Rainbow From Wikipedia, the free encyclopedia For other uses, see Rainbow (disambiguation).

Double rainbow and supernumerary rainbows on the inside of the primary arc. The shadow of the photographer's head on the bottom marks the centre of the rainbow circle (antisolar point). A rainbow is an optical and meteorological phenomenon that causes a spectrum of light to appear in the sky when the Sun shines on to droplets of moisture in the Earth's atmosphere. It takes the form of a multicoloured arc. Rainbows caused by sunlight always appear in the section of sky directly opposite the sun. In a so-called "primary rainbow" (the lowest, and also normally the brightest rainbow) the arc of a rainbow shows red on the outer (or upper) part of the arc, and violet on the inner section. This rainbow is caused by light being refracted then reflected once in droplets of water. In a double rainbow, a second arc may be seen above and outside the primary arc, and has the order of its colours reversed (red faces inward toward the other rainbow, in both rainbows). This second rainbow is caused by light reflecting twice inside water droplets. The region between a double rainbow is dark, and is known as "Alexander's band" or "Alexander's dark band". The reason for this dark band is that, while light below the primary rainbow comes from droplet reflection, and light above the upper (secondary) rainbow also comes from droplet reflection, there is no mechanism for the region between a double rainbow to show any light reflected from water drops. It is impossible for an observer to maneuver to see any rainbow from water droplets at any angle other than the customary one (which is 42 degrees from the direction opposite the Sun). Even if an observer sees another observer who seems "under" or "at the end" of a rainbow, the second observer will see a different rainbow further off-yet, at the same angle as seen by the first observer. Thus, a "rainbow" is not a physical object, and cannot be physically approached. A rainbow spans a continuous spectrum of colours; the distinct bands (including the number of bands) are an artefact of human colour vision, and no banding of any type is seen in a black-and- white photo of a rainbow (only a smooth gradation of intensity to a maximum, then fading to a minimum at the other side of the arc). For colours seen by a normal human eye, the most commonly cited and remembered sequence, in English, is Newton's sevenfold red, orange, yellow, green, blue, indigo and violet (popularly memorized by mnemonics like Roy G. Biv). However, colour-blind persons will see fewer colours. Rainbows can be caused by many forms of airborne water. These include not only rain, but also mist, spray, and airborne dew. Rainbows may also form in mist, such as that of a waterfall

Rainbow with a faint reflected rainbow in the lake Contents [hide] • 1 Visibility • 2 Spectrum • 3 Explanation • 4 Variations o 4.1 Double rainbow o 4.2 Supernumerary rainbow o 4.3 Reflected rainbow, reflection rainbow o 4.4 Monochrome rainbow o 4.5 Circumhorizontal arc o 4.6 Rainbows on Titan • 5 Scientific history • 6 Culture o 6.1 Religious Belief o 6.2 Art o 6.3 Literature o 6.4 Music o 6.5 Films o 6.6 Flags • 7 See also • 8 Notes • 9 References • 10 External links [edit] Visibility Rainbows may also form in the spray created by waves (called spray bows)

Rainbow after sunlight bursts through after an intense shower in Maraetai, New Zealand. Rainbows can be observed whenever there are water drops in the air and sunlight shining from behind at a low altitude angle. 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. 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.[1] 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 lens with a focal length of 19 mm or less wide-angle lens would be required. Now that powerful 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 a series of overlapping frames. From an aeroplane, one has the opportunity to see the whole circle of the rainbow, with the plane's shadow in the centre. This phenomenon can be confused with the glory, but a glory is usually much smaller, covering only 5–20°. At good visibility conditions (for example, a dark cloud behind the rainbow), the second arc can be seen, with inverse order of colours. At the background of the blue sky, the second arc is barely visible. [edit] Spectrum A rainbow spans a continuous spectrum of colours—there are no "bands." The apparent discreteness is an artefact of the photopigments in the human eye and of the neural processing of our photoreceptor outputs in the brain. Because the peak response of human colour receptors varies from person to person, different individuals will see slightly different colours, and persons with colour blindness will see a smaller set of colours. However, the seven colours listed below are thought to be representative of how humans everywhere,[2] with normal colour vision, see the rainbow. The final colour in the rainbow is violet, not purple. Newton originally (1672) named only five primary colours: red, yellow, green, blue and violet. Later he included orange and indigo, giving seven colours by analogy to the number of notes in a musical scale.[3]

Red Orange Yellow Green Blue Indigo Violet

A corresponding article in the Japanese Wikipedia may contain information and sources useful in building this article. (May 2011) Click [show] on the right for instructions.[show] [edit] Explanation This article may need to be rewritten entirely to comply with Wikipedia's quality standards. You can help. The discussion page may contain suggestions. (June 2011)

The light is first refracted entering the surface of the raindrop, reflected off the back of the drop, and again refracted as it leaves the drop. The overall effect is that the incoming light is reflected back over a wide range of angles, with the most intense light at an angle of 40–42°. The 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 a true rainbow. This is visible to the naked eye by a misalignment of these bows.[4] 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 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. Contrary to popular belief, the light at the back of the raindrop does not undergo total internal reflection, and some light does emerge 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 the other visible rainbows do, and thus the colours blend together rather than forming a rainbow.[5] Light rays enter a raindrop from one direction (typically a straight line from the Sun), reflect off White light separates into different colours the back of the raindrop, and fan out as they leave on entering the raindrop due to dispersion, the raindrop. The light leaving the rainbow is causing red light to be refracted less than spread over a wide angle, with a maximum intensity blue light. at 40.89–42°.

A rainbow does not actually exist at a particular location in the sky. Its apparent position depends on the observer's location and the position of the Sun. All raindrops refract and reflect the sunlight in the same way, but only the light from some raindrops reaches the observer's eye. This light is what constitutes the rainbow for that observer. The position of a rainbow in the sky is always in the opposite direction of the Sun with respect to the observer, and the interior is always slightly brighter than the exterior. The bow is centred on the shadow of the observer's head, or more exactly at the antisolar point (which is below the horizon during the daytime), appearing at an angle of 40–42° to the line between the observer's head and its shadow. As a result, if the Sun is higher than 42°, then the rainbow is below the horizon and usually cannot be seen as there are not usually sufficient raindrops between the horizon (that is: eye height) and the ground, to contribute. Exceptions occur when the observer is high above the ground, for example in an aeroplane (see above), on top of a mountain, or above a waterfall. [edit] Variations [edit] Double rainbow "Double rainbow" redirects here. For other uses, see Double Rainbow (disambiguation).

Some light reflects twice inside the raindrop A double rainbow features reversed colours in before exiting to the viewer. When the incident the outer (secondary) bow, with the dark light is very bright, this can be seen as a secondary Alexander's band between the bows. rainbow, brightest at 50–53°.

Although most people will not notice it because they are not actively looking for it, a dim secondary rainbow is often present outside the primary bow. Secondary rainbows are caused by a double reflection of sunlight inside the raindrops, and appear at an angle of 50–53°. As a result of the second reflection, the colours of a secondary rainbow are inverted compared to the primary bow, with blue on the outside and red on the inside. The secondary rainbow is fainter than the primary because more light escapes from two reflections compared to one and because the rainbow itself is spread over a greater area of the sky. 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. A very dim tertiary rainbow, caused by a triple reflection of sunlight inside the raindrops, has been seen on rare occasions.[6] This bow appears on the same side of the sky as the Sun, making it hard to spot. It has a radius of about 41° and the outer colour is red. Higher-order rainbows were described by Felix Billet (1808–1882) who depicted angular positions up to the 19th-order rainbow, a pattern he called a "rose of rainbows".[7][8] 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.[9] [edit] Supernumerary rainbow

A contrast-enhanced photograph of a supernumerary rainbow, with additional green and violet arcs inside the primary bow. A supernumerary rainbow—also known as a stacker rainbow—is an infrequent phenomenon, consisting of several faint rainbows on the inner side of the primary rainbow, and very rarely also outside the secondary rainbow. Supernumerary rainbows are slightly detached and have pastel colour bands that do not fit the usual pattern. It is not possible to explain their existence using classical geometric optics. The alternating faint rainbows are caused by interference between rays of light following slightly different paths with slightly varying lengths within 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, canceling 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 is differentiated in colour, creating a miniature rainbow. Supernumerary rainbows are clearest when raindrops are small and of similar 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. [edit] Reflected rainbow, reflection rainbow Reflection rainbow and normal rainbow, at sunset When a rainbow appears above a body of water, two complementary mirror bows may be seen below and above the horizon, originating from different light paths. Their names are slightly different. A reflected rainbow will appear as a mirror image in the water surface below the horizon, if the surface is quiet (see photo above). 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. Where sunlight reflects off a body of water before reaching the raindrops (see diagram), it may produce a reflection rainbow (see photo at the right), 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. Due to the combination of requirements, a reflection rainbow is rarely visible. Six (or even eight) bows may be distinguished if the reflection of the reflection bow, and the secondary bow with its reflections happen to appear simultaneously.[10] [edit] Monochrome rainbow

An unenhanced photo of a red (monochrome) rainbow. 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 the result can be the rare and dramatic monochrome rainbow. Rainbows under moonlight (Moonbows) are often perceived as white and may be thought of as monochrome. Technically, the full spectrum is present but our eyes are not normally sensitive enough to see the colours. Long exposure photographs will sometimes show the colour in this type of rainbow. [edit] Circumhorizontal arc The circumhorizontal arc is sometimes referred to by the misnomer "fire rainbow". As it originates in ice crystals, it is not a rainbow but a halo.[11] [edit] Rainbows on Titan It has been suggested that rainbows might exist on Saturn's moon Titan, as it has a wet surface and humid clouds. The radius of a Titan rainbow would be about 49° instead of 42°, because the fluid in that cold environment is methane instead of water. A visitor might need infrared goggles to see the rainbow, as Titan's atmosphere is more transparent for those wavelengths.[12] [edit] Scientific history The classical Greek scholar Aristotle (384–322 BCE) was first to devote serious attention to the rainbow. According to Raymond L. Lee and Alistair B. Fraser, "Despite its many flaws and its appeal to Pythagorean numerology, Aristotle's qualitative explanation showed an inventiveness and relative consistency that was unmatched for centuries. After Aristotle's death, much rainbow theory consisted of reaction to his work, although not all of this was uncritical."[13] In the Naturales Quaestiones (ca. 65 AD), Seneca devotes a whole book to rainbows, heaping up a number of observations and hypotheses. He notices that rainbows appear always opposite to the sun, that they appear in water sprayed by a rower or even in the water spat by a launderer on dresses; he even speaks of rainbows produced by small rods (virgulae) of glass, anticipating Newton's experiences with prisms. He takes into account two theories: one, that the rainbow is produced by the sun reflecting in each water-drop, the other, that it is produced by the sun reflected in a cloud shaped like a concave mirror. He favors the latter theory. He observes other phenomena related with rainbows: the mysterious "virgae" (rods) and the parhelia. The Persian physicist and polymath, Ibn al-Haytham (Alhazen; 965–1039), attempted to provide a scientific explanation for the rainbow phenomenon. In his Maqala fi al-Hala wa Qaws Quzah (On the Rainbow and Halo), he "explained the formation of rainbow as an image, which forms at a concave mirror. If the rays of light coming from a farther light source reflect to any point on axis of the concave mirror, they form concentric circles in that point. When it is supposed that the sun as a farther light source, the eye of viewer as a point on the axis of mirror and a cloud as a reflecting surface, then it can be observed the concentric circles are forming on the axis."[14] He was not able to verify this because his theory that "light from the sun is reflected by a cloud before reaching the eye" did not allow for a possible experimental verification.[15] This explanation was later repeated by Averroes,[14] and, though incorrect, provided the groundwork for the correct explanations later given by Kamāl al-Dīn al-Fārisī (1267–ca. 1319/1320) and Theodoric of Freiberg (c.1250–1310).[16] Ibn al-Haytham supported the Aristotelian views that the rainbow is caused by reflection alone and that its colours are not real like object colours.[17] Ibn al-Haytham's contemporary, the Persian philosopher and polymath Ibn Sīnā (Avicenna; 980– 1037), provided an alternative explanation, writing "that the bow is not formed in the dark cloud but rather in the very thin mist lying between the cloud and the sun or observer. The cloud, he thought, serves simply as the background of this thin substance, much as a quicksilver lining is placed upon the rear surface of the glass in a mirror. Ibn Sīnā would change the place not only of the bow, but also of the colour formation, holding the iridescence to be merely a subjective sensation in the eye."[18] This explanation, however, was also incorrect.[14] Ibn Sīnā's account accepts many of Aristotle's arguments on the rainbow.[17] In Song Dynasty China (960–1279), a polymathic scholar-official named Shen Kuo (1031–1095) hypothesized—as a certain Sun Sikong (1015–1076) did before him—that rainbows were formed by a phenomenon of sunlight encountering droplets of rain in the air.[19] Paul Dong writes that Shen's explanation of the rainbow as a phenomenon of atmospheric refraction "is basically in accord with modern scientific principles."[20] The Persian astronomer, Qutb al-Din al-Shirazi (1236–1311), gave a fairly accurate explanation for the rainbow phenomenon. This was elaborated on by his student, Kamāl al-Dīn al-Fārisī (1260–1320), who gave a more mathematically satisfactory explanation of the rainbow. He "proposed a model where the ray of light from the sun was refracted twice by a water droplet, one or more reflections occurring between the two refractions." He verified this through extensive experimentation using a transparent sphere filled with water and a camera obscura.[15] [unreliable source?] As he noted in his Kitab Tanqih al-Manazir (The Revision of the Optics), al-Farisi used a large clear vessel of glass in the shape of a sphere, which was filled with water, in order to have an experimental large-scale model of a rain drop. He then placed this model within a camera obscura that has a controlled aperture for the introduction of light. He projected light unto the sphere and ultimately deduced through several trials and detailed observations of reflections and refractions of light that the colours of the rainbow are phenomena of the decomposition of light. His research had resonances with the studies of his contemporary Theodoric of Freiberg (without any contacts between them; even though they both relied on Aristotle's and Ibn al-Haytham's legacy), and later with the experiments of Descartes and Newton in dioptrics (for instance, Newton conducted a similar experiment at Trinity College, though using a prism rather than a sphere).[21][22][23][24][verification needed] In Europe, Ibn al-Haytham's Book of Optics was translated into Latin and studied by Robert Grosseteste. His work on light was continued by Roger Bacon, who wrote in his Opus Majus of 1268 about experiments with light shining through crystals and water droplets showing the colours of the rainbow.[25] In addition, Bacon was the first to calculate the angular size of the rainbow. He stated that the rainbow summit can not appear higher than 42° above the horizon.[26] Theodoric of Freiberg is known to have given an accurate theoretical explanation of both the primary and secondary rainbows in 1307. He explained the primary rainbow, noting that "when sunlight falls on individual drops of moisture, the rays undergo two refractions (upon ingress and egress) and one reflection (at the back of the drop) before transmission into the eye of the observer".[27] He explained the secondary rainbow through a similar analysis involving two refractions and two reflections. René Descartes' sketch of how primary and secondary rainbows are formed Descartes' 1637 treatise, Discourse on Method, further advanced this explanation. Knowing that the size of raindrops did not appear to affect the observed rainbow, he experimented with passing rays of light through a large glass sphere filled with water. By measuring the angles that the rays emerged, he concluded that the primary bow was caused by a single internal reflection inside the raindrop and that a secondary bow could be caused by two internal reflections. He supported this conclusion with a derivation of the law of refraction (subsequently to, but independently of, Snell) and correctly calculated the angles for both bows. His explanation of the colours, however, was based on a mechanical version of the traditional theory that colours were produced by a modification of white light.[28][29] Isaac Newton demonstrated that white light was composed of the light of all the colours of the rainbow, which a glass prism could separate into the full spectrum of colours, rejecting the theory that the colours were produced by a modification of white light. He also showed that red light is refracted less than blue light, which led to the first scientific explanation of the major features of the rainbow.[30] Newton's corpuscular theory of light was unable to explain supernumerary rainbows, and a satisfactory explanation was not found until Thomas Young realised that light behaves as a wave under certain conditions, and can interfere with itself. Young's work was refined in the 1820s by George Biddell Airy, who explained the dependence of the strength of the colours of the rainbow on the size of the water droplets. Modern physical descriptions of the rainbow are based on Mie scattering, work published by Gustav Mie in 1908. Advances in computational methods and optical theory continue to lead to a fuller understanding of rainbows. For example, Nussenzveig provides a modern overview.[31] [edit] Culture [edit] Religious Belief

