Optical phenomena refer to any observable events that occur due to the interaction of light and matter .
107-566: 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 . Rainbows can be full circles. However,
214-405: A cosmetic to redden cheeks and lips and also used henna to color their hair and paint their nails. The ancient Romans wore togas with red stripes on holidays, and the bride at a wedding wore a red shawl, called a flammeum . Red was used to color statues and the skin of gladiators. Red was also the color associated with army; Roman soldiers wore red tunics, and officers wore a cloak called
321-624: 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 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 . Optical phenomenon Many optical phenomena are closely tied to quantum mechanics . Common optical phenomena are often due to
428-549: A paludamentum which, depending upon the quality of the dye, could be crimson, scarlet or purple. In Roman mythology red is associated with the god of war, Mars . The vexilloid of the Roman Empire had a red background with the letters SPQR in gold . A Roman general receiving a triumph had his entire body painted red in honor of his achievement. The Romans liked bright colors, and many Roman villas were decorated with vivid red murals. The pigment used for many of
535-488: A battle meant that no prisoners would be taken. In 1793-94, red became the color of the French Revolution . A red Phrygian cap , or "liberty cap", was part of the uniform of the sans-culottes , the most militant faction of the revolutionaries. In the late 18th century, during a strike English dock workers carried red flags, and it thereafter became closely associated with the new labour movement, and later with
642-404: 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
749-476: A computer screen is made by a similar formula to that used by Cennino Cennini in the Renaissance to make violet, but using additive colors and light instead of pigment: it is created by combining red and blue light at equal intensity on a black screen. Violet is made on a computer screen in a similar way, but with a greater amount of blue light and less red light. As a ray of white sunlight travels through
856-434: A double rainbow, a second arc is seen outside the primary arc, and has 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
963-527: A fading stimulation of the L (long-wavelength) cone cells. Primates can distinguish the full range of the colors of the spectrum visible to humans, but many kinds of mammals, such as dogs and cattle, have dichromacy , which means they can see blues and yellows, but cannot distinguish red and green (both are seen as gray). Bulls, for instance, cannot see the red color of the cape of a bullfighter, but they are agitated by its movement. (See color vision ). One theory for why primates developed sensitivity to red
1070-414: 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
1177-470: A mystical light. Soon stained glass windows were being added to cathedrals all across France, England and Germany. In medieval painting red was used to attract attention to the most important figures; both Christ and the Virgin Mary were commonly painted wearing red mantles. In western countries red is a symbol of martyrs and sacrifice, particularly because of its association with blood. Beginning in
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#17327717268511284-404: 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
1391-405: 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
1498-407: 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
1605-479: 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
1712-488: 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
1819-458: 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
1926-403: A very visible symbol of his authority, and wore red shoes at his coronation. Kings, princes and, beginning in 1295, Roman Catholic cardinals began to wear red colored habitus . When Abbe Suger rebuilt Saint Denis Basilica outside Paris in the early 12th century, he added stained glass windows colored blue cobalt glass and red glass tinted with copper. Together they flooded the basilica with
2033-464: A wavelength between approximately 625 and 740 nanometers . It is a primary color in the RGB color model and the light just past this range is called infrared, or below red, and cannot be seen by human eyes, although it can be sensed as heat. In the language of optics, red is the color evoked by light that stimulates neither the S or the M (short and medium wavelength) cone cells of the retina, combined with
2140-410: 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
2247-455: 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
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#17327717268512354-695: Is banned in Denmark, Belgium, France and Switzerland, and was also banned in Sweden until the country joined the European Union in 1994. The European Union approves Allura Red AC as a food colorant, but EU countries' local laws banning food colorants are preserved. In the United States, Allura Red AC is approved by the Food and Drug Administration (FDA) for use in cosmetics , drugs , and food. It
2461-427: 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
2568-414: 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 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
2675-493: 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 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
2782-425: Is often visible. It appears about 10° outside of 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
