A mirror is an object that reflects light in such a way that, for incident light in some range of wavelengths, the reflected light preserves many or most of the detailed physical characteristics of the original light, called specular reflection. This is different from other light-reflecting objects that do not preserve much of the original wave signal other than color and diffuse reflected light, such as flat-white paint.
The most familiar type of mirror is the plane mirror, which has a flat surface. Curved mirrors are also used, to produce magnified or diminished images or focus light or simply distort the reflected image.
Mirrors are commonly used for personal grooming or admiring oneself (where they are also called looking-glasses), for viewing the area behind and on the sides on motor vehicles while driving, for decoration, and architecture. Mirrors are also used in scientific apparatus such as telescopes and lasers, cameras, and industrial machinery. Most mirrors are designed for visible light; however, mirrors designed for other wavelengths of electromagnetic radiation are also used.
There are many types of glass mirrors, each representing a different manufacturing process and reflection type.
An aluminium glass mirror is made of a float glass manufactured using vacuum coating, i.e. aluminium powder is evaporated (or "sputtered") onto the exposed surface of the glass in a vacuum chamber and then coated with two or more layers of waterproof protective paint.
A low aluminium glass mirror is manufactured by coating silver and two layers of protective paint on the back surface of glass. A low aluminium glass mirror is very clear, light transmissive, smooth, and reflects accurate natural colors. This type of glass is widely used for framing presentations and exhibitions in which a precise color representation of the artwork is truly essential or when the background color of the frame is predominantly white.
A safety glass mirror is made by adhering a special protective film to the back surface of a silver glass mirror, which prevents injuries in case the mirror is broken. This kind of mirror is used for furniture, doors, glass walls, commercial shelves, or public areas.
A silkscreen printed glass mirror is produced using inorganic color ink that prints patterns through a special screen onto glass. Various colors, patterns, and glass shapes are available. Such a glass mirror is durable and more moisture resistant than ordinary printed glass and can serve for over 20 years. This type of glass is widely used for decorative purposes (e.g., on mirrors, table tops, doors, windows, kitchen chop boards, etc.).
A silver glass mirror is an ordinary mirror, coated on its back surface with silver, which produces images by reflection. This kind of glass mirror is produced by coating a silver, copper film and two or more layers of waterproof paint on the back surface of float glass, which perfectly resists acid and moisture. A silver glass mirror provides clear and actual images, is quite durable, and is widely used for furniture, bathroom and other decorative purposes.
Decorative glass mirrors are usually handcrafted. A variety of shades, shapes and glass thickness are often available.
A beam of light reflects off a mirror at an angle of reflection equal to its angle of incidence (if the size of a mirror is much larger than the wavelength of light). That is, if the beam of light is shining on a mirror's surface, at a ° angle vertically, then it reflects from the point of incidence at a ° angle, vertically in the opposite direction. This law mathematically follows from the interference of a plane wave on a flat boundary (of much larger size than the wavelength).
Objects viewed in a (plane) mirror will appear laterally inverted (e.g., if one raises one's right hand, the image's left hand will appear to go up in the mirror), but not vertically inverted (in the image a person's head still appears above their body). However, a mirror does not usually "swap" left and right any more than it swaps top and bottom. A mirror typically reverses the forward/backward axis. To be precise, it reverses the object in the direction perpendicular to the mirror surface (the normal). Because left and right are defined relative to front-back and top-bottom, the "flipping" of front and back results in the perception of a left-right reversal in the image. (If you stand side-on to a mirror, the mirror really does reverse your left and right, because that's the direction perpendicular to the mirror.)
Looking at an image of oneself with the front-back axis flipped results in the perception of an image with its left-right axis flipped. When reflected in the mirror, your right hand remains directly opposite your real right hand, but it is perceived as the left hand of your image. When a person looks into a mirror, the image is actually front-back reversed, which is an effect similar to the hollow-mask illusion. Notice that a mirror image is fundamentally different from the object and cannot be reproduced by simply rotating the object.
For things that may be considered as two-dimensional objects (like text), front-back reversal cannot usually explain the observed reversal. In the same way that text on a piece of paper appears reversed if held up to a light and viewed from behind, text held facing a mirror will appear reversed, because the observer is behind the text. Another way to understand the reversals observed in images of objects that are effectively two-dimensional is that the inversion of left and right in a mirror is due to the way human beings turn their bodies. To turn from viewing the side of the object facing the mirror to view the reflection in the mirror requires the observer to look in the opposite direction. To look in another direction, human beings turn their heads about a vertical axis. This causes a left-right reversal in the image but not an up-down reversal. If a person instead turns by bending over and looking at the mirror image between their legs, up-down will appear reversed but not left-right. This sort of reversal is simply a change relative to the observer and not a change intrinsic to the image itself, as with a three-dimensional object.
Left: Bronze mirror, New Kingdom of Egypt, Eighteenth Dynasty, 1540–1296 BC
Right: seated woman holding a mirror; Ancient Greek Attic red-figure lekythos by the Sabouroff Painter, c. 470–460 BC, National Archaeological Museum, Athens, Greece
The first mirrors used by humans were most likely pools of dark, still water, or water collected in a primitive vessel of some sort. The requirements for making a good mirror are a surface with a very high degree of flatness (preferably but not necessarily with high reflectivity), and a surface roughness smaller than the wavelength of the light. The earliest manufactured mirrors were pieces of polished stone such as obsidian, a naturally occurring volcanic glass. Examples of obsidian mirrors found in Anatolia (modern-day Turkey) have been dated to around 6000 B.C. Mirrors of polished copper were crafted in Mesopotamia from 4000 B.C., and in ancient Egypt from around 3000 B.C. Polished stone mirrors from Central and South America date from around 2000 B.C. onwards. In China, bronze mirrors were manufactured from around 2000 B.C., some of the earliest bronze and copper examples being produced by the Qijia culture. Mirrors made of other metal mixtures (alloys) such as copper and tin speculum metal may have also been produced in China and India. Mirrors of speculum metal or any precious metal were hard to produce and were only owned by the wealthy. These stone and metal mirrors could be made in very large sizes, but were difficult to polish and get perfectly flat; a process that became more difficult with increased size; so they often produced warped or blurred images. Stone mirrors often had poor reflectivity compared to metals, yet metals scratch or tarnish easily, so they frequently needed polishing. Depending upon the color, both often yielded reflections with poor color rendering. The poor image quality of ancient mirrors explains 1 Corinthians 13's reference to seeing "as in a mirror, darkly."
