters the raindrop. The light is refracted at the surface of the raindrop. When this light hits the back of the raindrop, some of it is reflected off the back. When the internally reflected light reaches
2970-419: The light. The UV band is sometimes visible to cameras using black and white film. The question of whether everyone sees seven colours in a rainbow is related to the idea of linguistic relativity . Suggestions have been made that there is universality in the way that a rainbow is perceived. However, more recent research suggests that the number of distinct colours observed and what these are called depend on
3036-504: The link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Arcobaleno&oldid=1178446774 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Rainbow A rainbow is an optical phenomenon caused by refraction , internal reflection and dispersion of light in water droplets resulting in
3102-568: 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. 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 , Yosemite National Park , California and Cumberland Falls , near Corbin , Kentucky . Victoria Falls , on
3168-405: The most intense light at 42°. This angle is independent of the size of the drop, but does depend on its refractive index . Seawater has a higher refractive index than rain water, so the radius of a "rainbow" in sea spray is smaller than that of a true rainbow. This is visible to the naked eye by a misalignment of these bows. The reason the returning light is most intense at about 42° is that this
3234-581: The number of notes in a musical scale. Newton chose to divide the visible spectrum into seven colours out of a belief derived from the beliefs of the ancient Greek sophists , 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. 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 . The colour pattern of
3300-401: The observer's eye. This light is what constitutes the rainbow for that observer. The whole system composed by the Sun's rays, the observer's head, and the (spherical) water drops has an axial symmetry around the axis through the observer's head and parallel to the Sun's rays. The rainbow is curved because the set of all the raindrops that have the right angle between the observer, the drop, and
3366-430: The observer's horizon, as well as sunlight that is able to reach them. These requirements are not usually met when the viewer is at ground level, either because droplets are absent in the required position, or because the sunlight is obstructed by the landscape behind the observer. From a high viewpoint such as a high building or an aircraft, however, the requirements can be met and the full-circle rainbow can be seen. Like
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#17327804247583432-404: The order of its colours reversed, with red on the inner side of the arc. This is caused by the light being reflected twice on the inside of the droplet before leaving it. Rainbows can be observed whenever there are water drops in the air and sunlight shining from behind the observer at a low altitude angle . Because of this, rainbows are usually seen in the western sky during the morning and in
3498-409: The other visible rainbows do, and thus the colours blend together rather than forming a rainbow. A rainbow does not exist at one particular location. Many rainbows exist; however, only one can be seen depending on the particular observer's viewpoint as droplets of light illuminated by the sun. All raindrops refract and reflect the sunlight in the same way, but only the light from some raindrops reaches
3564-445: The primary rainbow, with inverse order of colours. The rainbow effect is also commonly seen near waterfalls or fountains. In addition, the effect can be artificially created by dispersing water droplets into the air during a sunny day. Rarely, a moonbow , lunar rainbow or nighttime rainbow, can be seen on strongly moonlit nights. As human visual perception for colour is poor in low light, moonbows are often perceived to be white. It
3630-407: The rain, and the result can be the rare and dramatic monochrome or red rainbow. In addition to the common primary and secondary rainbows, it is also possible for rainbows of higher orders to form. The order of a rainbow is determined by the number of light reflections inside the water droplets that create it: One reflection results in the first-order or primary rainbow; two reflections create
3696-505: The rainbow is often divided into red, orange, yellow, green, cyan, blue and violet. 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, 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
3762-433: The raindrops. Some rays are in phase , reinforcing each other through constructive interference , creating a bright band; others are out of phase by up to half a wavelength, cancelling each other out through destructive interference , and creating a gap. Given the different angles of refraction for rays of different colours, the patterns of interference are slightly different for rays of different colours, so each bright band
3828-409: The right circumstances, a glory and a (circular) rainbow or fog bow can occur together. Another atmospheric phenomenon that may be mistaken for a "circular rainbow" is the 22° halo , which is caused by ice crystals rather than liquid water droplets, and is located around the Sun (or Moon), not opposite it. In certain circumstances, one or several narrow, faintly coloured bands can be seen bordering
3894-411: The sky. The radius of the disc depends on the wavelength of light, with red light being scattered over a larger angle than blue light. Over most of the disc, scattered light at all wavelengths overlaps, resulting in white light which brightens the sky. At the edge, the wavelength dependence of the scattering gives rise to the rainbow. The light of a primary rainbow arc is 96% polarised tangential to
3960-608: The sleet, the light is refracted causing the rare phenomena. These have been documented across United States with the earliest publicly documented and photographed sleetbow being seen in Richmond, Virginia on 21 December 2012. Just like regular rainbows, these can also come in various forms, with a monochrome sleetbow being documented on 7 January 2016 in Valparaiso, Indiana. The circumzenithal and circumhorizontal arcs are two related optical phenomena similar in appearance to
4026-437: The sun is low because at that time its light is most strongly reflected from water surfaces. As the sun gets lower the normal and reflection bows are drawn closer together. Due to the combination of requirements, a reflection rainbow is rarely visible. Up to eight separate bows may be distinguished if the reflected and reflection rainbows happen to occur simultaneously: the normal (non-reflection) primary and secondary bows above
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#17327804247584092-416: The surface again, once more some is internally reflected and some is refracted as it exits the drop. (The light that reflects off the drop, exits from the back, or continues to bounce around inside the drop after the second encounter with the surface, is not relevant to the formation of the primary rainbow.) The overall effect is that part of the incoming light is reflected back over the range of 0° to 42°, with
4158-434: The twinned rainbow shows the same spectrum as a regular rainbow. The cause of a twinned rainbow is believed to be the combination of different sizes of water drops falling from the sky. Due to air resistance, raindrops flatten as they fall, and flattening is more prominent in larger water drops. When two rain showers with different-sized raindrops combine, they each produce slightly different rainbows which may combine and form
4224-591: The usual spectrum pattern. The effect becomes apparent when water droplets are involved that have a diameter of about 1 mm or less; the smaller the droplets are, the broader the supernumerary bands become, and the less saturated their colours. Due to their origin in small droplets, supernumerary bands tend to be particularly prominent in fogbows . Supernumerary rainbows cannot be explained using classical geometric optics . The alternating faint bands are caused by interference between rays of light following slightly different paths with slightly varying lengths within
4290-529: The very rare twinned rainbow appears as two rainbow arcs that split from a single base. The colours in the second bow, rather than reversing as in a secondary rainbow, appear in the same order as the primary rainbow. A "normal" secondary rainbow may be present as well. Twinned rainbows can look similar to, but should not be confused with supernumerary bands . The two phenomena may be told apart by their difference in colour profile: supernumerary bands consist of subdued pastel hues (mainly pink, purple and green), while
4356-483: The violet edge of a rainbow; i.e., inside the primary bow or, much more rarely, outside the secondary. These extra bands are called supernumerary rainbows or supernumerary bands ; together with the rainbow itself the phenomenon is also known as a stacker rainbow . The supernumerary bows are slightly detached from the main bow, become successively fainter along with their distance from it, and have pastel colours (consisting mainly of pink, purple and green hues) rather than
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