2889-434: Is one of the three primary colors , along with blue and yellow. Painters in the Renaissance mixed red and blue to make violet: Cennino Cennini , in his 15th-century manual on painting, wrote, "If you want to make a lovely violet colour, take fine lac ( red lake ), ultramarine blue (the same amount of the one as of the other) with a binder"; he noted that it could also be made by mixing blue indigo and red hematite . In
2996-469: Is poor in low light, moonbows are often perceived to be white. It 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
3103-402: 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
3210-411: 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,
3317-491: Is that it allowed ripe fruit to be distinguished from unripe fruit and inedible vegetation. This may have driven further adaptations by species taking advantage of this new ability, such as the emergence of red faces. Red light is used to help adapt night vision in low-light or night time, as the rod cells in the human eye are not sensitive to red. In the RYB color model , which is the basis of traditional color theory , red
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3424-532: Is the color at the long wavelength end of the visible spectrum of light, next to orange and opposite violet . It has a dominant wavelength of approximately 625–740 nanometres . It is a primary color in the RGB color model and a secondary color (made from magenta and yellow ) in the CMYK color model , and is the complementary color of cyan . Reds range from the brilliant yellow-tinged scarlet and vermillion to bluish-red crimson , and vary in shade from
3531-709: Is the color most associated with courage. In western countries red is a symbol of martyrs and sacrifice, particularly because of its association with blood. Beginning in the Middle Ages, the Pope and Cardinals of the Roman Catholic Church wore red to symbolize the blood of Christ and the Christian martyrs. The banner of the Christian soldiers in the First Crusade was a red cross on a white field,
3638-478: Is the color symbolizing happiness and good fortune. Varieties of the color red may differ in hue , chroma (also called saturation, intensity, or colorfulness), or lightness (or value, tone, or brightness ), or in two or three of these qualities. Variations in value are also called tints and shades , a tint being a red or other hue mixed with white, a shade being mixed with black. Four examples are shown below. The human eye sees red when it looks at light with
3745-580: Is used in some tattoo inks and is used in many products, such as soft drinks , children's medications, and cotton candy . On June 30, 2010, the Center for Science in the Public Interest (CSPI) called for the FDA to ban Red 40. Because of public concerns about possible health risks associated with synthetic dyes, many companies have switched to using natural pigments such as carmine , made from crushing
3852-456: 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
3959-522: The Aztec people , the Paracas culture and other societies used cochineal , a vivid scarlet dye made from insects. From the 16th until the 19th century, cochineal became a highly profitable export from Spanish Mexico to Europe. In the 18th century, red began to take on a new identity as the color of resistance and revolution. It was already associated with blood, and with danger; a red flag hoisted before
4066-624: The Labour Party in the United Kingdom, founded in 1900. In Paris in 1832, a red flag was carried by working-class demonstrators in the failed June Rebellion , an event immortalised in Les Misérables ), and later in the 1848 French Revolution . The red flag was proposed as the new national French flag during the 1848 revolution, but was rejected by at the urging of the poet and statesman Alphonse Lamartine in favour of
4173-564: The Renaissance , the brilliant red costumes for the nobility and wealthy were dyed with kermes and cochineal . The 19th century brought the introduction of the first synthetic red dyes, which replaced the traditional dyes. Red became a symbolic color of communism and socialism ; Soviet Russia adopted a red flag following the Bolshevik Revolution in 1917. The Soviet red banner would subsequently be used throughout
4280-746: The St. George's Cross . According to Christian tradition, Saint George was a Roman soldier who was a member of the guards of the Emperor Diocletian , who refused to renounce his Christian faith and was martyred. The Saint George's Cross became the Flag of England in the 16th century, and now is part of the Union Flag of the United Kingdom, as well as the Flag of the Republic of Georgia . While red
4387-854: The particle or the wave nature of light. Some are quite subtle and observable only by precise measurement using scientific instruments. A famous example is the bending of starlight by the Sun during a solar eclipse, a phenomenon that serves as evidence for the curvature of space as predicted by the theory of relativity . Atmospheric optical phenomena include: Some phenomena are yet to be conclusively explained and may possibly be some form of optical phenomena. Some consider many of these "mysteries" to simply be local tourist attractions that are not worthy of thorough investigation. Ozerov, Ruslan P.; Vorobyev, Anatoli A. (2007). "Wave Optics and Quantum–Optical Phenomena". Physics for Chemists . pp. 361–422. doi : 10.1016/B978-044452830-8/50008-8 . ISBN 978-0-444-52830-8 . Red Red
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4494-535: The ruby laser in 1960. In 1962 the red helium–neon laser was invented, and these two types of lasers were widely used in many scientific applications including holography , and in education. Red helium–neon lasers were used commercially in LaserDisc players. The use of red laser diodes became widespread with the commercial success of modern DVD players, which use a 660 nm laser diode technology. Today, red and red-orange laser diodes are widely available to