In her history of the mirror, Sabine Melchior-Bonnet draws significant attention to the relation of the mirror to Greek philosophy, specifically Socrates:
If well used, however, the mirror can aid moral meditation between man and himself. Socrates, we are told by Diogenes, urged young people to look at themselves in mirrors so that, if they were beautiful, they would become worthy of their beauty, and if they were ugly, they would know how to hide their disgrace through learning. The mirror, a tool by which to "know thyself," invited man to not mistake himself for God, to avoid pride by knowing his limits, and to improve himself. His was thus not a passive mirror of imitation but an active mirror of transformation. (p.106)
Glass was a desirable material for mirrors. Because the surface of glass is naturally smooth, it produces reflections with very little blur. In addition, glass is very hard and scratch-resistant. However, glass by itself has little reflectivity, so people began coating it with metals to increase the reflectivity. Metal-coated glass mirrors are said by the Roman scholar Pliny the Elder to have been invented in Sidon (modern-day Lebanon) in the first century A.D., although no archeological evidence of them date from before the third century. According to Pliny, the people of Sidon developed a technique for creating crude mirrors by coating blown glass with molten lead. Glass mirrors backed with gold leaf are mentioned by Pliny in his Natural History, written in about 77 A.D. Because there were few ways to make a smooth piece of glass with a uniform thickness, these ancient glass-mirrors were made by blowing a glass bubble, and then cutting off a small, circular section, producing mirrors that were either concave or convex. These circular mirrors were typically small, from five to eight inches (13–20 cm) in diameter. These small mirrors produced distorted images, yet were prized objects of high value. These ancient glass mirrors were very thin, thus very fragile, because the glass needed to be extremely thin to prevent cracking when coated with a hot, molten metal. Due to the poor quality, high cost, and small size of these ancient glass mirrors, solid metal-mirrors primarily of steel were usually preferred until the late nineteenth century.
Parabolic mirrors were described and studied in classical antiquity by the mathematician Diocles in his work On Burning Mirrors. Ptolemy conducted a number of experiments with curved polished iron mirrors, and discussed plane, convex spherical, and concave spherical mirrors in his Optics. Parabolic mirrors were also described by the physicist Ibn Sahl in the tenth century, and Ibn al-Haytham discussed concave and convex mirrors in both cylindrical and spherical geometries, carried out a number of experiments with mirrors, and solved the problem of finding the point on a convex mirror at which a ray coming from one point is reflected to another point. By the 11th century, glass mirrors were being produced in Moorish Spain.
In China, people began making mirrors by coating metallic objects with silver-mercury amalgams as early as 500 A.D. This was accomplished by coating the mirror with the amalgam, and then heating it until the mercury boiled away, leaving only the silver behind.
The problems of making metal-coated, glass mirrors was due to the difficulties in making glass that was very clear, as most ancient glass was tinted green with iron. This was overcome when people began mixing soda, limestone, potash, manganese, and fern ashes with the glass. There was also no way for the ancients to make flat panes of glass with uniform thicknesses. The earliest methods for producing glass panes began in France, when people began blowing glass bubbles, and then spinning them rapidly to flatten them out into plates from which pieces could be cut. However, these pieces were still not uniform in thickness, so produced distorted images as well. A better method was to blow a cylinder of glass, cut off the ends, slice it down the center, and unroll it onto a flat hearth. This method produced the first mirror-quality glass panes, but it was very difficult and resulted in a lot of breakage. Even windows were primarily made of oiled paper or stained glass, until the mid-nineteenth century, due to the high cost of making clear, flat panes of glass.
The method of making flat panes of clear glass from blown cylinders began in Germany and evolved through the Middle Ages, until being perfected by the Venetians in the sixteenth century. The Venetians began using lead glass for its crystal-clarity and its easier workability. Some time during the early Renaissance, European manufacturers perfected a superior method of coating glass with a tin-mercury amalgam, producing an amorphous coating with better reflectivity than crystalline metals and causing little thermal shock to the glass. The exact date and location of the discovery is unknown, but in the sixteenth century, Venice, a city famed for its glass-making expertise, became a center of mirror production using this new technique. Glass mirrors from this period were extremely expensive luxuries. For example, in the late seventeenth century, the Countess de Fiesque was reported to have traded an entire wheat farm for a mirror, considering it a bargain. These Venetian mirrors were limited in size to a maximum area of around 40 inches (100 cm) square, until modern glass panes began to be produced during the Industrial Revolution. The Saint-Gobain factory, founded by royal initiative in France, was an important manufacturer, and Bohemian and German glass, often rather cheaper, was also important.
The invention of the silvered-glass mirror is credited to German chemist Justus von Liebig in 1835. His process involved the deposition of a thin layer of metallic silver onto glass through the chemical reduction of silver nitrate. This silvering process was adapted for mass manufacturing and led to the greater availability of affordable mirrors. In the modern age, mirrors are often produced by the wet deposition of silver, or sometimes nickel or chromium (the latter used most often in automotive mirrors) via electroplating directly onto the glass substrate.
Vacuum deposition began with the study of the sputtering phenomenon during the 1920s and 1930s, which was a common problem in lighting in which metal ejected from the electrodes coated the glass, blocking output. However, turning sputtering into a reliable method of coating a mirror did not occur until the invention of semiconductors in the 1970s. Evaporation coating was pioneered by John Strong in 1912. Aluminum was a desirable material for mirrors, but was too dangerous to apply with electroplating. Strong used evaporation coating to make the first aluminum telescope mirrors in the 1930s. The first dielectric mirror was created in 1937 by Auwarter using evaporated rhodium, while the first metallic mirror to be enhanced with a dielectric coating of silicon dioxide was created by Hass the same year. In 1939 at the Schott Glass company, Walter Geffcken invented the first dielectric mirrors to use multilayer coatings (stacks).