The "end" of a rainbow. An observer located at this point would not see this rainbow. Main article: Rainbows in mythology The rainbow has a place in legend owing to its beauty and the historical difficulty in explaining the phenomenon. In Greco-Roman mythology, the rainbow was considered to be a path made by a messenger (Iris) between Earth and Heaven. In Chinese mythology, the rainbow was a slit in the sky sealed by goddess Nüwa using stones of five different colours. In Hindu religion, the rainbow is called Indradhanush, meaning "the bow (Sanskrit and Hindi: dhanush is bow) of Indra, the god of lightning, thunder and rain". Another Indian mythology says the rainbow is the bow of Rama, the incarnation of Vishnu. It is called Rangdhonu in Bengali, dhonu (dhanush) meaning bow. Likewise, in mythology of Arabian Peninsula, the rainbow, called Qaus Quzaħ in Arabic, is the war bow of the god Quzaħ. In Armenian mythology rainbow - is a belt of Tir, which was originally a god Sun, and then - god of knowledge. Eating options are apricot's belt, Belt of Our Lady or the Arch of God. In Norse Mythology, a rainbow called the Bifröst Bridge connects the realms of Ásgard and Midgard, homes of the gods and humans, respectively. The Irish leprechaun's secret hiding place for his pot of gold is usually said to be at the end of the rainbow. This place is impossible to reach, because the rainbow is an optical effect which depends on the location of the viewer. When walking towards the end of a rainbow, it will appear to "move" further away (two people who simultaneously observe a rainbow at different locations will disagree about where a rainbow is). Another ancient portrayal of the rainbow is given in the Epic of Gilgamesh: the rainbow is the "jewelled necklace of the Great Mother Ishtar" that she lifts into the sky as a promise that she "will never forget these days of the great flood" that destroyed her children. (The Epic of Gilgamesh, Tablet Eleven) Then Ishtar arrived. She lifted up the necklace of great jewels that her father, Anu, had created to please her and said, "Heavenly gods, as surely as this jewelled necklace hangs upon my neck, I will never forget these days of the great flood. Let all of the gods except Enlil come to the offering. Enlil may not come, for without reason he brought forth the flood that destroyed my people." According to Christian religion and Judaic religion, after Noah's flood God put the rainbow in the sky as the sign of His promise that He would never again destroy the earth with flood (Genesis 9:13–17):[32] I do set my bow in the cloud, and it shall be for a token of a covenant between me and the earth. And it shall come to pass, when I bring a cloud over the earth, that the bow shall be seen in the cloud: And I will remember my covenant, which is between me and you and every living creature of all flesh; and the waters shall no more become a flood to destroy all flesh. And the bow shall be in the cloud; and I will look upon it, that I may remember the everlasting covenant between God and every living creature of all flesh that is upon the earth. And God said unto Noah, This is the token of the covenant, which I have established between me and all flesh that is upon the earth. The Church of Jesus Christ of Latter-Day Saints founder and prophet Joseph Smith stated that the second coming of the Christ would not occur in any year in which a rainbow is seen. "The Lord deals with this people as a tender parent with a child, communicating light and intelligence and the knowledge of his ways as they can bear it. The inhabitants of the earth are asleep; they know not the day of their visitation. The Lord hath set the bow in the cloud for a sign that while it shall be seen, seed time and harvest, summer and winter shall not fail; but when it shall disappear woe to that generation, for behold the end cometh quickly." Teachings of the Prophet Joseph Smith, Section Six 1843-44, p.305 "I have asked of the Lord concerning His coming; and while asking the Lord, He gave a sign and said, "In the days of Noah I set a bow in the heavens as a sign and token that in any year that the bow should be seen the Lord would not come; but there should be seed time and harvest during that year: but whenever you see the bow withdrawn, it shall be a token that there shall be famine, pestilence, and great distress among the nations, and that the coming of the Messiah is not far distant." Teachings of the Prophet Joseph Smith, Section Six 1843-44, p.340 "But I will take the responsibility upon myself to prophesy in the name of the Lord, that Christ will not come this year, as Father Miller has prophesied, for we have seen the bow; and I also prophesy, in the name of the Lord, that Christ will not come in forty years; and if God ever spoke by my mouth, He will not come in that length of time. Brethren, when you go home, write it down, that it may be remembered." Teachings of the Prophet Joseph Smith, Section Six 1843-44, p.341 In the Dreamtime of Australian Aboriginal mythology, the rainbow snake is the deity governing water. In Amazonian cultures, rainbows have long been associated with malign spirits that cause harm, such as miscarriages and (especially) skin problems. In the Amuesha language of central Peru, certain diseases are called ayona’achartan, meaning "the rainbow hurt my skin". A tradition of closing one's mouth at the sight of a rainbow in order to avoid disease appears to pre- date the Incan empire.[33][34] In New Age and Hindu philosophy, the seven colours of the rainbow represent the seven chakras, from the first chakra (red) to the seventh chakra (violet). [edit] Art Rainbows are generally described as very colourful and peaceful. The rainbow occurs often in paintings. Frequently these have a symbolic or programmatic significance (for example, Albrecht Dürer's Melancholia I). In particular, the rainbow appears regularly in religious art (for example, Joseph Anton Koch's Noah's Thanksoffering). Romantic landscape painters such as Turner and Constable were more concerned with recording fleeting effects of light (for example, Constable's Salisbury Cathedral from the Meadows). Other notable examples appear in work by Hans Memling, Caspar David Friedrich, and Peter Paul Rubens.