4601-490: The CMY and CMYK color models, red is a secondary color subtractively mixed from magenta and yellow. In the RGB color model , red, green and blue are additive primary colors . Red, green and blue light combined makes white light, and these three colors, combined in different mixtures, can produce nearly any other color. This principle is used to generate colors on such as computer monitors and televisions. For example, magenta on
4708-437: The Middle Ages, the Pope and Cardinals of the Roman Catholic Church wore red to symbolize the blood of Christ and the Christian martyrs. The banner of the Christian soldiers in the First Crusade was a red cross on a white field, the St. George's Cross . According to Christian tradition, Saint George was a Roman soldier who was a member of the guards of the Emperor Diocletian , who refused to renounce his Christian faith and
4815-411: 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
4922-427: 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
5029-450: 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
5136-428: 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,
5243-409: The atmosphere to the eye is longest, the blue and green components are removed almost completely, leaving the longer wavelength orange and red light. The remaining reddened sunlight can also be scattered by cloud droplets and other relatively large particles, which give the sky above the horizon its red glow. Lasers emitting in the red region of the spectrum have been available since the invention of
5350-406: The atmosphere to the eye, some of the colors are scattered out of the beam by air molecules and airborne particles due to Rayleigh scattering , changing the final color of the beam that is seen. Colors with a shorter wavelength, such as blue and green, scatter more strongly, and are removed from the light that finally reaches the eye. At sunrise and sunset , when the path of the sunlight through
5457-413: 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
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#17327717268515564-426: The cells of the leaf, and this development is the result of complex interactions of many influences—both inside and outside the plant. Their formation depends on the breakdown of sugars in the presence of bright light as the level of phosphate in the leaf is reduced. During the summer growing season, phosphate is at a high level. It has a vital role in the breakdown of the sugars manufactured by chlorophyll. But in
5671-546: The coast of South Africa, paleoanthropologists in 2000 found evidence that, between 170,000 and 40,000 years ago, Late Stone Age people were scraping and grinding ochre , a clay colored red by iron oxide , probably with the intention of using it to color their bodies. Red hematite powder was also found scattered around the remains at a grave site in a Zhoukoudian cave complex near Beijing . The site has evidence of habitation as early as 700,000 years ago. The hematite might have been used to symbolize blood in an offering to
5778-498: The colors generated by a prism are often shown in classrooms. Optical phenomena encompass a broad range of events, including those caused by atmospheric optical properties, other natural occurrences, man-made effects, and interactions involving human vision (entoptic phenomena) . Also listed here are unexplained phenomena that could have an optical explanation and " optical illusions " for which optical explanations have been excluded. There are many phenomena that result from either
5885-480: 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 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
5992-471: 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 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
6099-647: The dead. Red, black and white were the first colors used by artists in the Upper Paleolithic age, probably because natural pigments such as red ochre and iron oxide were readily available where early people lived. Madder , a plant whose root could be made into a red dye, grew widely in Europe, Africa and Asia. The cave of Altamira in Spain has a painting of a bison colored with red ochre that dates to between 15,000 and 16,500 BC. A red dye called Kermes
6206-404: 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
6313-696: The effect is likely to be produced by perceived rather than actual performance. Judges of tae kwon do have been shown to favor competitors wearing red protective gear over blue, and, when asked, a significant majority of people say that red abstract shapes are more "dominant", "aggressive", and "likely to win a physical competition" than blue shapes. In contrast to its positive effect in physical competition and dominance behavior, exposure to red decreases performance in cognitive tasks and elicits aversion in psychological tests where subjects are placed in an "achievement" context (e.g. taking an IQ test ). Inside cave 13B at Pinnacle Point , an archeological site found on
6420-794: The entire history of the Soviet Union . China adopted its own red flag following the Chinese Communist Revolution . A red flag was also adopted by North Vietnam in 1954, and by all of Vietnam in 1975. Since red is the color of blood , it has historically been associated with sacrifice, danger, and courage. Modern surveys in Europe and the United States show red is also the color most commonly associated with heat, activity, passion, sexuality, anger, love, and joy. In China, India , and many other Asian countries it