Mirrors are manufactured by applying a reflective coating to a suitable substrate. The most common substrate is glass, due to its transparency, ease of fabrication, rigidity, hardness, and ability to take a smooth finish. The reflective coating is typically applied to the back surface of the glass, so that the reflecting side of the coating is protected from corrosion and accidental damage by the glass on one side and the coating itself and optional paint for further protection on the other.
In classical antiquity, mirrors were made of solid metal (bronze, later silver) and were too expensive for widespread use by common people; they were also prone to corrosion. Due to the low reflectivity of polished metal, these mirrors also gave a darker image than modern ones, making them unsuitable for indoor use with the artificial lighting of the time (candles or lanterns).
The method of making mirrors out of plate glass was invented by 13th-century Venetian glassmakers on the island of Murano, who covered the back of the glass with an amorphous coat of tin using a fire-gilding technique, obtaining near-perfect and undistorted reflection. For over one hundred years, Venetian mirrors installed in richly decorated frames served as luxury decorations for palaces throughout Europe, but the secret of the mercury process eventually arrived in London and Paris during the 17th century, due to industrial espionage. French workshops succeeded in large-scale industrialization of the process, eventually making mirrors affordable to the masses, although mercury's toxicity (a primary ingredient in gilding, which was boiled away forming noxious vapors) remained a problem.
The tin(II) chloride is applied because silver will not bond with the glass. The activator causes the tin/silver to harden. Copper is added for long-term durability. The paint protects the coating on the back of the mirror from scratches and other accidental damage.
In some applications, generally those that are cost-sensitive or that require great durability, such as for mounting in a prison cell, mirrors may be made from a single, bulk material such as polished metal. However, metals consist of small crystals (grains) separated by grain boundaries. Thus, crystalline metals do not reflect with perfect uniformity. Other methods like wet-deposition or electroplating produce a non-crystalline coating of amorphous metal (metallic glass). Lacking any grain boundaries, the amorphous coatings have higher reflectivity than crystalline metals of the same type. Electroplating must be performed by first coating the glass with carbon, to make the surface electrically conductive, thus the adhesion is often not as good as with wet-deposition. Both lack the ability to produce perfectly uniform thicknesses with high precision. When high precision or reflectivity is not a requirement, the coating may be placed on the back of the mirror so that the light passes through the glass, and the coating is the second surface it encounters. Therefore, these are called second-surface mirrors, which have the added benefit of high durability, because the glass substrate can protect the coating from damage.
For technical applications such as laser mirrors, the reflective coating is typically applied by vacuum deposition. Vacuum deposition provides an effective means of producing a very uniform coating, and controlling the thickness with high precision. In applications where great precision and low losses are required, the coated side of the mirror may be the first material encountered by the light, referred to as a first-surface mirror. This eliminates refraction and double reflections, also called "ghost reflections" (a weak reflection from the surface of the glass, and a stronger one from the reflecting metal), and reduces absorption of light by the mirror. Technical mirrors may use a silver, aluminium, or gold coating (the latter typically for infrared mirrors), and achieve reflectivities of 90–95% when new. A hard, protective, transparent overcoat may be applied to prevent oxidation of the reflective layer and scratching of the soft metal. Applications requiring higher reflectivity or greater durability, where wide bandwidth is not essential, use dielectric coatings, which can achieve reflectivities as high as 99.997% over a limited range of wavelengths. Because the coatings are usually transparent, absorption losses are negligible. Unlike with metals, the reflectivity of the individual dielectric-coatings is a function of Snell's law known as the Fresnel equations, determined by the difference in refractive index between layers. Therefore, the thickness and material of the coatings can be adjusted to be centered on any wavelength. Vacuum deposition can be achieved in a number of ways, including sputtering, evaporation deposition, arc deposition, reactive-gas deposition, and ion plating, among many others.
Mirrors can be manufactured to a wide range of engineering tolerances, including reflectivity, surface quality, surface roughness, or transmissivity, depending on the desired application. These tolerances can range from low, such as found in a normal household-mirror, to extremely high, like those used in lasers or telescopes. Increasing the tolerances allows better and more precise imaging or beam transmission over longer distances. In imaging systems this can help reduce anomalies (artifacts), distortion or blur, but at a much higher cost. Where viewing distances are relatively close or high precision is not a concern, lower tolerances can be used to make effective mirrors at affordable costs.
The reflectivity of a mirror is determined by the percentage of reflected light per the total of the incident light. The reflectivity may vary with wavelength. All or a portion of the light not reflected is absorbed by the mirror, while in some cases a portion may also transmit through. Although some small portion of the light will be absorbed by the coating, the reflectivity is usually higher for first-surface mirrors, eliminating both reflection and absorption losses from the substrate. The reflectivity is often determined by the type and thickness of the coating. When the thickness of the coating is sufficient to prevent transmission, all of the losses occur due to absorption. Aluminum is harder, less expensive, and more resistant to tarnishing than silver, and will reflect 85 to 90% of the light in the visible to near-ultraviolet range, but experiences a drop in its reflectance between 800 and 900 nm. Gold is very soft and easily scratched, costly, yet does not tarnish. Gold is greater than 96% reflective to near and far-infrared light between 800 and 12000 nm, but poorly reflects visible light with wavelengths shorter than 600 nm (yellow). Silver is expensive, soft, and quickly tarnishes, but has the highest reflectivity in the visual to near-infrared of any metal. Silver can reflect up to 98 or 99% of light to wavelengths as long as 2000 nm, but loses nearly all reflectivity at wavelengths shorter than 350 nm. Dielectric mirrors can reflect greater than 99.99% of light, but only for a narrow range of wavelengths, ranging from a bandwidth of only 10 nm to as wide as 100 nm for tunable lasers. However, dielectric coatings can also enhance the reflectivity of metallic coatings and protect them from scratching or tarnishing. Dielectric materials are typically very hard and relatively cheap, however the number of coats needed generally makes it an expensive process. In mirrors with low tolerances, the coating thickness may be reduced to save cost, and simply covered with paint to absorb transmission.