The Blind Girl, oil painting (1856) by John Everett Millais. The rainbow – one of the beauties of nature that the blind Noah's Thanksoffering (c. 1803) by Joseph Anton Koch. Noah girl cannot experience – is used builds an altar to the Lord after being delivered from the Flood; to underline the pathos of her God sends the rainbow as a sign of his covenant (Genesis 8–9). condition. [edit] Literature The rainbow inspires metaphor and simile. Virginia Woolf in To the Lighthouse highlights the transience of life and Man's mortality through Mrs Ramsey's thought, "it was all as ephemeral as a rainbow" Wordsworth's 1802 poem "My Heart Leaps Up" begins: My heart leaps up when I behold A rainbow in the sky: So was it when my life began; So is it now I am a man; So be it when I shall grow old, Or let me die!... The Newtonian deconstruction of the rainbow is said to have provoked John Keats to lament in his 1820 poem "Lamia": Do not all charms fly At the mere touch of cold philosophy? There was an awful rainbow once in heaven: We know her woof, her texture; she is given In the dull catalogue of common things. Philosophy will clip an Angel's wings, Conquer all mysteries by rule and line, Empty the haunted air, and gnomed mine – Unweave a rainbow In contrast to this is Richard Dawkins; talking about his book Unweaving the Rainbow: Science, Delusion and the Appetite for Wonder: "My title is from Keats, who believed that Newton had destroyed all the poetry of the rainbow by reducing it to the prismatic colours. Keats could hardly have been more wrong, and my aim is to guide all who are tempted by a similar view, towards the opposite conclusion. Science is, or ought to be, the inspiration for great poetry." [edit] Music • In Rainbow Connection, a song known for being sung by Kermit the Frog, the idea of a rainbow is seen as something to wish on, as it is popularly seen as a vision, or symbol of hope. • In End of the Rainbow by September, the singer sings about the rainbow, and how she will be at the end of the rainbow and her ex could see her there when he reaches the end of the rainbow. • End of the Rainbow is an award winning stage play with music (or musical drama) by Peter Quilter. • The group Rainbow and the song Rainbow Demon by Uriah Heep. • I Can Sing a Rainbow is a popular children's classic song written by Arthur Hamilton, despite the name of the song, not all the colours mentioned are actually colours of the rainbow. • Ronnie James Dio used rainbows as a thematic element in many of his songs, particularly as singer and lyrics-writer for Ritchie Blackmore's band Rainbow. Most notable among these are the songs Catch the Rainbow, Rainbow Eyes and the Dio song Rainbow in the Dark. • The band Radiohead released an album in 2007 named, In Rainbows. • The South Korean band Rainbow • Somewhere Over the Rainbow , a song sung by the character Dorothy (Judy Garland) in the musical film The Wizard of Oz. • Japanese singer, Ayumi Hamasaki, has an album named RAINBOW with the same song name. [edit] Films • In A Shine of Rainbows, the young protagonist is promised to be taken into a rainbow. • In Marianne, a double rainbow was filmed by chance when Sandra is introduced for the first time. • In Rainbow, damage to a rainbow threatens the world at large. • In the film The Wizard of Oz, lead character Dorothy Gale sings the song "Over the Rainbow" where she fantasises about a place over the rainbow, where the world is in peace and harmony. [edit] Flags Main article: Rainbow flag Rainbow flags tend to be used as a sign of a new era, of hope, or of social change. Rainbow flags have been used in many places over the centuries: in the German Peasants' War in the 16th century, as a symbol of the Cooperative movement; as a symbol of peace, especially in Italy; to represent the Tawantin Suyu, or Inca territory, mainly in Peru and Bolivia;[35] by some Druze communities in the Middle east; by the Jewish Autonomous Oblast; to represent the International Order of Rainbow for Girls since the early 1920s; and as a symbol of gay pride and LGBT social movements since the 1970s.[36][37] [edit] See also • Atmospheric optics • Circumzenithal arc • Fog bow • Glory • Halo • Iridescent colours in soap bubbles • Moonbow • Sun dog [edit] Notes 1. ^ Walklet, Keith S. (2006). "Lunar Rainbows - When to View and How to Photograph a "Moonbow"". The Ansel Adams Gallery. Archived from the original on May 25, 2007. Retrieved 2007-06-07. 2. ^ Berlin, B. and Kay, P. (1969). Basic Color Terms: Their Universality and Evolution. Berkeley: University of California Press. ISBN 1575861623. 3. ^ "Umn.edu". Umn.edu. Retrieved 2010-10-16. 4. ^ Cowley, Les. "Sea Water Rainbow". Atmospheric Optics. Retrieved 2007-06- 07. 5. ^ Cowley, Les. "Zero order glow". Atmospheric Optics. Retrieved 2011-08-08. 6. ^ Großmann, Michael. "Natural tertiary rainbow". Atmospheric Optics. Retrieved 2011-08-08. 7. ^ Billet, Felix (1868). "Mémoire sur les Dix-neuf premiers arcs-en-ciel de l'eau". Annales scientifiques de l'École Normale Supérieure 1 (5): 67–109. Retrieved 2008-11- 25. 8. ^ Walker, Jearl (1977). "How to create and observe a dozen rainbows in a single drop of water". Scientific American 237 (July): 138–144 + 154. Retrieved 2011-08-08. 9. ^ Ng, P. H.; Tse, M. Y.; Lee, W. K. (1998). "Observation of high-order rainbows formed by a pendant drop". Journal of the Optical Society of America B 15 (11): 2782. Bibcode 1998JOSAB..15.2782N. doi:10.1364/JOSAB.15.002782. 10. ^ Terje O. Nordvik. "Six Rainbows Across Norway". APOD (Astronomy Picture of the Day). Retrieved 2007-06-07. 11. ^ Cowley, Les. "Circumhorizontal arc". Atmospheric Optics. Retrieved 2007-04- 22. 12. ^ Science@NASA. "Rainbows on Titan". Retrieved 2008-11-25. 13. ^ Raymond L. Lee, Alistair B. Fraser (2001). The rainbow bridge: rainbows in art, myth, and science. Penn State Press. p. 109. ISBN 0271019778. 14. ^ a b c Topdemir, Hüseyin Gazi (2007). "Kamal Al-Din Al-Farisi’s Explanation of the Rainbow". Humanity & Social Sciences Journal 2 (1): 75–85 [77]. Retrieved 2008- 09-16. 15. ^ a b O'Connor, J.J.; Robertson, E.F. (November 1999). "Kamal al-Din Abu'l Hasan Muhammad Al-Farisi". MacTutor History of Mathematics archive, University of St Andrews. Retrieved 2007-06-07. 16. ^ Topdemir, Hüseyin Gazi (2007). "Kamal Al-Din Al-Farisi's Explanation of the Rainbow". Humanity & Social Sciences Journal 2 (1): 75–85 [83]. Retrieved 2008-09-16. 17. ^ a b Raymond L. Lee, Alistair B. Fraser (2001). The rainbow bridge: rainbows in art, myth, and science. Penn State Press. pp. 141–144 ISBN =0271019778. ISBN 9780271019772. 18. ^ Carl Benjamin Boyer (1954). "Robert Grosseteste on the Rainbow". Osiris 11: 247–258. 19. ^ Sivin, Nathan (1995). Science in Ancient China: Researches and Reflections Brookfield, Vermont: VARIORUM. III: Ashgate Publishing.. p. 24. 20. ^ Dong, Paul (2000). China's Major Mysteries: Paranormal Phenomena and the Unexplained in the People's Republic. San Francisco: China Books and Periodicals, Inc.. p. 72. ISBN 0-8351-2676-5. 21. ^ Nader El-Bizri (2005). "Ibn al-Haytham". In Thomas F. Glick, Steven J. Livesey, and Faith Wallis. Medieval Science, Technology, and Medicine: An Encyclopedia. New York — London: Routledge. pp. 237–240. 22. ^ Nader El-Bizri (2005). "Optics". In Josef W. Meri. Medieval Islamic Civilization: An Encyclopedia. II. New York – London: Routledge. pp. 578–580. 23. ^ Nader El-Bizri, (2006). "Al-Farisi, Kamal al-Din". In Oliver Leaman. The Biographical Encyclopaedia of Islamic Philosophy. I. London — New York: Thoemmes Continuum. pp. 131–135. 24. ^ Nader El-Bizri (2006). "Ibn al-Haytham, al-Hasan". In Oliver Leaman. The Biographical Encyclopaedia of Islamic Philosophy. I. London — New York: Thoemmes Continuum. pp. 248–255. 25. ^ Davidson, Michael W. (August 1, 2003). "Roger Bacon (1214–1294)". Florida State University. Retrieved 2006-08-10. 26. ^ Raymond L. Lee, Alistair B. Fraser (2001). The rainbow bridge: rainbows in art, myth, and science. p. 156. ISBN 9780271019772. 27. ^ Lindberg, David C (Summer, 1966). "Roger Bacon's Theory of the Rainbow: Progress or Regress?". Isis 57 (2): 235. doi:10.1086/350116. 28. ^ Boyer, Carl B. (1952). "Descartes and the Radius of the Rainbow". Isis 43 (2): 95–98. doi:10.1086/349399. 29. ^ Gedzelman, Stanley David (1989). "Did Kepler's Supplement to Witelo Inspire Descartes' Theory of the Rainbow?". Bulletin of the American Meteorological Society 70 (7): 750. Bibcode 1989BAMS...70..750G. doi:10.1175/1520- 0477(1989)070<0750:DKSTWI>2.0.CO;2. 30. ^ O'Connor, J.J.; Robertson, E.F. (January 2000). "Sir Isaac Newton". University of St. Andrews. Retrieved 2007-06-19. 31. ^ Nussenzveig, H. Moyses (1977). "The Theory of the Rainbow". Scientific American 236 (4): 116. 32. ^ Holy Bible: (King James Version.) (2004). Intellectual Reserve, inc. 33. ^ Céline Valadeau, Joaquina Alban Castillo, Michel Sauvain, Augusto Francis Lorese and Geneviève Bourdy (January 8, 2010). "The rainbow hurts my skin: Medicinal concepts and plants uses among the Yanesha (Amuesha), an Amazonian Peruvian ethnic group". Journal of Ethnopharmacology 127 (1): 175–192. doi:10.1016/j.jep.2009.09.024. PMID 19835943. 34. ^ Webster, Patty. "Utilizing Western and Traditional Remedies in the Peruvian Amazon". 35. ^ "Flagspot.net". Flagspot.net. Retrieved 2010-10-16. 36. ^ The Rainbow Flag. Retrieved 2007-08-21. 37. ^ Gilbert Baker (October 18, 2007). "Pride-Flyin' Flag: Rainbow-flag founder marks 30-years anniversary". Metro Weekly (Washington DC). Retrieved 2008-03-13. [edit] References • Greenler, Robert (1980). Rainbows, Halos, and Glories. Cambridge University Press. ISBN 0195218337. • Lee, Raymond L. and Alastair B. Fraser (2001). The Rainbow Bridge: Rainbows in Art, Myth and Science. New York: Pennsylvania State University Press and SPIE Press. ISBN 0-271-01977-8. • Lynch, David K.; Livingston, William (2001). Color and Light in Nature (2nd ed.). Cambridge University Press. ISBN 0-521-77504-3. • Minnaert, Marcel G.J.; Lynch, David K.; Livingston, William (1993). Light and Color in the Outdoors. Springer-Verlag. ISBN 0-387-97935-2. • Minnaert, Marcel G.J.; Lynch, David K.; Livingston, William (1973). The Nature of Light and Color in the Open Air. Dover Publications. ISBN 0-486-20196-1. • Naylor, John; Lynch, David K.; Livingston, William (2002). Out of the Blue: A 24-Hour Skywatcher's Guide. Cambridge University Press. ISBN 0-521-80925-8. • Boyer, Carl B. (1987). The Rainbow, From Myth to Mathematics. Princeton University Press. ISBN 0-691-08457-2. • Graham, Lanier F., ed (1976). The Rainbow Book. Berkeley, California: Shambhala Publications and The Fine Arts Museums of San Francisco. (Large format handbook for the Summer 1976 exhibition The Rainbow Art Show which took place primarily at the De Young Museum but also at other museums. The book is divided into seven sections, each coloured a different colour of the rainbow.) • De Rico, Ul (1978). The Rainbow Goblins. Thames & Hudson. ISBN 0-500-27759-1. [edit] External links

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• Images by Crayford Manor House Astronomical Society • National Center for Atmospheric Research, About Rainbows • Supernumerary and Multiple Rainbows • Incredible Rainbows Worldwide - slideshow by Life magazine • Interactive simulation of light refraction in a drop (java applet) • Spectacular rainbow at Elam Bend (McFall, Missouri) • Walter Lewin's Discussion on colours and rainbow physics • Straight Dope on double rainbows • Rare photo of the ‘end’ of the rainbow • Rainbow seen through infrared filter and through ultraviolet filter • Double Rainbow (viral video) • Atmospheric Optics website by Les Cowley - Description of multiple types of bows, including: "bows that cross, red bows, twinned bows, coloured fringes, dark bands, spokes", etc. Diamond From Wikipedia, the free encyclopedia This article is about the mineral. For the gemstone, see Diamond (gemstone). For other uses, including the shape ◊, see Diamond (disambiguation).

Diamond

The slightly misshapen octahedral shape of this rough diamond crystal in matrix is typical of the mineral. Its lustrous faces also indicate that this crystal is from a primary deposit. General Category Native Minerals Chemical C formula Strunz 01.CB.10a classification Identification Molar mass 12.01 g·mol -1 Typically yellow, brown or gray to colorless. Less often blue, green, Color black, translucent white, pink, violet, orange, purple and red. Crystal habit Octahedral Crystal system Isometric-Hexoctahedral (Cubic) Cleavage 111 (perfect in four directions) Fracture Conchoidal (shell-like) Mohs scale 10 hardness Luster Adamantine Streak Colorless Transparent to subtransparent to Diaphaneity translucent Specific gravity 3.52±0.01 Density 3.5–3.53 g/cm 3 Polish luster Adamantine Optical Isotropic properties Refractive index 2.418 (at 500 nm) Birefringence None Pleochroism None Dispersion 0.044 Melting point Pressure dependent References [1][2]

In mineralogy, diamond (from the ancient Greek αδάμας – adámas "unbreakable") is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions. Diamond is renowned as a material with superlative physical qualities, most of which originate from the strong covalent bonding between its atoms. In particular, diamond has the highest hardness and thermal conductivity of any bulk material. Those properties determine the major industrial application of diamond in cutting and polishing tools. Diamond has remarkable optical characteristics. Because of its extremely rigid lattice, it can be contaminated by very few types of impurities, such as boron and nitrogen. Combined with wide transparency, this results in the clear, colorless appearance of most natural diamonds. Small amounts of defects or impurities (about one per million of lattice atoms) color diamond blue (boron), yellow (nitrogen), brown (lattice defects), green (radiation exposure), purple, pink, orange or red. Diamond also has relatively high optical dispersion (ability to disperse light of different colors), which results in its characteristic luster. Excellent optical and mechanical properties, combined with efficient marketing, make diamond the most popular gemstone. Most natural diamonds are formed at high-pressure high-temperature conditions existing at depths of 140 to 190 kilometers (87 to 120 mi) in the Earth mantle. Carbon-containing minerals provide the carbon source, and the growth occurs over periods from 1 billion to 3.3 billion years (25% to 75% of the age of the Earth). Diamonds are brought close to the Earth surface through deep volcanic eruptions by a magma, which cools into igneous rocks known as kimberlites and lamproites. Diamonds can also be produced synthetically in a high-pressure high-temperature process which approximately simulates the conditions in the Earth mantle. An alternative, and completely different growth technique is chemical vapor deposition (CVD). Several non- diamond materials, which include cubic zirconia and silicon carbide and are often called diamond simulants, resemble diamond in appearance and many properties. Special gemological techniques have been developed to distinguish natural and synthetic diamonds and diamond simulants. Contents [hide] • 1 History • 2 Material properties o 2.1 Hardness o 2.2 Electrical conductivity o 2.3 Surface property o 2.4 Chemical stability o 2.5 Color o 2.6 Identification • 3 Natural history o 3.1 Formation in cratons o 3.2 Space diamonds o 3.3 Transport from mantle • 4 Production o 4.1 Controversial sources • 5 Commercial markets o 5.1 Gemstones and their distribution . 5.1.1 Marketing . 5.1.2 Cutting o 5.2 Industrial uses • 6 Synthetics, simulants, and enhancements o 6.1 Synthetics o 6.2 Simulants o 6.3 Enhancements o 6.4 Identification • 7 See also • 8 References • 9 Books • 10 External links History See also: Diamond (gemstone) The name diamond is derived from the ancient Greek αδάμας (adámas), "proper", "unalterable", "unbreakable", "untamed", from ἀ - (a-), "un-" + δαμάω (damáō), "I overpower", "I tame".[3] Diamonds are thought to have been first recognized and mined in India, where significant alluvial deposits of the stone could be found many centuries ago along the rivers Penner, Krishna and Godavari. Diamonds have been known in India for at least 3,000 years but most likely 6,000 years.[4] Diamonds have been treasured as gemstones since their use as religious icons in ancient India. Their usage in engraving tools also dates to early human history.[5][6] The popularity of diamonds has risen since the 19th century because of increased supply, improved cutting and polishing techniques, growth in the world economy, and innovative and successful advertising campaigns. [7] In 1772, Antoine Lavoisier used a lens to concentrate the rays of the sun on a diamond in an atmosphere of oxygen, and showed that the only product of the combustion was carbon dioxide, proving that diamond is composed of carbon. Later in 1797, Smithson Tennant repeated and expanded that experiment. By demonstrating that burning diamond and graphite releases the same amount of gas he established the chemical equivalence of these substances.[8] The most familiar use of diamonds today is as gemstones used for adornment, a use which dates back into antiquity. The dispersion of white light into spectral colors is the primary gemological characteristic of gem diamonds. In the 20th century, experts in gemology have developed methods of grading diamonds and other gemstones based on the characteristics most important to their value as a gem. Four characteristics, known informally as the four Cs, are now commonly used as the basic descriptors of diamonds: these are carat, cut, color, and clarity.[9] A large, flawless diamond is known as a paragon. Material properties Main articles: Material properties of diamond and Crystallographic defects in diamond