6527-412: The fall, phosphate, along with the other chemicals and nutrients, moves out of the leaf into the stem of the plant. When this happens, the sugar-breakdown process changes, leading to the production of anthocyanin pigments. The brighter the light during this period, the greater the production of anthocyanins and the more brilliant the resulting color display. When the days of autumn are bright and cool, and
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#17327717268516634-434: 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 the internal reflection as 2 β , then
6741-411: 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 the rain, and
6848-443: 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
6955-453: The human population. It occurs more frequently (2–6%) in people of northern or western European ancestry, and less frequently in other populations. Red hair appears in people with two copies of a recessive gene on chromosome 16 which causes a mutation in the MC1R protein. Red hair varies from a deep burgundy through burnt orange to bright copper . It is characterized by high levels of
7062-504: The interaction of light from the Sun or Moon with the atmosphere, clouds, water, dust, and other particulates. A well-known example is the rainbow , which is created when sunlight is reflected and refracted through water droplets . Some phenomena, such as the green ray , are so rare they are sometimes thought to be mythical. Others, such as Fata Morganas , are commonplace in favored locations. Other phenomena are simply interesting aspects of optics , or optical effects. For instance,
7169-403: The iron components reflecting red light. Red meat gets its color from the iron found in the myoglobin and hemoglobin in the muscles and residual blood. Plants like apples , strawberries , cherries , tomatoes , peppers , and pomegranates are often colored by forms of carotenoids , red pigments that also assist photosynthesis . Red hair occurs naturally on approximately 1–2% of
7276-403: 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
7383-441: The laser's recordings to take up more space on the disc than would blue-laser recordings. The most common synthetic food coloring today is Allura Red AC , a red azo dye that goes by several names including: Allura Red , Food Red 17 , C.I. 16035 , FD&C Red 40 , It was originally manufactured from coal tar, but now is mostly made from petroleum. In Europe, Allura Red AC is not recommended for consumption by children. It
7490-495: 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 is present, however, but the human eye is not normally sensitive enough to see the colours. Long exposure photographs will sometimes show
7597-416: 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
7704-604: The miners were slaves or prisoners, and being sent to the cinnabar mines was a virtual death sentence. After the fall of the Western Roman Empire, red was adopted as a color of majesty and authority by the Byzantine Empire , and the princes of Europe. It also played an important part in the rituals of the Roman Catholic Church , symbolizing the blood of Christ and the Christian martyrs. In Western Europe, Emperor Charlemagne painted his palace red as
7811-403: 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
7918-466: The murals was called vermilion , and it came from the mineral cinnabar , a common ore of mercury . It was one of the finest reds of ancient times – the paintings have retained their brightness for more than twenty centuries. The source of cinnabar for the Romans was a group of mines near Almadén , southwest of Madrid , in Spain. Working in the mines was extremely dangerous, since mercury is highly toxic;
8025-411: 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, 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
8132-530: The nights are chilly but not freezing, the brightest colorations usually develop. Anthocyanins temporarily color the edges of some of the very young leaves as they unfold from the buds in early spring. They also give the familiar color to such common fruits as cranberries , red apples , blueberries , cherries , raspberries , and plums . Anthocyanins are present in about 10% of tree species in temperate regions, although in certain areas—a famous example being New England —up to 70% of tree species may produce
8239-573: 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
8346-411: The observer normally sees only an arc formed by illuminated droplets above 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
8453-401: 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
8560-428: 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
8667-408: 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
8774-463: The pale red pink to the dark red burgundy . Red pigment made from ochre was one of the first colors used in prehistoric art . The Ancient Egyptians and Mayans colored their faces red in ceremonies; Roman generals had their bodies colored red to celebrate victories. It was also an important color in China , where it was used to color early pottery and later the gates and walls of palaces. In
8881-461: The perception of dominance by others, leading to significant differences in mortality, reproductive success and parental investment between individuals displaying red and those not. In humans, wearing red has been linked with increased performance in competitions, including professional sport and multiplayer video games . Controlled tests have demonstrated that wearing red does not increase performance or levels of testosterone during exercise, so