Surface quality, or surface accuracy, measures the deviations from a perfect, ideal surface shape. Increasing the surface quality reduces distortion, artifacts, and aberration in images, and helps increase coherence, collimation, and reduce unwanted divergence in beams. For plane mirrors, this is often described in terms of flatness, while other surface shapes are compared to an ideal shape. The surface quality is typically measured with items like interferometers or optical flats, and are usually measured in wavelengths of light (λ). These deviations can be much larger or much smaller than the surface roughness. A normal household-mirror made with float glass may have flatness tolerances as low as 9–14λ per inch (25.4 mm), equating to a deviation of 5600 through 8800 nanometers from perfect flatness. Precision ground and polished mirrors intended for lasers or telescopes may have tolerances as high as λ/50 (1/50 of the wavelength of the light, or around 12 nm) across the entire surface. The surface quality can be affected by factors such as temperature changes, internal stress in the substrate, or even bending effects that occur when combining materials with different coefficients of thermal expansion, similar to a bimetallic strip.
Surface roughness describes the texture of the surface, often in terms of the depth of the microscopic scratches left by the polishing operations. Surface roughness determines how much of the reflection is specular and how much diffuses, controlling how sharp or blurry the image will be.
For perfectly specular reflection, the surface roughness must be kept smaller than the wavelength of the light. Microwaves, which sometimes have a wavelength greater than an inch (~25 mm) can reflect specularly off a metal screen-door, continental ice-sheets, or desert sand, while visible light, having wavelengths of only a few hundred nanometers (a few hundred-thousandths of an inch), must meet a very smooth surface to produce specular reflection. For wavelengths that are approaching or are even shorter than the diameter of the atoms, such as X-rays, specular reflection can only be produced by surfaces that are at a grazing incidence from the rays.
Transmissivity is determined by the percentage of light transmitted per the incident light. Transmissivity is usually the same from both first and second surfaces. The combined transmitted and reflected light, subtracted from the incident light, measures the amount absorbed by both the coating and substrate. For transmissive mirrors, such as one-way mirrors, beam splitters, or laser output couplers, the transmissivity of the mirror is an important consideration. The transmissivity of metallic coatings are often determined by their thickness. For precision beam-splitters or output couplers, the thickness of the coating must be kept at very high tolerances to transmit the proper amount of light. For dielectric mirrors, the thickness of the coat must always be kept to high tolerances, but it is often more the number of individual coats that determine the transmissivity. For the substrate, the material used must also have good transmissivity to the chosen wavelengths. Glass is a suitable substrate for most visible-light applications, but other substrates such as zinc selenide or synthetic sapphire may be used for infrared or ultraviolet wavelengths.
Mirrors are commonly used as aids to personal grooming. They may range from small sizes, good to carry with oneself, to full body sized; they may be handheld, mobile, fixed or adjustable. A classic example of the latter is the cheval glass, which may be tilted.
With the sun as light source, a mirror can be used to signal by variations in the orientation of the mirror. The signal can be used over long distances, possibly up to 60 kilometres (37 mi) on a clear day. This technique was used by Native American tribes and numerous militaries to transmit information between distant outposts.
Microscopic mirrors are a core element of many of the largest high-definition televisions and video projectors. A common technology of this type is Texas Instruments' DLP. A DLP chip is a postage stamp-sized microchip whose surface is an array of millions of microscopic mirrors. The picture is created as the individual mirrors move to either reflect light toward the projection surface (pixel on), or toward a light absorbing surface (pixel off).
Other projection technologies involving mirrors include LCoS. Like a DLP chip, LCoS is a microchip of similar size, but rather than millions of individual mirrors, there is a single mirror that is actively shielded by a liquid crystal matrix with up to millions of pixels. The picture, formed as light, is either reflected toward the projection surface (pixel on), or absorbed by the activated LCD pixels (pixel off). LCoS-based televisions and projectors often use 3 chips, one for each primary color.
Large mirrors are used in rear projection televisions. Light (for example from a DLP as mentioned above) is "folded" by one or more mirrors so that the television set is compact.
Telescopes and other precision instruments use front silvered or first surface mirrors, where the reflecting surface is placed on the front (or first) surface of the glass (this eliminates reflection from glass surface ordinary back mirrors have). Some of them use silver, but most are aluminium, which is more reflective at short wavelengths than silver. All of these coatings are easily damaged and require special handling. They reflect 90% to 95% of the incident light when new. The coatings are typically applied by vacuum deposition. A protective overcoat is usually applied before the mirror is removed from the vacuum, because the coating otherwise begins to corrode as soon as it is exposed to oxygen and humidity in the air. Front silvered mirrors have to be resurfaced occasionally to keep their quality. There are optical mirrors such as mangin mirrors that are second surface mirrors (reflective coating on the rear surface) as part of their optical designs, usually to correct optical aberrations.
The reflectivity of the mirror coating can be measured using a reflectometer and for a particular metal it will be different for different wavelengths of light. This is exploited in some optical work to make cold mirrors and hot mirrors. A cold mirror is made by using a transparent substrate and choosing a coating material that is more reflective to visible light and more transmissive to infrared light.
A hot mirror is the opposite, the coating preferentially reflects infrared. Mirror surfaces are sometimes given thin film overcoatings both to retard degradation of the surface and to increase their reflectivity in parts of the spectrum where they will be used. For instance, aluminum mirrors are commonly coated with silicon dioxide or magnesium fluoride. The reflectivity as a function of wavelength depends on both the thickness of the coating and on how it is applied.
For scientific optical work, dielectric mirrors are often used. These are glass (or sometimes other material) substrates on which one or more layers of dielectric material are deposited, to form an optical coating. By careful choice of the type and thickness of the dielectric layers, the range of wavelengths and amount of light reflected from the mirror can be specified. The best mirrors of this type can reflect >99.999% of the light (in a narrow range of wavelengths) which is incident on the mirror. Such mirrors are often used in lasers.