Theoretically predicted phase diagram of carbon Diamond and graphite are two allotropes of carbon: pure forms of the same element that differ in structure. A diamond is a transparent crystal of tetrahedrally bonded carbon atoms ( sp 3) that crystallizes into the diamond lattice which is a variation of the face centered cubic structure. Diamonds have been adapted for many uses because of the material's exceptional physical characteristics. Most notable are its extreme hardness and thermal conductivity (900–2,320 W·m−1·K−1),[10] as well as wide bandgap and high optical dispersion.[11] Above 1,700 °C (1,973 K / 3,583 °F) in vacuum or oxygen-free atmosphere, diamond converts to graphite; in air, transformation starts at ~700 °C.[12] Diamond's ignition point is 720 - 800 °C in oxygen and 850 - 1,000 °C in air.[13] Naturally occurring diamonds have a density ranging from 3.15–3.53 g/cm3, with pure diamond close to 3.52 g/cm3.[1] The chemical bonds that hold the carbon atoms in diamonds together are weaker than those in graphite. In diamonds, the bonds form an inflexible three-dimensional lattice, whereas in graphite, the atoms are tightly bonded into sheets, which can slide easily over one another, making the overall structure weaker.[14] Hardness Diamond is the hardest known natural material on the Mohs scale of mineral hardness, where hardness is defined as resistance to scratching and is graded between 1 (softest) and 10 (hardest). Diamond has a hardness of 10 (hardest) on this scale.[15] Diamond's hardness has been known since antiquity, and is the source of its name. Diamond hardness depends on its purity, crystalline perfection and orientation: hardness is higher for flawless, pure crystals oriented to the <111> direction (along the longest diagonal of the cubic diamond lattice).[16] Therefore, whereas it might be possible to scratch some diamonds with other materials, such as boron nitride, the hardest diamonds can only be scratched by other diamonds and nanocrystalline diamond aggregates. The hardness of diamond contributes to its suitability as a gemstone. Because it can only be scratched by other diamonds, it maintains its polish extremely well. Unlike many other gems, it is well-suited to daily wear because of its resistance to scratching—perhaps contributing to its popularity as the preferred gem in engagement or wedding rings, which are often worn every day. The hardest natural diamonds mostly originate from the Copeton and Bingara fields located in the New England area in New South Wales, Australia. These diamonds are generally small, perfect to semiperfect octahedra, and are used to polish other diamonds. Their hardness is associated with the crystal growth form, which is single-stage crystal growth. Most other diamonds show more evidence of multiple growth stages, which produce inclusions, flaws, and defect planes in the crystal lattice, all of which affect their hardness. It is possible to treat regular diamonds under a combination of high pressure and high temperature to produce diamonds that are harder than the diamonds used in hardness gauges.[17] Somewhat related to hardness is another mechanical property toughness, which is a material's ability to resist breakage from forceful impact. The toughness of natural diamond has been measured as 7.5–10 MPa·m1/2.[18][19] This value is good compared to other gemstones, but poor compared to most engineering materials. As with any material, the macroscopic geometry of a diamond contributes to its resistance to breakage. Diamond has a cleavage plane and is therefore more fragile in some orientations than others. Diamond cutters use this attribute to cleave some stones, prior to faceting.[20] "Impact toughness" is one of the main indexes to measure the quality of synthetic industrial diamonds.[13] Electrical conductivity Other specialized applications also exist or are being developed, including use as semiconductors: some blue diamonds are natural semiconductors, in contrast to most diamonds, which are excellent electrical insulators.[21] The conductivity and blue color originate from boron impurity. Boron substitutes for carbon atoms in the diamond lattice, donating a hole into the valence band.[21] Substantial conductivity is commonly observed in nominally undoped diamond grown by chemical vapor deposition. This conductivity is associated with hydrogen-related species adsorbed at the surface, and it can be removed by annealing or other surface treatments.[22][23] Surface property Diamonds are lipophilic and hydrophobic, which means the diamonds' surface cannot be wet by water but can be easily wet and stuck by oil. This property can be utilized to extract diamonds using oil when making synthetic diamonds.[13] Chemical stability Diamonds' chemical property is very stable. Under room temperature diamonds do not react with any chemical reagents including various kinds of acid and alkali. Diamonds' surface can only be oxidized a little by just a few oxidants under high temperature (below 1,000 °C). So acid and alkali can be used to refine synthetic diamonds.[13] Color Main article: Diamond color

Brown diamonds at the National Museum of Natural History in Washington, D.C. Diamond has a wide bandgap of 5.5 eV corresponding to the deep ultraviolet wavelength of 225 nanometers. This means pure diamond should transmit visible light and appear as a clear colorless crystal. Colors in diamond originate from lattice defects and impurities. The diamond crystal lattice is exceptionally strong and only atoms of nitrogen, boron and hydrogen can be introduced into diamond during the growth at significant concentrations (up to atomic percents). Transition metals Ni and Co, which are commonly used for growth of synthetic diamond by high-pressure high-temperature techniques, have been detected in diamond as individual atoms; the maximum concentration is 0.01% for Ni[24] and even much less for Co. Virtually any element can be introduced to diamond by ion implantation.[25] Nitrogen is by far the most common impurity found in gem diamonds and is responsible for the yellow and brown color in diamonds. Boron is responsible for the blue color.[11] Color in diamond has two additional sources: irradiation (usually by alpha particles), that causes the color in green diamonds; and plastic deformation of the diamond crystal lattice. Plastic deformation is the cause of color in some brown[26] and perhaps pink and red diamonds.[27] In order of rarity, yellow diamond is followed by brown, colorless, then by blue, green, black, pink, orange, purple, and red.[20] "Black", or Carbonado, diamonds are not truly black, but rather contain numerous dark inclusions that give the gems their dark appearance. Colored diamonds contain impurities or structural defects that cause the coloration, while pure or nearly pure diamonds are transparent and colorless. Most diamond impurities replace a carbon atom in the crystal lattice, known as a carbon flaw. The most common impurity, nitrogen, causes a slight to intense yellow coloration depending upon the type and concentration of nitrogen present.[20] The Gemological Institute of America (GIA) classifies low saturation yellow and brown diamonds as diamonds in the normal color range, and applies a grading scale from "D" (colorless) to "Z" (light yellow). Diamonds of a different color, such as blue, are called fancy colored diamonds, and fall under a different grading scale.[20] In 2008, the Wittelsbach Diamond, a 35.56-carat (7.11 g) blue diamond once belonging to the King of Spain, fetched over US$24 million at a Christie's auction.[28] In May 2009, a 7.03-carat (1.41 g) blue diamond fetched the highest price per carat ever paid for a diamond when it was sold at auction for 10.5 million Swiss francs (6.97 million euro or US$9.5 million at the time).[29] That record was however beaten the same year: a 5-carat (1.0 g) vivid pink diamond was sold for $10.8 million in Hong Kong on December 1, 2009.[30] Identification Diamonds can be identified by their high thermal conductivity. Their high refractive index is also indicative, but other materials have similar refractivity. Diamonds cut glass, but this does not positively identify a diamond because other materials, such as quartz, also lie above glass on the Mohs scale and can also cut it. Diamonds can scratch other diamonds, but this can result in damage to one or both stones. Hardness tests are infrequently used in practical gemology because of their potentially destructive nature.[15] The extreme hardness and high value of diamond means that gems are typically polished slowly using painstaking traditional techniques and greater attention to detail than is the case with most other gemstones;[8] these tend to result in extremely flat, highly polished facets with exceptionally sharp facet edges. Diamonds also possess an extremely high refractive index and fairly high dispersion. Taken together, these factors affect the overall appearance of a polished diamond and most diamantaires still rely upon skilled use of a loupe (magnifying glass) to identify diamonds 'by eye'.[31] Natural history The formation of natural diamond requires very specific conditions—exposure of carbon-bearing materials to high pressure, ranging approximately between 45 and 60 kilobars (4.5 and 6 GPa), but at a comparatively low temperature range between approximately 900–1300 °C. These conditions are met in two places on Earth; in the lithospheric mantle below relatively stable continental plates, and at the site of a meteorite strike.[32] Formation in cratons

One face of an uncut octahedral diamond, showing trigons (of positive and negative relief) formed by natural chemical etching The conditions for diamond formation to happen in the lithospheric mantle occur at considerable depth corresponding to the requirements of temperature and pressure. These depths are estimated between 140 and 190 km though occasionally diamonds have crystallized at depths about 300 km as well.[33] The rate at which temperature changes with increasing depth into the Earth varies greatly in different parts of the Earth. In particular, under oceanic plates the temperature rises more quickly with depth, beyond the range required for diamond formation at the depth required. The correct combination of temperature and pressure is only found in the thick, ancient, and stable parts of continental plates where regions of lithosphere known as cratons exist. Long residence in the cratonic lithosphere allows diamond crystals to grow larger.[33] Through studies of carbon isotope ratios (similar to the methodology used in carbon dating, except with the stable isotopes C-12 and C-13), it has been shown that the carbon found in diamonds comes from both inorganic and organic sources. Some diamonds, known as harzburgitic, are formed from inorganic carbon originally found deep in the Earth's mantle. In contrast, eclogitic diamonds contain organic carbon from organic detritus that has been pushed down from the surface of the Earth's crust through subduction (see plate tectonics) before transforming into diamond. These two different source of carbon have measurably different 13C:12C ratios. Diamonds that have come to the Earth's surface are generally quite old, ranging from under 1 billion to 3.3 billion years old. This is 22% to 73% of the age of the Earth.[33] Diamonds occur most often as euhedral or rounded octahedra and twinned octahedra known as macles. As diamond's crystal structure has a cubic arrangement of the atoms, they have many facets that belong to a cube, octahedron, rhombicosidodecahedron, tetrakis hexahedron or disdyakis dodecahedron. The crystals can have rounded off and unexpressive edges and can be elongated. Sometimes they are found grown together or form double "twinned" crystals at the surfaces of the octahedron. These different shapes and habits of some diamonds result from differing external circumstances. Diamonds (especially those with rounded crystal faces) are commonly found coated in nyf, an opaque gum-like skin.[34] Space diamonds Not all diamonds found on Earth originated here. A type of diamond called carbonado that is found in South America and Africa may have been deposited there via an asteroid impact (not formed from the impact) about 3 billion years ago. These diamonds may have formed in the intrastellar environment, but as of 2008, there was no scientific consensus on how carbonado diamonds originated.[35][36] Diamonds can also form under other naturally occurring high-pressure conditions. Very small diamonds of micrometer and nanometer sizes, known as microdiamonds or nanodiamonds respectively, have been found in meteorite impact craters. Such impact events create shock zones of high pressure and temperature suitable for diamond formation. Impact-type microdiamonds can be used as an indicator of ancient impact craters.[32] Scientific evidence indicates that white dwarf stars have a core of crystallized carbon and oxygen nuclei. The largest of these found in the universe so far, BPM 37093, is located 50 light-years (4.7×1014 km) away in the constellation Centaurus. A news release from the Harvard- Smithsonian Center for Astrophysics described the 2,500-mile (4,000 km)-wide stellar core as a diamond.[37] It was referred to as Lucy, after the Beatles' song "Lucy in the Sky With Diamonds". [17][38] Transport from mantle