8988-440: The pigment. In autumn forests they appear vivid in the maples , oaks , sourwood , sweetgums , dogwoods , tupelos , cherry trees and persimmons . These same pigments often combine with the carotenoids' colors to create the deeper orange, fiery reds, and bronzes typical of many hardwood species. (See Autumn leaf color ). Oxygenated blood is red due to the presence of oxygenated hemoglobin that contains iron molecules, with
9095-546: The public in the form of extremely inexpensive laser pointers . Portable, high-powered versions are also available for various applications. More recently, 671 nm diode-pumped solid state ( DPSS ) lasers have been introduced to the market for all-DPSS laser display systems, particle image velocimetry , Raman spectroscopy , and holography. Red's wavelength has been an important factor in laser technologies; red lasers, used in early compact disc technologies, are being replaced by blue lasers, as red's longer wavelength causes
9202-503: 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
9309-433: 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
9416-516: The reddish pigment pheomelanin (which also accounts for the red color of the lips) and relatively low levels of the dark pigment eumelanin . The term "redhead" (originally redd hede ) has been in use since at least 1510. Red is associated with dominance in a number of animal species. For example, in mandrills , red coloration of the face is greatest in alpha males, increasingly less prominent in lower ranking subordinates, and directly correlated with levels of testosterone . Red can also affect
9523-541: 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 the second-order or secondary rainbow. More internal reflections cause bows of higher orders—theoretically unto infinity. As more and more light
9630-409: 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
9737-529: 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 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
9844-410: 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
9951-437: 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
10058-416: 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
10165-528: The tiny female cochineal insect. This insect, originating in Mexico and Central America, was used to make the brilliant scarlet dyes of the European Renaissance. The red of autumn leaves is produced by pigments called anthocyanins . They are not present in the leaf throughout the growing season, but are actively produced towards the end of summer. They develop in late summer in the sap of
10272-467: The tricolor flag. It appeared again as the flag of the short-lived Paris Commune in 1871. It was then adopted by Karl Marx and the new European movements of socialism and communism . Soviet Russia adopted a red flag following the Bolshevik Revolution in 1917. The People's Republic of China adopted the red flag following the Chinese Communist Revolution . It was adopted by North Vietnam in 1954, and by all of Vietnam in 1975. Surveys show that red
10379-434: 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
10486-715: The upper classes. In Renaissance Flanders , people of all social classes wore red at celebrations. One such celebration was captured in The Wedding Dance (1566) by Pieter Bruegel the Elder . The painter Johannes Vermeer skilfully used different shades and tints of vermilion to paint the red skirt in The Girl with the Wine Glass , then glazed it with madder lake to make a more luminous color. In Latin America,
10593-588: 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
10700-528: 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
10807-483: 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
10914-415: The western sky during the morning and in 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
11021-496: Was later used by Romans, who imported it from Spain. A different variety of dye was made from Porphyrophora hamelii (Armenian cochineal) scale insects that lived on the roots and stems of certain herbs. It was mentioned in texts as early as the 8th century BC, and it was used by the ancient Assyrians and Persians. In ancient Egypt, red was associated with life, health, and victory. Egyptians would color themselves with red ochre during celebrations. Egyptian women used red ochre as
11128-531: Was made beginning in the Neolithic Period by drying and then crushing the bodies of the females of a tiny scale insect in the genus Kermes , primarily Kermes vermilio . The insects live on the sap of certain trees, especially Kermes oak trees near the Mediterranean region. Jars of kermes have been found in a Neolithic cave-burial at Adaoutse, Bouches-du-Rhône . Kermes from oak trees
11235-416: Was martyred. The Saint George's Cross became the Flag of England in the 16th century, and now is part of the Union Flag of the United Kingdom, as well as the Flag of the Republic of Georgia . In Renaissance painting, red was used to draw the attention of the viewer; it was often used as the color of the cloak or costume of Christ , the Virgin Mary , or another central figure. In Venice , Titian
11342-418: 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 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
11449-562: Was the master of fine reds, particularly vermilion ; he used many layers of pigment mixed with a semi-transparent glaze, which let the light pass through, to create a more luminous color. The figures of God, the Virgin Mary and two apostles are highlighted by their vermilion red costumes. Queen Elizabeth I of England liked to wear bright reds, before she adopted the more sober image of the "Virgin Queen". Red costumes were not limited to
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