Although most mirrors are designed to reflect visible light, surfaces reflecting other forms of electromagnetic radiation are also called "mirrors". The mirrors for other ranges of electromagnetic waves are used in optics and astronomy. Mirrors for radio waves (sometimes known as reflectors) are important elements of radio telescopes.
Two or more mirrors aligned exactly parallel and facing each other can give an infinite regress of reflections, called an infinity mirror effect. Some devices use this to generate multiple reflections:
It has been said that Archimedes used a large array of mirrors to burn Roman ships during an attack on Syracuse. This has never been proven or disproved; however, it has been put to the test. Recently, on a popular Discovery Channel show, MythBusters, a team from MIT tried to recreate the famous "Archimedes Death Ray". They were unsuccessful at starting a fire on the ship. Previous attempts to light the boat on fire using only the bronze mirrors available in Archimedes' time were unsuccessful, and the time taken to ignite the craft would have made its use impractical, resulting in the MythBusters team deeming the myth "busted". It was however found that the mirrors made it very difficult for the passengers of the targeted boat to see, likely helping to cause their defeat, which may have been the origin of the myth. (See solar power tower for a practical use of this technique.)
Due to its location in a steep-sided valley, the Italian town of Viganella gets no direct sunlight for seven weeks each winter. In 2006 a €100,000 computer-controlled mirror, 8×5 m, was installed to reflect sunlight into the town's piazza. In early 2007 the similarly situated village of Bondo, Switzerland, was considering applying this solution as well. In 2013, mirrors were installed to reflect sunlight into the town square in the Norwegian town of Rjukan. Mirrors can be used to produce enhanced lighting effects in greenhouses or conservatories.
Mirrors are a popular design theme in architecture, particularly with late modern and post-modernist high-rise buildings in major cities. Early examples include the Campbell Center in Dallas, which opened in 1972, and the John Hancock Tower in Boston.
More recently, two skyscrapers designed by architect Rafael Viñoly, the Vdara in Las Vegas and 20 Fenchurch Street in London, have experienced unusual problems due to their concave curved glass exteriors acting as respectively cylindrical and spherical reflectors for sunlight. In 2010, the Las Vegas Review Journal reported that sunlight reflected off the Vdara's south-facing tower could singe swimmers in the hotel pool, as well as melting plastic cups and shopping bags; employees of the hotel referred to the phenomenon as the "Vdara death ray", aka the "fryscraper." In 2013, sunlight reflecting off 20 Fenchurch Street melted parts of a Jaguar car parked nearby and scorching or igniting the carpet of a nearby barber shop. This building had been nicknamed the "walkie-talkie" because its shape was supposedly similar to a certain model of two-way radio; but after its tendency to overheat surrounding objects became known, the nickname changed to the "walkie-scorchie."
Painters depicting someone gazing into a mirror often also show the person's reflection. This is a kind of abstraction—in most cases the angle of view is such that the person's reflection should not be visible. Similarly, in movies and still photography an actor or actress is often shown ostensibly looking at him- or herself in the mirror, and yet the reflection faces the camera. In reality, the actor or actress sees only the camera and its operator in this case, not their own reflection.
The mirror is the central device in some of the greatest of European paintings:
Mirrors have been used by artists to create works and hone their craft:
Mirrors are sometimes necessary to fully appreciate art work:
Some other contemporary artists use mirrors as the material of art:
In the Middle Ages mirrors existed in various shapes for multiple uses. Mostly they were used as an accessory for personal hygiene but also as tokens of courtly love, made from ivory in the ivory carving centers in Paris, Cologne and the Southern Netherlands. They also had their uses in religious contexts as they were integrated in a special form of pilgrims badges or pewter/lead mirror boxes since the late 14th century. Burgundian ducal inventories show us that the dukes owned a mass of mirrors or objects with mirrors, not only with religious iconography or inscriptions, but combined with reliquaries, religious paintings or other objects that were distinctively used for personal piety. Considering mirrors in paintings and book illumination as depicted artifacts and trying to draw conclusions about their functions from their depicted setting, one of these functions is to be an aid in personal prayer to achieve self-knowledge and knowledge of God, in accord with contemporary theological sources. E.g. the famous Arnolfini-Wedding by Jan van Eyck shows a constellation of objects that can be recognized as one which would allow a praying man to use them for his personal piety: the mirror surrounded by scenes of the Passion to reflect on it and on oneself, a rosary as a device in this process, the veiled and cushioned bench to use as a prie-dieu, and the abandoned shoes that point in the direction in which the praying man kneeled. The metaphorical meaning of depicted mirrors is complex and many-layered, e.g. as an attribute of Mary, the “speculum sine macula”, or as attributes of scholarly and theological wisdom and knowledge as they appear in book illuminations of different evangelists and authors of theological treatises. Depicted mirrors – orientated on the physical properties of a real mirror – can be seen as metaphors of knowledge and reflection and are thus able to remind the beholder to reflect and get to know himself. The mirror may function simultaneously as a symbol and a device of a moral appeal. That is also the case if it is shown in combination with virtues and vices, a combination which also occurs more frequently in the 15th century: The moralizing layers of mirror metaphors remind the beholder to examine himself thoroughly according to his own virtuous or vicious life. This is all the more true if the mirror is combined with iconography of death. Not only is Death as a corpse or skeleton holding the mirror for the still living personnel of paintings, illuminations and prints, but the skull appears on the convex surfaces of depicted mirrors, showing the painted and real beholder his future face.
Mirrors are frequently used in interior decoration and as ornaments:
Mirrors play a powerful role in cultural literature.
Other types of reflecting device are also called "mirrors".
Black Mirror is a British science fiction anthology television series created by Charlie Brooker, with Brooker and Annabel Jones serving as the programme showrunners. It examines modern society, particularly with regard to the unanticipated consequences of new technologies. Episodes are standalone, usually set in an alternative present or the near future, often with a dark and satirical tone, though some are more experimental and lighter.
Black Mirror was inspired by older anthology series like The Twilight Zone, which were able to deal with controversial, contemporary topics without fear of censorship. Brooker developed Black Mirror to highlight topics related to humanity's relationship to technology, creating stories that feature "the way we live now – and the way we might be living in 10 minutes' time if we're clumsy."