Schematic diagram of a volcanic pipe Diamond-bearing rock is carried from the mantle to the Earth's surface by deep-origin volcanic eruptions. The magma for such a volcano must originate at a depth where diamonds can be formed[33]—150 km (93 mi) or more (three times or more the depth of source magma for most volcanoes). This is a relatively rare occurrence. These typically small surface volcanic craters extend downward in formations known as volcanic pipes.[33] The pipes contain material that was transported toward the surface by volcanic action, but was not ejected before the volcanic activity ceased. During eruption these pipes are open to the surface, resulting in open circulation; many xenoliths of surface rock and even wood and fossils are found in volcanic pipes. Diamond- bearing volcanic pipes are closely related to the oldest, coolest regions of continental crust (cratons). This is because cratons are very thick, and their lithospheric mantle extends to great enough depth that diamonds are stable. Not all pipes contain diamonds, and even fewer contain enough diamonds to make mining economically viable.[33] The magma in volcanic pipes is usually one of two characteristic types, which cool into igneous rock known as either kimberlite or lamproite.[33] The magma itself does not contain diamond; instead, it acts as an elevator that carries deep-formed rocks (xenoliths), minerals (xenocrysts), and fluids upward. These rocks are characteristically rich in magnesium-bearing olivine, pyroxene, and amphibole minerals[33] which are often altered to serpentine by heat and fluids during and after eruption. Certain indicator minerals typically occur within diamantiferous kimberlites and are used as mineralogical tracers by prospectors, who follow the indicator trail back to the volcanic pipe which may contain diamonds. These minerals are rich in chromium (Cr) or titanium (Ti), elements which impart bright colors to the minerals. The most common indicator minerals are chromium garnets (usually bright red chromium-pyrope, and occasionally green ugrandite-series garnets), eclogitic garnets, orange titanium-pyrope, red high-chromium spinels, dark chromite, bright green chromium-diopside, glassy green olivine, black picroilmenite, and magnetite. Kimberlite deposits are known as blue ground for the deeper serpentinized part of the deposits, or as yellow ground for the near surface smectite clay and carbonate weathered and oxidized portion.[33] Once diamonds have been transported to the surface by magma in a volcanic pipe, they may erode out and be distributed over a large area. A volcanic pipe containing diamonds is known as a primary source of diamonds. Secondary sources of diamonds include all areas where a significant number of diamonds have been eroded out of their kimberlite or lamproite matrix, and accumulated because of water or wind action. These include alluvial deposits and deposits along existing and ancient shorelines, where loose diamonds tend to accumulate because of their size and density. Diamonds have also rarely been found in deposits left behind by glaciers (notably in Wisconsin and Indiana); in contrast to alluvial deposits, glacial deposits are minor and are therefore not viable commercial sources of diamond.[33] Production See also: List of diamond mines and Exploration diamond drilling Approximately 130,000,000 carats (26,000 kg) of diamonds are mined annually, with a total value of nearly US$9 billion, and about 100,000 kg (220,000 lb) are synthesized annually.[39] Roughly 49% of diamonds originate from Central and Southern Africa, although significant sources of the mineral have been discovered in Canada, India, Russia, Brazil, and Australia.[40] They are mined from kimberlite and lamproite volcanic pipes, which can bring diamond crystals, originating from deep within the Earth where high pressures and temperatures enable them to form, to the surface. The mining and distribution of natural diamonds are subjects of frequent controversy such as concerns over the sale of blood diamonds or conflict diamonds by African paramilitary groups.[41] The diamond supply chain is controlled by a limited number of powerful businesses, and is also highly concentrated in a small number of locations around the world. Only a very small fraction of the diamond ore consists of actual diamonds. The ore is crushed, during which care is required not to destroy larger diamonds, and then sorted by density. Today, diamonds are located in the diamond-rich density fraction with the help of X-ray fluorescence, after which the final sorting steps are done by hand. Before the use of X-rays became commonplace,[42] the separation was done with grease belts; diamonds have a stronger tendency to stick to grease than the other minerals in the ore.[20] Historically, diamonds were found only in alluvial deposits in Guntur and Krishna district of the Krishna River delta in Southern India.[43] India led the world in diamond production from the time of their discovery in approximately the 9th century BC[4][44] to the mid-18th century AD, but the commercial potential of these sources had been exhausted by the late 18th century and at that time India was eclipsed by Brazil where the first non-Indian diamonds were found in 1725.[4] Currently, one of the most prominent Indian mines is located at Panna.[45] Diamond extraction from primary deposits (kimberlites and lamproites) started in the 1870s after the discovery of the Diamond Fields in South Africa.[46] Production has increased over time and now an accumulated total of 4,500,000,000 carats (900,000 kg) have been mined since that date. [47] Twenty percent of that amount has been mined in the last five years, and during the last 10 years, nine new mines have started production; four more are waiting to be opened soon. Most of these mines are located in Canada, Zimbabwe, Angola, and one in Russia.[47] In the U.S., diamonds have been found in Arkansas, Colorado, and Montana.[48][49] In 2004, the discovery of a microscopic diamond in the U.S. led to the January 2008 bulk-sampling of kimberlite pipes in a remote part of Montana.[49] Today, most commercially viable diamond deposits are in Russia (mostly in Sakha Republic, for example Mir pipe and Udachnaya pipe), Botswana, Australia (Northern and Western Australia) and the Democratic Republic of Congo.[50] In 2005, Russia produced almost one-fifth of the global diamond output, reports the British Geological Survey. Australia boasts the richest diamantiferous pipe, with production from the Argyle diamond mine reaching peak levels of 42 metric tons per year in the 1990s.[48][51] There are also commercial deposits being actively mined in the Northwest Territories of Canada and Brazil.[40] Diamond prospectors continue to search the globe for diamond-bearing kimberlite and lamproite pipes. Controversial sources Main articles: Kimberley Process, Blood diamond, and Child labour in the diamond industry In some of the more politically unstable central African and west African countries, revolutionary groups have taken control of diamond mines, using proceeds from diamond sales to finance their operations. Diamonds sold through this process are known as conflict diamonds or blood diamonds.[41] Major diamond trading corporations continue to fund and fuel these conflicts by doing business with armed groups. In response to public concerns that their diamond purchases were contributing to war and human rights abuses in central and western Africa, the United Nations, the diamond industry and diamond-trading nations introduced the Kimberley Process in 2002.[52] The Kimberley Process aims to ensure that conflict diamonds do not become intermixed with the diamonds not controlled by such rebel groups. This is done by requiring diamond- producing countries to provide proof that the money they make from selling the diamonds is not used to fund criminal or revolutionary activities. Although the Kimberley Process has been moderately successful in limiting the number of conflict diamonds entering the market, some still find their way in. Conflict diamonds constitute 2–3% of all diamonds traded.[53] Two major flaws still hinder the effectiveness of the Kimberley Process: (1) the relative ease of smuggling diamonds across African borders, and (2) the violent nature of diamond mining in nations that are not in a technical state of war and whose diamonds are therefore considered "clean".[52] The Canadian Government has set up a body known as Canadian Diamond Code of Conduct[54] to help authenticate Canadian diamonds. This is a stringent tracking system of diamonds and helps protect the "conflict free" label of Canadian diamonds.[55] Commercial markets See also: Diamonds as an investment A round brilliant cut diamond set in a ring The diamond industry can be separated into two distinct categories: one dealing with gem-grade diamonds and another for industrial-grade diamonds. While a large trade in both types of diamonds exists, the two markets act in dramatically different ways. Gemstones and their distribution Main article: Diamond (gemstone) A large trade in gem-grade diamonds exists. Unlike other commodities, such as most precious metals, there is a substantial mark-up in the retail sale of gem diamonds.[56] There is a well- established market for resale of polished diamonds (e.g. pawnbroking, auctions, second-hand jewelry stores, diamantaires, bourses, etc.). One hallmark of the trade in gem-quality diamonds is its remarkable concentration: wholesale trade and diamond cutting is limited to just a few locations; In 2003, 92% of the world's diamonds were cut and polished in Surat, India.[57] Other important centers of diamond cutting and trading are the Antwerp diamond district in Belgium, where the International Gemological Institute is based, London, the Diamond District in New York City, Tel Aviv, and Amsterdam. A single company—De Beers—controls a significant proportion of the trade in diamonds.[58] They are based in Johannesburg, South Africa and London, England. One contributory factor is the geological nature of diamond deposits: several large primary kimberlite-pipe mines each account for significant portions of market share (such as the Jwaneng mine in Botswana, which is a single large pit operated by De Beers that can produce between 12,500,000 carats (2,500 kg) to 15,000,000 carats (3,000 kg) of diamonds per year,[59]) whereas secondary alluvial diamond deposits tend to be fragmented amongst many different operators because they can be dispersed over many hundreds of square kilometers (e.g., alluvial deposits in Brazil). The production and distribution of diamonds is largely consolidated in the hands of a few key players, and concentrated in traditional diamond trading centers, the most important being Antwerp, where 80% of all rough diamonds, 50% of all cut diamonds and more than 50% of all rough, cut and industrial diamonds combined are handled.[60] This makes Antwerp a de facto "world diamond capital".[61] Another important diamond center is New York City, where almost 80% of the world's diamonds are sold, including auction sales.[60] The DeBeers company, as the world's largest diamond miner holds a dominant position in the industry, and has done so since soon after its founding in 1888 by the British imperialist Cecil Rhodes. De Beers owns or controls a significant portion of the world's rough diamond production facilities (mines) and distribution channels for gem-quality diamonds. The Diamond Trading Company (DTC) is a subsidiary of De Beers and markets rough diamonds from De Beers-operated mines. De Beers and its subsidiaries own mines that produce some 40% of annual world diamond production. For most of the 20th century over 80% of the world's rough diamonds passed through De Beers,[62] but in the period 2001–2009 the figure has decreased to around 45%.[63] De Beers sold off the vast majority of its diamond stockpile in the late 1990s – early 2000s[64] and the remainder largely represents working stock (diamonds that are being sorted before sale).[65] This was well documented in the press[66] but remains little known to the general public. As a part of reducing its influence, De Beers withdrew from purchasing diamonds on the open market in 1999 and ceased, at the end of 2008, purchasing Russian diamonds mined by the largest Russian diamond company Alrosa.[67] As at January 2011, De Beers states that it only sells diamonds from the following four countries: Botswana, Namibia, South Africa and Canada.[68] Alrosa had to suspend their sales in October 2008 due to the global energy crisis,[69] but the company reported that it had resumed selling rough diamonds on the open market by October 2009.[70] Apart from Alrosa, other important diamond mining companies include BHP Billiton, which is the world's largest mining company;[71] Rio Tinto Group, the owner of Argyle (100%), Diavik (60%), and Murowa (78%) diamond mines;[72] and Petra Diamonds, the owner of several major diamond mines in Africa. Further down the supply chain, members of The World Federation of Diamond Bourses (WFDB) act as a medium for wholesale diamond exchange, trading both polished and rough diamonds. The WFDB consists of independent diamond bourses in major cutting centers such as Tel Aviv, Antwerp, Johannesburg and other cities across the USA, Europe and Asia.[20] In 2000, the WFDB and The International Diamond Manufacturers Association established the World Diamond Council to prevent the trading of diamonds used to fund war and inhumane acts. WFDB's additional activities include sponsoring the World Diamond Congress every two years, as well as the establishment of the International Diamond Council (IDC) to oversee diamond grading. Once purchased by Sightholders (which is a trademark term referring to the companies that have a three-year supply contract with DTC), diamonds are cut and polished in preparation for sale as gemstones ('industrial' stones are regarded as a by-product of the gemstone market; they are used for abrasives).[73] The cutting and polishing of rough diamonds is a specialized skill that is concentrated in a limited number of locations worldwide.[73] Traditional diamond cutting centers are Antwerp, Amsterdam, Johannesburg, New York City, and Tel Aviv. Recently, diamond cutting centers have been established in China, India, Thailand, Namibia and Botswana.[73] Cutting centers with lower cost of labor, notably Surat in Gujarat, India, handle a larger number of smaller carat diamonds, while smaller quantities of larger or more valuable diamonds are more likely to be handled in Europe or North America. The recent expansion of this industry in India, employing low cost labor, has allowed smaller diamonds to be prepared as gems in greater quantities than was previously economically feasible.[60] Diamonds which have been prepared as gemstones are sold on diamond exchanges called bourses. There are 26 registered diamond bourses in the world.[74] Bourses are the final tightly controlled step in the diamond supply chain; wholesalers and even retailers are able to buy relatively small lots of diamonds at the bourses, after which they are prepared for final sale to the consumer. Diamonds can be sold already set in jewelry, or sold unset ("loose"). According to the Rio Tinto Group, in 2002 the diamonds produced and released to the market were valued at US$9 billion as rough diamonds, US$14 billion after being cut and polished, US$28 billion in wholesale diamond jewelry, and US$57 billion in retail sales.[75] Marketing The image of diamond as a valuable commodity has been preserved through clever marketing campaigns (as, indeed, is the case with many other luxury products). In particular, the De Beers diamond advertising campaign is acknowledged as one of the most successful campaigns in history.[citation needed] N. W. Ayer & Son, the advertising firm retained by De Beers in the mid-20th century, succeeded in reviving the American diamond market and opened up new markets, even in countries where no diamond tradition had existed before. N. W. Ayer's multifaceted marketing campaign included product placement, advertising the diamond itself rather than the De Beers brand, and building associations with celebrities and royalty. It was a "generic" advertising campaign that tended to focus upon promoting diamonds in general, or particular types of diamond jewellery, rather than specific brands. This meant that, as De Beers' market share declined, it was increasingly advertising its competitors' products as well as its own[76] (De Beers' market share dipped temporarily to 2nd place in the global market below Alrosa in the aftermath of the global economic crisis of 2008, down to less than 29% in terms of carats mined, rather than sold[77]). The campaign lasted for decades but was effectively discontinued by early 2011. De Beers still advertises diamonds, but the advertising now mostly promotes its own brands, or licensed product lines, rather than completely "generic" diamond products.[77] The campaign was perhaps best captured by the slogan "a diamond is forever".[7] This slogan is now being used by De Beers Diamond Jewelers,[78] a jewelry firm which is a 50%/50% joint venture between the De Beers mining company and LVMH, the luxury goods conglomerate. Another example of successful diamond marketing is brown Australian diamonds. Brown- colored diamonds have always constituted a significant part of the diamond production, but were considered worthless for jewelry; they were not even assessed on the diamond color scale, and were predominantly used for industrial purposes. The attitude has changed drastically after the development of Argyle diamond mine in Australia in 1986. As a result of an aggressive marketing campaign, brown diamonds have become acceptable gems.[79][80] The change was mostly due to the numbers: the Argyle mine, with its 35,000,000 carats (7,000 kg) of diamonds per year, makes about one-third of global production of natural diamonds;[81] 80% of Argyle diamonds are brown.[82] Cutting Main articles: Diamond cutting and Diamond cut

The Darya-I-Nur Diamond—an example of unusual diamond cut and jewelry arrangement The mined rough diamonds are converted into gems through a multi-step process called "cutting". Diamonds are extremely hard, but also brittle and can be split up by a single blow. Therefore, diamond cutting is traditionally considered as a delicate procedure requiring skills, scientific knowledge, tools and experience. Its final goal is to produce a faceted jewel where the specific angles between the facets would optimize the diamond luster, that is dispersion of white light, whereas the number and area of facets would determine the weight of the final product. The weight reduction upon cutting is significant and can be of the order of 50%.[42] Several possible shapes are considered, but the final decision is often determined not only by scientific, but also practical considerations. For example the diamond might be intended for display or for wear, in a ring or a necklace, singled or surrounded by other gems of certain color and shape.[83] The most time-consuming part of the cutting is the preliminary analysis of the rough stone. It needs to address a large number of issues, bears much responsibility, and therefore can last years in case of unique diamonds. The following issues are considered: • The hardness of diamond and its ability to cleave strongly depend on the crystal orientation. Therefore, the crystallographic structure of the diamond to be cut is analyzed using X-ray diffraction to choose the optimal cutting directions. • Most diamonds contain visible non-diamond inclusions and crystal flaws. The cutter has to decide which flaws are to be removed by the cutting and which could be kept. • The diamond can be split by a single, well calculated blow of a hammer to a pointed tool, which is quick, but risky. Alternatively, it can be cut with a diamond saw, which is a more reliable but tedious procedure.[83][84] After initial cutting, the diamond is shaped in numerous stages of polishing. Unlike cutting, which is a responsible but quick operation, polishing removes material by gradual erosion and is extremely time consuming. The associated technique is well developed; it is considered as a routine and can be performed by technicians.[85] After polishing, the diamond is reexamined for possible flaws, either remaining or induced by the process. Those flaws are concealed through various diamond enhancement techniques, such as repolishing, crack filling, or clever arrangement of the stone in the jewelry. Remaining non-diamond inclusions are removed through laser drilling and filling of the voids produced.[15] Industrial uses

A scalpel with synthetic diamond blade Close-up photograph of an angle grinder blade with tiny diamonds shown embedded in the metal The market for industrial-grade diamonds operates much differently from its gem-grade counterpart. Industrial diamonds are valued mostly for their hardness and thermal conductivity, making many of the gemological characteristics of diamonds, such as clarity and color, irrelevant for most applications. This helps explain why 80% of mined diamonds (equal to about 135,000,000 carats (27,000 kg) annually), unsuitable for use as gemstones, are destined for industrial use. In addition to mined diamonds, synthetic diamonds found industrial applications almost immediately after their invention in the 1950s; another 570,000,000 carats (110,000 kg) of synthetic diamond is produced annually for industrial use. Approximately 90% of diamond grinding grit is currently of synthetic origin.[40] The boundary between gem-quality diamonds and industrial diamonds is poorly defined and partly depends on market conditions (for example, if demand for polished diamonds is high, some suitable stones will be polished into low-quality or small gemstones rather than being sold for industrial use). Within the category of industrial diamonds, there is a sub-category comprising the lowest-quality, mostly opaque stones, which are known as bort.[86] Industrial use of diamonds has historically been associated with their hardness; this property makes diamond the ideal material for cutting and grinding tools. As the hardest known naturally occurring material, diamond can be used to polish, cut, or wear away any material, including other diamonds. Common industrial adaptations of this ability include diamond-tipped drill bits and saws, and the use of diamond powder as an abrasive. Less expensive industrial-grade diamonds, known as bort, with more flaws and poorer color than gems, are used for such purposes.[87] Diamond is not suitable for machining ferrous alloys at high speeds, as carbon is soluble in iron at the high temperatures created by high-speed machining, leading to greatly increased wear on diamond tools compared to alternatives.[88] Specialized applications include use in laboratories as containment for high pressure experiments (see diamond anvil cell), high-performance bearings, and limited use in specialized windows.[86] With the continuing advances being made in the production of synthetic diamonds, future applications are becoming feasible. Garnering much excitement is the possible use of diamond as a semiconductor suitable to build microchips, or the use of diamond as a heat sink [89] in electronics. Synthetics, simulants, and enhancements Synthetics Main article: Synthetic diamond

Synthetic diamonds of various colors grown by the high-pressure high-temperature technique Synthetic diamonds are diamonds manufactured in a laboratory, as opposed to diamonds mined from the Earth. The gemological and industrial uses of diamond have created a large demand for rough stones. This demand has been satisfied in large part by synthetic diamonds, which have been manufactured by various processes for more than half a century. However, in recent years it has become possible to produce gem-quality synthetic diamonds of significant size.[33] The majority of commercially available synthetic diamonds are yellow and are produced by so called High Pressure High Temperature (HPHT) processes.[90] The yellow color is caused by nitrogen impurities. Other colors may also be reproduced such as blue, green or pink, which are a result of the addition of boron or from irradiation after synthesis.[91]

Colorless gem cut from diamond grown by chemical vapor deposition Another popular method of growing synthetic diamond is chemical vapor deposition (CVD). The growth occurs under low pressure (below atmospheric pressure). It involves feeding a mixture of gases (typically 1 to 99 methane to hydrogen) into a chamber and splitting them to chemically active radicals in a plasma ignited by microwaves, hot filament, arc discharge, welding torch or laser.[92] This method is mostly used for coatings, but can also produce single crystals several millimeters in size (see picture).[39] At present, the annual production of gem quality synthetic diamonds is only a few thousand carats, whereas the total production of natural diamonds is around 120,000,000 carats (24,000 kg). Despite this fact, a purchaser is more likely to encounter a synthetic when looking for a fancy-colored diamond because nearly all synthetic diamonds are fancy-colored, while only 0.01% of natural diamonds are.[93] Simulants Main article: Diamond simulant

Gem-cut synthetic silicon carbide set in a ring A diamond simulant is defined as a non-diamond material that is used to simulate the appearance of a diamond. Diamond-simulant gems are often referred to as diamante. The most familiar diamond simulant to most consumers is cubic zirconia. The popular gemstone moissanite (silicon carbide) is often treated as a diamond simulant, although it is a gemstone in its own right. While moissanite looks similar to diamond, its main disadvantage as a diamond simulant is that cubic zirconia is far cheaper and arguably equally convincing. Both cubic zirconia and moissanite are produced synthetically.[94] Enhancements Main article: Diamond enhancement Diamond enhancements are specific treatments performed on natural or synthetic diamonds (usually those already cut and polished into a gem), which are designed to better the gemological characteristics of the stone in one or more ways. These include laser drilling to remove inclusions, application of sealants to fill cracks, treatments to improve a white diamond's color grade, and treatments to give fancy color to a white diamond.[95] Coatings are increasingly used to give a diamond simulant such as cubic zirconia a more "diamond-like" appearance. One such substance is diamond-like carbon—an amorphous carbonaceous material that has some physical properties similar to those of the diamond. Advertising suggests that such a coating would transfer some of these diamond-like properties to the coated stone, hence enhancing the diamond simulant. Techniques such as Raman spectroscopy should easily identify such a treatment.[96] Identification Early diamond identification tests included a scratch test relying on the superior hardness of diamond. This test is destructive, as a diamond can scratch diamond, and is rarely used nowadays. Instead, diamond identification relies on its superior thermal conductivity. Electronic thermal probes are widely used in the gemological centers to separate diamonds from their imitations. These probes consist of a pair of battery-powered thermistors mounted in a fine copper tip. One thermistor functions as a heating device while the other measures the temperature of the copper tip: if the stone being tested is a diamond, it will conduct the tip's thermal energy rapidly enough to produce a measurable temperature drop. This test takes about 2–3 seconds.[97] Whereas the thermal probe can separate diamonds from most of their simulants, distinguishing between various types of diamond, for example synthetic or natural, irradiated or non-irradiated, etc., requires more advanced, optical techniques. Those techniques are also used for some diamonds simulants, such as silicon carbide, which pass the thermal conductivity test. Optical techniques can distinguish between natural diamonds and synthetic diamonds. They can also identify the vast majority of treated natural diamonds.[98] "Perfect" crystals (at the atomic lattice level) have never been found, so both natural and synthetic diamonds always possess characteristic imperfections, arising from the circumstances of their crystal growth, that allow them to be distinguished from each other.[99] Laboratories use techniques such as spectroscopy, microscopy and luminescence under shortwave ultraviolet light to determine a diamond's origin.[98] They also use specially made instruments to aid them in the identification process. Two screening instruments are the DiamondSure and the DiamondView, both produced by the DTC and marketed by the GIA.[100] Several methods for identifying synthetic diamonds can be performed, depending on the method of production and the color of the diamond. CVD diamonds can usually be identified by an orange fluorescence. D-J colored diamonds can be screened through the Swiss Gemmological Institute's[101] Diamond Spotter. Stones in the D-Z color range can be examined through the DiamondSure UV/visible spectrometer, a tool developed by De Beers.[99] Similarly, natural diamonds usually have minor imperfections and flaws, such as inclusions of foreign material, that are not seen in synthetic diamonds. See also

Gemology and Jewelry portal

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"A classic example of monpoly that arises fron ownership of a key resource is DeBeers ... which controls about 80 percent of the world's production of diamonds" 59. ^ "Jwaneng". De Beers. Retrieved 2009-04-26. 60. ^ a b c Tichotsky, J. (2000). Russia's Diamond Colony: The Republic of Sakha. Routledge. p. 254. ISBN 90-5702-420-9. 61. ^ "Jews Surrender Gem Trade to Indians". Spiegel Online. May 15, 2006. 62. ^ "Commission Decision of 25 July 2001 declaring a concentration to be compatible with the common market and the EEA Agreement". Case No COMP/M.2333 – De Beers/LVMH. EUR-Lex. 2003. 63. ^ "Business: Changing facets; Diamonds". The Economist 382 (8517): 68. 2007. 64. ^ "The Elusive Sparcle". The Gem & Jewellery Export Promotion Council. Retrieved 2009-04-26. 65. ^ Even-Zohar, C. (2008-11-06). "Crisis Mitigation at De Beers". DIB online. Retrieved 2009-04-26. 66. ^ Even-Zohar, C. (1999-11-03). "De Beers to Halve Diamond Stockpile". National Jeweler. Retrieved 2009-04-26. 67. ^ "Judgment of the Court of First Instance of 11 July 2007 – Alrosa v Commission". EUR-Lex. 2007. Retrieved 2009-04-26. 68. ^ "Mining operations". The De Beers Group. Retrieved 2011-01-04. 69. ^ "Diamond producer Alrosa to resume market diamond sales in May". RIA Novosti. 2009-05-06. Retrieved 2009-05-25. 70. ^ "Media releases - Media Centre - Alrosa". Alrosa. 2009-12-22. Retrieved 2011- 01-04. 71. ^ "Another record profit for BHP". ABC News. 2007-08-22. Retrieved 2007-08- 23. 72. ^ "Our Companies". Rio Tinto web site. Rio Tinto. Retrieved 2009-03-05. 73. ^ a b c Broadman, H. G.; Isik, G (2007). Africa's silk road. World Bank Publications. pp. 297–299. ISBN 0-8213-6835-4. 74. ^ "Bourse listing". World Federation of Diamond Bourses. Retrieved 2007-04-04. 75. ^ "North America Diamond Sales Show No Sign of Slowing". A&W diamonds. Retrieved 2009-05-05. 76. ^ http://www.diamonds.net/news/NewsItem.aspx?ArticleID=33243 77. ^ a b http://www.jckonline.com/2011/01/26/10-things-rocking-industry 78. ^ http://www.jckonline.com/blogs/cutting-remarks/2011/01/14/interview- forevermark-ceo 79. ^ George E. Harlow (1998). The nature of diamonds. Cambridge University Press. p. 34. ISBN 0-521-62935-7. 80. ^ Jessica Elzea Kogel (2006). Industrial minerals & rocks. Society for Mining, Metallurgy, and Exploration (U.S.). p. 416. ISBN 0-87335-233-5. 81. ^ "The Australian Diamond Industry". Retrieved 2009-08-04. 82. ^ Erlich, Edward and Dan Hausel, W. (2002). Diamond deposits: origin, exploration, and history of discovery. SME. p. 158. ISBN 0-87335-213-0. 83. ^ a b James, Duncan S (1998). Antique jewellery: its manufacture, materials and design. Osprey Publishing. pp. 82–102. ISBN 0-7478-0385-4. 84. ^ Prelas, Mark Antonio; Popovici, Galina; Bigelow, Louis K. (1998). Handbook of industrial diamonds and diamond films. CRC Press. pp. 984–992. ISBN 0-8247-9994- 1. 85. ^ Popular Mechanics. 74. Hearst Magazines. 1940. pp. 760–764. ISSN 0032- 4558. 86. ^ a b Spear, K.E; Dismukes, J.P. (1994). Synthetic Diamond: Emerging CVD Science and Technology. Wiley–IEEE. p. 628. ISBN 0-471-53589-3. 87. ^ Holtzapffel, C. (1856). Turning And Mechanical Manipulation. Holtzapffel & Co. pp. 176–178. ISBN 1-879335-39-5. 88. ^ Coelho, R.T.; Yamada, S.; Aspinwall, D.K.; Wise, M.L.H. (1995). "The application of polycrystalline diamond (PCD) tool materials when drilling and reaming aluminum-based alloys including MMC". International Journal of Machine Tools and Manufacture 35 (5): 761–774. doi:10.1016/0890-6955(95)93044-7. 89. ^ Sakamoto, M.; Endriz, J.G.; Scifres, D.R. (1992). "120 W CW output power from monolithic AlGaAs (800 nm) laser diode array mounted on diamond heatsink". Electronics Letters 28 (2): 197–199. doi:10.1049/el:19920123. 90. ^ Shigley, J.E. (2002). "Gemesis Laboratory Created Diamonds". Gems & Gemology 38 (4): 301–309. 91. ^ Shigley, J.E. (2004). "Lab Grown Colored Diamonds from Chatham Created Gems". Gems & Gemology 40 (2): 128–145. 92. ^ Werner, M.; Locher, R (1998). "Growth and application of undoped and doped diamond films". Reports on Progress in Physics 61: 1665. doi:10.1088/0034- 4885/61/12/002. 93. ^ Kogel, J. E. (2006). Industrial Minerals & Rocks. SME. pp. 426–430. ISBN 0- 87335-233-5. 94. ^ O'Donoghue, M.; Joyner, L. (2003). Identification of gemstones. Great Britain: Butterworth-Heinemann. pp. 12–19. ISBN 0-7506-5512-7. 95. ^ Barnard, A. S (2000). The diamond formula. Butterworth-Heinemann. p. 115. ISBN 0-7506-4244-0. 96. ^ Shigley, J.E. (2007). "Observations on new coated gemstones". Gemmologie: Zeitschrift der Deutschen Gemmologischen Gesellschaft 56 (1–2): 53–56. 97. ^ J. F. Wenckus "Method and means of rapidly distinguishing a simulated diamond from natural diamond" U.S. Patent 4,488,821 December 18, 1984 98. ^ a b Edwards, H. G. M. and Chalmers, G. M (2005). Raman spectroscopy in archaeology and art history. Royal Society of Chemistry. pp. 387–394. ISBN 0-85404- 522-8. 99. ^ a b Welbourn, C. (2006). "Identification of Synthetic Diamonds: Present Status and Future Developments". Gems and Gemology 42 (3): 34–35. 100. ^ Donahue, P.J. (2004-04-19). "DTC Appoints GIA Distributor of DiamondSure and DiamondView". Professional Jeweler Magazine. Retrieved 2009-03-02. 101. ^ "SSEF diamond spotter and SSEF illuminator". SSEF Swiss Gemmological Institute. Retrieved 2009-05-05. Books • C. Even-Zohar (2007). From Mine to Mistress: Corporate Strategies and Government Policies in the International Diamond Industry (2nd ed.). Mining Journal Press. • G. Davies (1994). Properties and growth of diamond. INSPEC. ISBN 0-85296-875-2. • M. O'Donoghue, M (2006). Gems. Elsevier. ISBN 0-7506-5856-8. • M. O'Donoghue and L. Joyner (2003). Identification of gemstones. Great Britain: Butterworth-Heinemann. ISBN 0-7506-5512-7. • A. Feldman and L.H. Robins (1991). Applications of Diamond Films and Related Materials. Elsevier. • J.E. Field (1979). The Properties of Diamond. London: Academic Press. ISBN 0-12- 255350-0. • J.E. Field (1992). The Properties of Natural and Synthetic Diamond. London: Academic Press. ISBN 0-12-255352-7. • W. Hershey (1940). The Book of Diamonds. Hearthside Press New York. ISBN 1-4179- 7715-9. • S. Koizumi, C.E. Nebel and M. Nesladek (2008). Physics and Applications of CVD Diamond. Wiley VCH. ISBN 3-527-40801-0. • L.S. Pan and D.R. Kani (1995). Diamond: Electronic Properties and Applications. Kluwer Academic Publishers. ISBN 0-7923-9524-7. • Pagel-Theisen, Verena (2001). Diamond Grading ABC: the Manual. Antwerp: Rubin & Son. ISBN 3-9800434-6-0. • R.L. Radovic, P.M. Walker and P.A. Thrower (1965). Chemistry and physics of carbon: a series of advances. New York: Marcel Dekker. ISBN 0-8247-0987-X. • M. Tolkowsky (1919). Diamond Design: A Study of the Reflection and Refraction of Light in a Diamond. London: E. & F.N. Spon. • R.W. Wise (2003). Secrets Of The Gem Trade, The Connoisseur's Guide To Precious Gemstones. Brunswick House Press. • A.M. Zaitsev (2001). Optical Properties of Diamond: A Data Handbook. Springer. ISBN 3-540-66582-X. External links