The series premiered for two series on the British television channel Channel 4 in December 2011 and February 2013, respectively. After its addition to the catalogue in December 2014, Netflix purchased the programme in September 2015. It commissioned a series of 12 episodes later divided into the third and fourth series, each six episodes; the former was released on 21 October 2016 and the latter on 29 December 2017. A fifth series was announced on 5 March 2018. A standalone interactive film titled Black Mirror: Bandersnatch was released on 28 December 2018.
The series has garnered positive reception from critics, received many awards and nominations, and seen an increase in interest internationally, particularly in the United States after its addition to Netflix. Two episodes, "San Junipero" (from the third series) and "USS Callister" (fourth series), won a total of six Emmy Awards, with both episodes winning Outstanding Television Movie.Corporate spin-off
A corporate spin-off, also known as a spin-out, or starburst, is a type of corporate action where a company "splits off" a section as a separate business.Curved mirror
A curved mirror is a mirror with a curved reflecting surface. The surface may be either convex (bulging outward) or concave (recessed inward). Most curved mirrors have surfaces that are shaped like part of a sphere, but other shapes are sometimes used in optical devices. The most common non-spherical type are parabolic reflectors, found in optical devices such as reflecting telescopes that need to image distant objects, since spherical mirror systems, like spherical lenses, suffer from spherical aberration. Distorting mirrors are used for entertainment. They have convex and concave regions that produce deliberately distorted images.Daily Mirror
The Daily Mirror is a British national daily tabloid newspaper founded in 1903. It is owned by parent company Reach plc. From 1985 to 1987, and from 1997 to 2002, the title on its masthead was simply The Mirror. It had an average daily print circulation of 716,923 in December 2016, dropping markedly to 587,803 the following year. Its Sunday sister paper is the Sunday Mirror. Unlike other major British tabloids such as The Sun and the Daily Mail, the Mirror has no separate Scottish edition; this function is performed by the Daily Record and Sunday Mail, which incorporate certain stories from the Mirror that are of Scottish significance.
Originally pitched to the middle-class reader, it was converted into a working-class newspaper after 1934, in order to reach a larger audience. The Mirror has had a number of owners. It was founded by Alfred Harmsworth, who sold it to his brother Harold Harmsworth (from 1914 Lord Rothermere) in 1913. In 1963 a restructuring of the media interests of the Harmsworth family led to the Mirror becoming a part of International Publishing Corporation. During the mid 1960s, daily sales exceeded 5 million copies, a feat never repeated by it or any other daily (non-Sunday) British newspaper since. The Mirror was owned by Robert Maxwell between 1984 and 1991. The paper went through a protracted period of crisis after his death before merging with the regional newspaper group Trinity in 1999 to form Trinity Mirror.
During the 1930s the paper was editorially sympathetic to Oswald Mosley and the British Union of Fascists. The paper has consistently supported the Labour Party since the 1945 general election.Focus (optics)
In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge. Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by aberrations of the imaging optics. In the absence of significant aberrations, the smallest possible blur circle is the Airy disc, which is caused by diffraction from the optical system's aperture. Aberrations tend to get worse as the aperture diameter increases, while the Airy circle is smallest for large apertures.
An image, or image point or region, is in focus if light from object points is converged almost as much as possible in the image, and out of focus if light is not well converged. The border between these is sometimes defined using a "circle of confusion" criterion.
A principal focus or focal point is a special focus:
For a lens, or a spherical or parabolic mirror, it is a point onto which collimated light parallel to the axis is focused. Since light can pass through a lens in either direction, a lens has two focal points – one on each side. The distance in air from the lens or mirror's principal plane to the focus is called the focal length.
Elliptical mirrors have two focal points: light that passes through one of these before striking the mirror is reflected such that it passes through the other.
The focus of a hyperbolic mirror is either of two points which have the property that light from one is reflected as if it came from the other.Diverging (negative) lenses and convex mirrors do not focus a collimated beam to a point. Instead, the focus is the point from which the light appears to be emanating, after it travels through the lens or reflects from the mirror. A convex parabolic mirror will reflect a beam of collimated light to make it appear as if it were radiating from the focal point, or conversely, reflect rays directed toward the focus as a collimated beam. A convex elliptical mirror will reflect light directed towards one focus as if it were radiating from the other focus, both of which are behind the mirror. A convex hyperbolic mirror will reflect rays emanating from the focal point in front of the mirror as if they were emanating from the focal point behind the mirror. Conversely, it can focus rays directed at the focal point that is behind the mirror towards the focal point that is in front of the mirror as in a Cassegrain telescope.Hubble Space Telescope
The Hubble Space Telescope (HST) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. Although not the first space telescope, Hubble is one of the largest and most versatile and is well known as both a vital research tool and a public relations boon for astronomy. The HST is named after the astronomer Edwin Hubble and is one of NASA's Great Observatories, along with the Compton Gamma Ray Observatory, the Chandra X-ray Observatory and the Spitzer Space Telescope.With a 2.4-meter (7.9 ft) mirror, Hubble's four main instruments observe in the ultraviolet, visible, and near infrared regions of the electromagnetic spectrum. Hubble's orbit outside the distortion of Earth's atmosphere allows it to take extremely high-resolution images, with substantially lower background light than ground-based telescopes. Hubble has recorded some of the most detailed visible light images ever, allowing a deep view into space and time. Many Hubble observations have led to breakthroughs in astrophysics, such as accurately determining the rate of expansion of the universe.
The HST was built by the United States space agency NASA, with contributions from the European Space Agency. The Space Telescope Science Institute (STScI) selects Hubble's targets and processes the resulting data, while the Goddard Space Flight Center controls the spacecraft.Space telescopes were proposed as early as 1923. Hubble was funded in the 1970s, with a proposed launch in 1983, but the project was beset by technical delays, budget problems, and the Challenger disaster (1986). When finally launched in 1990, Hubble's main mirror was found to have been ground incorrectly, creating a spherical aberration, compromising the telescope's capabilities. The optics were corrected to their intended quality by a servicing mission in 1993.