Wikimedia Commons has media related to: Diamond

Look up diamond in Wiktionary, the free dictionary.

• Properties of diamond: Ioffe database • Interactive structure of bulk diamond (Java applet) • Epstein, Edward Jay (1982). The diamond invention (Complete book, includes "Chapter 20: Have you ever tried to sell a diamond?") • "A Contribution to the Understanding of Blue Fluorescence on the Appearance of Diamonds". (2007) Gemological Institute of America (GIA) • Tyson, Peter (November 2000). "Diamonds in the Sky". Retrieved March 10, 2005.

Telescope From Wikipedia, the free encyclopedia

For other uses, see Telescope (disambiguation).

The 100 inch (2.5 m) Hooker reflecting telescope at Mount Wilson Observatory near Los Angeles, California.

A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation (such as visible light). The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s (the 17th century), using glass lenses. They found use in terrestrial applications and astronomy. Within a few decades, the reflecting telescope was invented, which used mirrors. In the 20th century many new types of telescopes were invented, including radio telescopes in the 1930s and infrared telescopes in the 1960s. The word telescope now refers to a wide range of instruments detecting different regions of the electromagnetic spectrum, and in some cases other types of detectors. A major offshoot development of the telescope is the microscope, for magnifying small things. Classical telescopes are an optical computer that form an image by replicating a Fourier transform in real-time using the same medium collected for processing and display output. The word "telescope" (from the Greek τ ῆ λε , tele "far" and σκοπε ῖ ν , skopein "to look or see"; τηλεσκόπος, teleskopos "far-seeing") was coined in 1611 by the Greek mathematician Giovanni Demisiani for one of Galileo Galilei's instruments presented at a banquet at the Accademia dei Lincei.[1][2][3] In the Starry Messenger Galileo had used the term "perspicillum". Contents [hide]

• 1 History • 2 Types of telescopes o 2.1 Optical telescopes o 2.2 Radio telescopes o 2.3 X-ray telescopes o 2.4 Gamma-ray telescopes o 2.5 High energy particle telescopes o 2.6 Other types of telescopes • 3 Types of telescope mount • 4 Atmospheric electromagnetic opacity • 5 Telescopic image from different telescope types • 6 Telescopes by spectrum • 7 Lists of telescopes • 8 See also • 9 References • 10 Further reading • 11 External links [edit] History Main article: History of the telescope

The earliest evidence of working telescopes were the refracting telescopes that appeared in the Netherlands in 1608. Their development is credited to three individuals: Hans Lippershey and Zacharias Janssen, who were spectacle makers in Middelburg, and Jacob Metius of Alkmaar.[4] Galileo greatly improved upon these designs the following year. The idea that the objective, or light-gathering element, could be a mirror instead of a lens was being investigated soon after the invention of the refracting telescope.[5] The potential advantages of using parabolic mirrors—reduction of spherical aberration and no chromatic aberration—led to many proposed designs and several attempts to build reflecting telescopes.[6] In 1668, Isaac Newton built the first practical reflecting telescope, which bears his name, the Newtonian reflector. The invention of the achromatic lens in 1733 partially corrected color aberrations present in the simple lens and enabled the construction of shorter, more functional refracting telescopes. Reflecting telescopes, though not limited by the color problems seen in refractors, were hampered by the use of fast tarnishing speculum metal mirrors employed during the 18th and early 19th century—a problem alleviated by the introduction of silver coated glass mirrors in 1857,[7] and aluminized mirrors in 1932.[8] The maximum physical size limit for refracting telescopes is about 1 meter (40 inches), dictating that the vast majority of large optical researching telescopes built since the turn of the 20th century have been reflectors. The largest reflecting telescopes currently have objectives larger than 10 m (33 feet). The 20th century also saw the development of telescopes that worked in a wide range of wavelengths from radio to gamma-rays. The first purpose built radio telescope went into operation in 1937. Since then, a tremendous variety of complex astronomical instruments have been developed. [edit] Types of telescopes This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (July 2008)

The name "telescope" covers a wide range of instruments. Telescopes may be classified by the type of radiation they detect. Most detect electromagnetic radiation, but there are major differences in how astronomers must go about collecting light (electromagnetic radiation) in different frequency bands. Telescopes may also be classified by location: ground telescope, space telescope, or flying telescope. They may also be classified by whether they are operated by professional astronomers or amateur astronomers. A vehicle or permanent campus containing one or more telescopes or other instruments is called an observatory. [edit] Optical telescopes

50 cm refracting telescope at Nice Observatory.

Main article: Optical telescope An optical telescope gathers and focuses light mainly from the visible part of the electromagnetic spectrum (although some work in the infrared and ultraviolet).[9] Optical telescopes increase the apparent angular size of distant objects as well as their apparent brightness. In order for the image to be observed, photographed, studied, and sent to a computer, telescopes work by employing one or more curved optical elements—usually made from glass—lenses, and/or mirrors to gather light and other electromagnetic radiation to bring that light or radiation to a focal point. Optical telescopes are used for astronomy and in many non-astronomical instruments, including: theodolites (including transits), spotting scopes, monoculars, binoculars, camera lenses, and spyglasses. There are three main optical types: • The refracting telescope which uses lenses to form an image. • The reflecting telescope which uses an arrangement of mirrors to form an image. • The catadioptric telescope which uses mirrors combined with lenses to form an image. Beyond these basic optical types there are many sub-types of varying optical design classified by the task they perform such as Astrographs, Comet seekers, Solar telescope, etc. Telescopes may also be classified by the wavelengths of light they work with: • Ultraviolet telescope, shorter wavelengths than visible light • X-ray telescope , shorter wavelengths than ultraviolet light • Infrared telescope , longer wavelengths than visible light • Submillimetre telescopes , longer wavelengths than infrared light Light Comparison Frequency Photon Energy Name Wavelength (Hz) (eV) Gamma less than 0.01 more than 10 100 keV - 300+ X ray nm EHZ GeV 30 PHz - 30 120 eV to 120 X-Ray 0.01 to 10 nm X EHZ keV Ultraviole 10 nm - 400 30 EHZ - 790 3 eV to 124 eV t nm THz 390 nm - 750 790 THz - 405 Visible 1.7 eV - 3.3 eV X nm THz 750 nm - 1 405 THz - 300 1.24 meV - 1.7 Infrared X mm GHz eV Microwav 1 mm - 1 300 GHz - 300 1.24 meV - 1.24 e meter MHz µeV 1.24 meV - 12.4 Radio 1 mm - km 300 GHz - 3 Hz X feV

As wavelengths become longer, it becomes easier to use antenna technology to interact with electromagnetic radiation (although it is possible to make very tiny antenna). The near-infrared can be handled much like visible light, however in the far-infrared and submillimetre range, telescopes can operate more like a radio telescope. For example the James Clerk Maxwell Telescope observes from wavelengths from 3 μm (0.003 mm) to 2000 μm (2 mm), but uses a parabolic aluminum antenna.[10] On the other hand, the Spitzer Space Telescope, observing from about 3 μm (0.003 mm) to 180 μm (0.18 mm) uses a mirror (reflecting optics). Also using reflecting optics, the Hubble Space Telescope with Wide Field Camera 3 can observe from about 0.2 μm (0.0002 mm) to 1.7 μm (0.0017 mm) (from ultra-violet to infrared light).[11] • Fresnel Imager , an optical lens technology • X-ray optics , optics for certain x-ray wavelengths Another threshold in telescope design, as photon energy increases (shorter wavelengths and higher frequency) is the use of fully reflecting optics rather then glancing-incident optics. Telescopes such as TRACE and SOHO use special mirrors to reflect Extreme ultraviolet, producing higher resolution and brighter images then otherwise possible. A larger aperture does not just mean more light is collected, it is collected at a higher diffraction limit. [edit] Radio telescopes

The Very Large Array at Socorro, New Mexico, United States.

Main article: Radio telescope

Radio telescopes are directional radio antennas used for radio astronomy. The dishes are sometimes constructed of a conductive wire mesh whose openings are smaller than the wavelength being observed. Multi-element Radio telescopes are constructed from pairs or larger groups of these dishes to synthesize large 'virtual' apertures that are similar in size to the separation between the telescopes; this process is known as aperture synthesis. As of 2005, the current record array size is many times the width of the Earth—utilizing space-based Very Long Baseline Interferometry (VLBI) telescopes such as the Japanese HALCA (Highly Advanced Laboratory for Communications and Astronomy) VSOP (VLBI Space Observatory Program) satellite. Aperture synthesis is now also being applied to optical telescopes using optical interferometers (arrays of optical telescopes) and aperture masking interferometry at single reflecting telescopes. Radio telescopes are also used to collect microwave radiation, which is used to collect radiation when any visible light is obstructed or faint, such as from quasars. Some radio telescopes are used by programs such as SETI and the Arecibo Observatory to search for extraterrestrial life. [edit] X-ray telescopes

Einstein Observatory was a space-based focusing optical X-ray telescope from 1978. [12] Main article: X-ray telescope

X-ray telescopes can use X-ray optics, such as a Wolter telescopes composed of ring-shaped 'glancing' mirrors made of heavy metals that are able to reflect the rays just a few degrees. The mirrors are usually a section of a rotated parabola and a hyperbola, or ellipse. In 1952, Hans Wolter outlined 3 ways a telescope could be built using only this kind of mirror.[13][14] Examples of an observatory using this type of telescope are the Einstein Observatory, ROSAT, and the Chandra X-Ray Observatory. By 2010, Wolter focusing X-ray telescopes are possible up to 79 keV.[12] [edit] Gamma-ray telescopes Higher energy X-ray and Gamma-ray telescopes refrain from focusing completely and use coded aperture masks: the patterns of the shadow the mask creates can be reconstructed to form an image. X-ray and Gamma-ray telescopes are usually on Earth-orbiting satellites or high-flying balloons since the Earth's atmosphere is opaque to this part of the electromagnetic spectrum. However, high energy x-rays and gamma-rays do not form an image in the same way as telescopes at visible wavelengths. An example of this type of telescope is the Fermi Gamma-ray Space Telescope. The detection of very high energy gamma rays, with shorter wavelength and higher frequency than regular gamma rays, requires further specialization. An example of this type of observatory is VERITAS. Very high energy gamma-rays are still photons, like visible light, whereas cosmic- rays includes particles like electrons, protons, and heavier nuclei. [edit] High energy particle telescopes High-energy astronomy requires specialized telescopes to make observations since most of these particles go through most metals and glasses. In other types of high energy particle telescopes there is no image-forming optical system. Cosmic-ray telescopes usually consist of an array of different detector types spread out over a large area. A Neutrino telescope consists of a large mass of water or ice, surrounded by an array of sensitive light detectors known as photomultiplier tubes. Energetic neutral atom observatories like Interstellar Boundary Explorer detect particles traveling at certain energies. [edit] Other types of telescopes • Gravitational wave detector , aka gravitational wave telescope • Neutrino detector , aka neutrino telescope [edit] Types of telescope mount Main article: Telescope mount

A telescope mount is a mechanical structure which supports a telescope. Telescope mounts are designed to support the mass of the telescope and allow for accurate pointing of the instrument. Many sorts of mounts have been developed over the years, with the majority of effort being put into systems that can track the motion of the stars as the Earth rotates. The two main types of tracking mount are: • Altazimuth mount • Equatorial mount [edit] Atmospheric electromagnetic opacity See also: Airmass

Since the atmosphere is opaque for most of the electro-magnetic spectrum, only a few bands can be observed from the Earth's surface. These bands are visible – near-infrared and a portion of the radio-wave part of the spectrum. For this reason there are no X-ray or far-infrared ground-based telescopes as these have to be flown in space to observe. Even if a wavelength is observable from the ground, it might still be advantageous to fly it on a satellite due to astronomical seeing.

A diagram of the electromagnetic spectrum with the Earth's atmospheric transmittance (or opacity) and the types of telescopes used to image parts of the spectrum. [edit] Telescopic image from different telescope types Different types of telescope, operating in different wavelength bands, provide different information about the same object. Together they provide a more comprehensive understanding. A 6′ wide view of the Crab nebula supernova remnant, viewed at different wavelengths of light by various telescopes [edit] Telescopes by spectrum Telescopes that operate in the electromagnetic spectrum: Name Telescope Astronomy Wavelength

Radio astronomy more than Radio Radio telescope (Radar astronomy) 1 mm

Submillime Submillimetre Submillimetre 0.1 mm - tre telescopes* astronomy 1 mm

Far-infrared 30 µm - Far Infrared – astronomy 450 µm

700 nm - Infrared Infrared telescope Infrared astronomy 1 mm

Visible Visible spectrum Visible-light 400 nm - telescopes astronomy 700 nm

Ultraviolet 10 nm - Ultraviolet Ultraviolet telescopes* astronomy 400 nm

0.01 nm - X-ray X-ray telescope X-ray astronomy 10 nm

Gamma-ray less than Gamma-ray – astronomy 0.01 nm

*Links to categories. [edit] Lists of telescopes • List of optical • Category:Telescopes telescopes • Category:Cosmic-ray • List of largest optical telescopes reflecting telescopes • Category:Gamma-ray • List of largest optical telescopes refracting telescopes • Category:Gravitation • List of largest optical al wave telescopes telescopes • Category:High historically energy particle • List of radio telescopes telescopes • Category:Infrared • List of solar telescopes telescopes • Category:Submillimet • List of space re telescopes telescopes • Category:Ultraviolet • List of telescope telescopes parts and • Category:X-ray construction telescopes • List of telescope types

[edit] See also • Airmass • Amateur telescope making • Angular resolution • Aperture synthesis • ASCOM open standards for computer control of telescopes • Bahtinov mask • Carey mask • Dynameter • f-number • First light • GoTo telescope • Hartmann mask • Keyhole problem • Microscope • Remote Telescope Markup Language • Robotic telescope • Timeline of telescope technology • Timeline of telescopes, observatories, and observing technology [edit] References 1. ^ archive.org " Galileo His Life And Work " BY J. J. FAHIE " Galileo usually called the telescope occhicde or cannocchiale ; and now he calls the microscope occhialino. The name telescope was first suggested by Demisiani in 1612 " 2. ^ Sobel (2000, p.43), Drake (1978, p.196) 3. ^ Rosen, Edward, The Naming of the Telescope (1947) 4. ^ galileo.rice.edu The Galileo Project > Science > The Telescope by Al Van Helden "The Hague discussed the patent applications first of Hans Lipperhey of Middelburg, and then of Jacob Metius of Alkmaar... another citizen of Middelburg, Sacharias Janssen had a telescope at about the same time but was at the Frankfurt Fair where he tried to sell it" 5. ^ Stargazer - By Fred Watson, Inc NetLibrary, Page 109 6. ^ Attempts by Niccolò Zucchi and James Gregory and theoretical designs by Bonaventura Cavalieri, Marin Mersenne, and Gregory among others 7. ^ madehow.com - Inventor Biographies - Jean-Bernard-Léon Foucault Biography (1819-1868) 8. ^ Bakich sample pages Chapter 2, Page 3 "John Donavan Strong, a young physicist at the California Institute of Technology, was one of the first to coat a mirror with aluminum. He did it by thermal vacuum evaporation. The first mirror he aluminized, in 1932, is the earliest known example of a telescope mirror coated by this technique." 9. ^ Barrie William Jones, The search for life continued: planets around other stars, page 111 10. ^ The James-Clerk-Maxwell Observatory: The largest submillimetre radio telescope in the world 11. ^ ESA/Hubble - Hubble's Instruments: WFC3 - Wide Field Camera 3 12. ^ a b NuStar: Instrumentation: Optics 13. ^ Wolter, H. (1952), "Glancing Incidence Mirror Systems as Imaging Optics for X-rays", Ann. Physik 10: 94. 14. ^ Wolter, H. (1952), "A Generalized Schwarschild Mirror Systems For Use at Glancing Incidence for X-ray Imaging", Ann. Physik 10: 286. [edit] Further reading Overhead projector From Wikipedia, the free encyclopedia

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (February 2008)

Overhead projector in operation during a classroom lesson An overhead projector is a variant of slide projector that is used to display images to an audience. Contents [hide]

• 1 Mechanism o 1.1 Focal-length adjustment o 1.2 Illumination • 2 History o 2.1 Use in education o 2.2 LCD overhead displays • 3 Decline in use • 4 See also • 5 References [edit] Mechanism An overhead projector typically consists of a large box containing a very bright lamp and a fan to cool it. On top of the box is a large fresnel lens that collimates the light. Above the box, typically on a long arm, is a mirror and lens that focusses and redirects the light forward instead of up. Transparencies are placed on top of the lens for display. The light from the lamp travels through the transparency and into the mirror where it is shone forward onto a screen for display. The mirror allows both the presenter and the audience to see the image at the same time, the presenter looking down at the transparency as if writing, the audience looking forward at the screen. The height of the mirror can be adjusted, to both focus the image and to make the image larger or smaller depending on how close the projector is to the screen. [edit] Focal-length adjustment Better-quality overhead projectors offer an adjustment wheel or screw on the body of the projector, to move the lamp towards or away from the fresnel lens. When the mirror above the lens is moved too high or too low, it moves out of the best focal distance for an evenly white image, resulting in a projected image with either blue or brown color fringing around the outside edge of the screen. Turning the adjustment wheel moves the lamp to correct the focal distance and restores the all-white projected image. [edit] Illumination The lamp technology of an overhead projector is typically very simple compared to a modern LCD or DLP video projector. Most overheads use an extremely high-power halogen lamp that may consume up to 750 watts yet produces a fairly dim, yellowed image. A high-flow blower is required to keep the bulb from melting itself due to the heat output. Further, the intense heat usually causes the halogen lamp to fail quickly, often lasting less than 100 hours before failing and requiring replacement. A modern LCD or DLP uses an arc lamp which has a higher luminous efficacy and lasts for thousands of hours. A negative to LCD/DLP technology is the warm up time required for arc lamps. Older overhead projectors used a tubular quartz lamp body containing the filament only, which mounted above a bowl-shaped polished reflector. However because the lamp was suspended above and outside the reflector, a large amount of light was cast to the sides inside the projector body that was wasted and required a very large lamp for sufficient screen illumination. More recent projectors use an integrated lamp and conical reflector assembly that allows the lamp to be located deep within the reflector so that more light is focused towards the fresnel lens, allowing for a lower-power lamp. The most recent innovation for overhead projectors with integrated lamps/reflectors is the quick- swap dual-lamp control, allowing two lamps to be installed in the projector in movable sockets. If one lamp fails during a presentation, the presenter can merely move a lever to slide the spare into position and continue with the presentation, without needing to open the projection unit or waiting for the failed bulb to cool before replacing it. [edit] History The first overhead projector was used for police identification work. It used a cellophane roll over a 9-inch stage allowing facial characteristics to be rolled across the stage. The U.S. Army in 1945 was the first to use it in quantity for training as World War II wound down. It began to be widely used in schools and businesses in the late 1950s and early 1960s. A major manufacturer of overhead projectors in this early period was the company 3M. As the demand for projectors grew, Buhl Industries was founded in 1953, and became the leading US contributor for several optical refinements for the overhead projector and its projection lens. In 1957, the United States' first Federal Aid to Education program stimulated overhead sales which remained high up to the late 1990s and into the 21st Century. [edit] Use in education This section does not cite any references or sources. Please help improve this section by adding citations to reliable sources. Unsourced material may be challenged and removed. (March 2010)

The overhead projector facilitates an easy low-cost interactive environment for educators. Teaching materials can be pre-printed on plastic sheets, upon which the educator can directly write using a non-permanent, washable color marking pen. This saves time, since the transparency can be pre-printed and used repetitively, rather than having materials written manually before each class. The overhead is typically placed at a comfortable writing height for the educator and allows the educator to face the class, facilitating better communication between the students and teacher. The enlarging features of the projector allow the educator to write in a comfortable small script in a natural writing position rather than writing in an overly large script on a blackboard and having to constantly hold his arm out in midair to write on the blackboard. When the transparency sheet is full of written or drawn material, it can simply be replaced with a new, fresh sheet with more pre-printed material, again saving class time vs a blackboard that would need to be erased and teaching materials rewritten by the educator. Following the class period, the transparencies are easily restored to their original unused state by washing off with soap and water. [edit] LCD overhead displays In the early 1980s–1990s, overhead projectors were used as part of a classroom computer display/projection system. A liquid-crystal panel mounted in a plastic frame was placed on top of the overhead projector and connected to the video output of the computer, often splitting off the normal monitor output. A cooling fan in the frame of the LCD panel would blow cooling air across the LCD to prevent overheating that would fog the image. The first of these LCD panels were monochrome-only, and could display NTSC video output such as from an Apple II computer or VCR. In the late 1980s color models became available, capable of "thousands" of colors (16-bit color), for the color Macintosh and VGA PCs. The displays were never particularly fast to refresh or update, resulting in the smearing of fast- moving images, but it was acceptable when nothing else was available. The Do-It-Yourself community has started using this idea to make low-cost home theater projectors. By removing the casing and backlight assembly of a common LCD monitor, one can use the exposed LCD screen in conjunction with the overhead projector to project the contents of the LCD screen to the wall at a much lower cost than with standard LCD projectors. Due to the mirroring of the image in the head of the overhead projector, the image on the wall is "re- flipped" to where it would be if one was looking at the LCD screen normally. [edit] Decline in use Overhead projectors were once a common fixture in most classrooms and business conference rooms, but today are slowly being replaced by document cameras, dedicated computer projection systems and interactive whiteboards.[citation needed] Such systems allow users to make animated, interactive presentations with movement and video, typically using software like Microsoft PowerPoint. The primary reason for this gradual replacement is the deeply ingrained use of computing technology in modern society and the inability of overheads to easily support the features that modern users demand. While an overhead can display static images fairly well, it performs poorly at displaying moving images. The LCD video display panels that were once used have fallen out of favor due to the limited resolution available and relatively dim, fuzzy image produced by the overhead. The standards of users have also increased, so that a dim, fuzzy overhead projection that is too bright in the center and too dim around the edges is no longer acceptable. The optical focus, linearity, brightness and clarity of an overhead generally cannot match that of a video projector primarily due to the plastic fresnel lens, which can only approximate what would normally be an extremely large and heavy glass lens. Video projectors utilize extremely small picture generation mechanisms, allowing for precision optics that far exceed the plastic fresnel lens' optical performance. They also include additional optics that eliminate the hotspot in the center of the screen directly above the light source, so that the brightness is uniform everywhere on the projection screen. Critics feel that there are some downsides as these technologies are more prone to failure and have a much steeper learning curve for the user than a standard overhead projector. While a computer projection system eliminates the need to create hard copy transparencies (which can be quite expensive, particularly if made in color) of the slide show presentation, many presenters make both in case the computer hardware fails. Furthermore, the overhead projector allows a more direct interaction through live writing on the transparency. [edit] See also • Opaque projector , a related type of the projector • Projector (disambiguation) • Slide projector • Slideshow • Transparency (projection) [edit] References