Hubble is the only telescope designed to be serviced in space by astronauts. After launch by Space Shuttle Discovery in 1990, five subsequent Space Shuttle missions repaired, upgraded, and replaced systems on the telescope, including all five of the main instruments. The fifth mission was initially canceled on safety grounds following the Columbia disaster (2003). However, after spirited public discussion, NASA administrator Mike Griffin approved the fifth servicing mission, completed in 2009. The telescope is operating as of 2019, and could last until 2030–2040. After numerous delays, its successor, the James Webb Space Telescope (JWST), is scheduled to be launched in March 2021.James Webb Space Telescope
The James Webb Space Telescope (JWST or "Webb") is a space telescope that will be the successor to the Hubble Space Telescope. The JWST will provide greatly improved resolution and sensitivity over the Hubble, and will enable a broad range of investigations across the fields of astronomy and cosmology. One of its major goals is observing some of the most distant events and objects in the universe, such as the formation of the first galaxies. These types of targets are beyond the reach of current ground- and space-based instruments. Other goals include understanding the formation of stars and planets, and direct imaging of exoplanets and novas.
The JWST's primary mirror—the Optical Telescope Element—is composed of 18 hexagonal mirror segments made of gold-coated beryllium. These combine to create a 6.5-meter (21 ft 4 in) diameter mirror that is much larger than the Hubble's 2.4-meter (7 ft 10 in) mirror. Unlike the Hubble, which observes in the near ultraviolet, visible, and near infrared (0.1 to 1 μm) spectra, the JWST will observe in a lower frequency range from long-wavelength visible light through mid-infrared (0.6 to 27 μm). This will allow the JWST to observe high redshift objects that are too old and too distant for the Hubble and other earlier instruments to observe. The telescope must be kept very cold to observe in the infrared without interference, so it will be deployed in space near the Earth–Sun L2 Lagrangian point, and a large sunshield made of five sheets of silicon- and aluminum-coated Kapton will keep JWST's mirror and four science instruments below 50 K (−220 °C; −370 °F).
The JWST is being developed by NASA—with significant contributions from the Canadian Space Agency and the European Space Agency—and is named after James E. Webb, the American government official who was the administrator of NASA from 1961 to 1968 and played an integral role in the Apollo program. Development began in 1996, but the project has had numerous delays and cost overruns, and underwent a major redesign during 2005. The JWST's construction was completed in late 2016, after which its extensive testing phase began. In March 2018, NASA delayed the JWST's launch after the telescope's sunshield ripped during a practice deployment. The JWST's launch was delayed again in June 2018 following recommendations from an independent review board, and is currently scheduled for March 2021.Los Angeles Times
The Los Angeles Times (sometimes abbreviated as LA Times or L.A. Times) is a daily newspaper which has been published in Los Angeles, California, since 1881. It has the fourth-largest circulation among United States newspapers, and is the largest U.S. newspaper not headquartered on the East Coast. The paper is known for its coverage of issues particularly salient to the U.S. West Coast, such as immigration trends and natural disasters. It has won more than 40 Pulitzer Prizes for its coverage of these and other issues. As of June 18, 2018, ownership of the paper is controlled by Patrick Soon-Shiong, and the executive editor is Norman Pearlstine.In the nineteenth century, the paper was known for its civic boosterism and opposition to unions, the latter of which led to the bombing of its headquarters in 1910. The paper's profile grew substantially in the 1960s under publisher Otis Chandler, who adopted a more national focus. In recent decades, the paper's readership has declined and it has been beset by a series of ownership changes, staff reductions, and other controversies. In January 2018, the paper's staff voted to unionize, and in July 2018 the paper moved out of its historic downtown headquarters to a facility near Los Angeles International Airport.Man in the Mirror
"Man in the Mirror" is a song recorded by Michael Jackson, with lyrics by Siedah Garrett and music by Glen Ballard, and produced by Jackson and Quincy Jones. It peaked at number 1 in the United States when released in January 1988 as the fourth single from his seventh solo album, Bad (1987). It was nominated for Record of the Year at the Grammy Awards.
The song topped the Billboard Hot 100 for two weeks. The song peaked at number 21 in the UK Singles Charts in 1988, but in 2009, following the news of Jackson's death, the song peaked at number 2, having re-entered the chart at 11 the previous week as his top song on the singles chart. It also became the number 1 single in iTunes downloads in the US and the UK, having sold over 3 million digital copies in the former alone. The song was remixed for the soundtrack of Jackson's tribute tour Immortal.Pew Research Center
The Pew Research Center is a nonpartisan American fact tank based in Washington, D.C. It provides information on social issues, public opinion, and demographic trends shaping the United States and the world. It also conducts public opinion polling, demographic research, media content analysis, and other empirical social science research. The Pew Research Center does not take policy positions, and is a subsidiary of The Pew Charitable Trusts.Piers Morgan
Piers Stefan Pughe-Morgan (; né O'Meara; born 30 March 1965) is an English broadcaster, journalist, writer, and television personality. He is currently working on the ITV Breakfast programme Good Morning Britain.
Morgan began his career in Fleet Street as a writer and editor for several tabloid papers, including The Sun, News of the World, and the Daily Mirror. In 1994, aged 29, he was appointed editor of the News of the World by Rupert Murdoch, which made him the youngest editor of a British national newspaper in more than half a century. On television, he hosted Piers Morgan Live on CNN from 2011 to 2014, replacing Larry King Live in the timeslot following King's retirement. He was a judge on America's Got Talent and Britain's Got Talent. In 2008, Morgan won the seventh season of the US Celebrity Apprentice. In the UK, he has presented Piers Morgan's Life Stories since 2009, and Good Morning Britain since 2015. Morgan has written eight books, including four volumes of memoirs.
While working at Daily Mirror, he was in charge during the period that the paper was implicated in the phone hacking scandal. In 2011 Morgan denied having ever hacked a phone or "to my knowledge published any story obtained from the hacking of a phone". In 2012 he was criticised in the findings of the Leveson Inquiry by chair Brian Leveson who stated that comments made in Morgan's testimony about phone hacking were "utterly unpersuasive" and "that he was aware that it was taking place in the press as a whole and that he was sufficiently unembarrassed by what was criminal behaviour that he was prepared to joke about it".RAID
RAID (Redundant Array of Inexpensive Disks or Drives, or Redundant Array of Independent Disks) is a data storage virtualization technology that combines multiple physical disk drive components into one or more logical units for the purposes of data redundancy, performance improvement, or both. This was in contrast to the previous concept of highly reliable mainframe disk drives referred to as "single large expensive disk" (SLED).Data is distributed across the drives in one of several ways, referred to as RAID levels, depending on the required level of redundancy and performance. The different schemes, or data distribution layouts, are named by the word "RAID" followed by a number, for example RAID 0 or RAID 1. Each scheme, or RAID level, provides a different balance among the key goals: reliability, availability, performance, and capacity. RAID levels greater than RAID 0 provide protection against unrecoverable sector read errors, as well as against failures of whole physical drives.Reach plc
Reach plc (formerly known as Trinity Mirror between 1999 and 2018) is a British newspaper, magazine and digital publisher. It is one of Britain's biggest newspaper groups, publishing 240 regional papers in addition to the national Daily Mirror, Sunday Mirror, The Sunday People, as well as the Scottish Sunday Mail and Daily Record. Since purchasing Local World, it has gained 83 print publications. Trinity Mirror's headquarters are at Canary Wharf in London. Listed on the London Stock Exchange, it is a constituent of the FTSE SmallCap Index.
In February 2018, the company completed the acquisition of the UK publishing assets of Northern & Shell, including the Daily Express, Sunday Express, Daily Star and OK!. Following completion, Trinity Mirror announced a plan to rebrand as Reach, subject to investor approval which was achieved at its Annual General Meeting in May 2018.Snow White
"Snow White" is a 19th-century German fairy tale which is today known widely across the Western world. The Brothers Grimm published it in 1812 in the first edition of their collection Grimms' Fairy Tales. It was titled in German: Sneewittchen (in modern orthography Schneewittchen) and numbered as Tale 53. The name Sneewittchen was Low German and in the first version it was translated with Schneeweißchen. The Grimms completed their final revision of the story in 1854.The fairy tale features such elements as the magic mirror, the poisoned apple, the glass coffin, and the characters of the Evil Queen and the Seven Dwarfs. The seven dwarfs were first given individual names in the 1912 Broadway play Snow White and the Seven Dwarfs and then given different names in Walt Disney's 1937 film Snow White and the Seven Dwarfs. The Grimm story, which is commonly referred to as "Snow White", should not be confused with the story of "Snow-White and Rose-Red" (in German "Schneeweißchen und Rosenrot"), another fairy tale collected by the Brothers Grimm.
In the Aarne–Thompson folklore classification, tales of this kind are grouped together as type 709, Snow White. Others of this kind include "Bella Venezia", "Myrsina", "Nourie Hadig", "Gold-Tree and Silver-Tree", "The Young Slave", and "La petite Toute-Belle".Sunday Mirror
The Sunday Mirror is the Sunday sister paper of the Daily Mirror. It began life in 1915 as the Sunday Pictorial and was renamed the Sunday Mirror in 1963. In 2016 it had an average weekly circulation of 620,861, dropping markedly to 505,508 the following year. Competing closely with other papers, in July 2011, on the second weekend after the closure of the News of the World, more than 2,000,000 copies sold, the highest level since January 2000.The Daily Telegraph (Sydney)
The Daily Telegraph is an Australian daily tabloid newspaper published in Sydney, New South Wales, by Nationwide News Limited, a division of News Corp Australia, formerly News Limited.
The Daily Telegraph is published Monday through Saturday and is available throughout Sydney, across most of regional and remote New South Wales, the Australian Capital Territory and South East Queensland.
Amongst those ranked by Nielsen, the Telegraph's website is the 6th most popular Australian news website, and the most popular paid-subscription Australian news website. with a unique monthly audience of 2,841,381 readers.The Times of India
The Times of India (TOI) is an Indian English-language daily newspaper owned by The Times Group
It is the third-largest newspaper in India by circulation and largest selling English-language daily in the world according to Audit Bureau of Circulations (India). It is the oldest English-language newspaper in India still in circulation, albeit under different names since its first edition published in 1838. It is also the second-oldest Indian newspaper still in circulation after the Bombay Samachar.
Near the beginning of the 20th century, Lord Curzon, the Viceroy of India, called The Times of India "the leading paper in Asia". In 1991, the BBC ranked The Times of India among the world's six best newspapers.It is owned and published by Bennett, Coleman & Co. Ltd. (B.C.C.L.), which is owned by the Sahu Jain family. In the Brand Trust Report 2012, The Times of India was ranked 88th among India's most-trusted brands. In 2017, however, the newspaper was ranked 355th.Twin
Twins are two offspring produced by the same pregnancy. Twins can be either monozygotic ('identical'), meaning that they develop from one zygote, which splits and forms two embryos, or dizygotic ('fraternal'), meaning that each twin develops from a separate egg and each egg is fertilized by its own sperm cell.In contrast, a fetus that develops alone in the womb is called a singleton, and the general term for one offspring of a multiple birth is multiple. Non-related look-alikes whose resemblance parallels that of twins are referred to as doppelgangers.Zizhi Tongjian
The Zizhi Tongjian (Chinese: 資治通鑑; literally: 'Comprehensive Mirror in Aid of Governance') is a pioneering reference work in Chinese historiography, published in 1084 in the form of a chronicle. In 1065 AD, Emperor Yingzong of Song ordered the great historian Sima Guang (1019–1086 AD) to lead with other scholars such as his chief assistants Liu Shu, Liu Ban and Fan Zuyu, the compilation of a universal history of China. The task took 19 years to be completed, and, in 1084 AD, it was presented to his successor Emperor Shenzong of Song. The Zizhi Tongjian records Chinese history from 403 BC to 959 AD, covering 16 dynasties and spanning across almost 1,400 years, and contains 294 volumes (卷) and about 3 million Chinese characters.