R The letter R is the eighteenth letter in the Latin alphabet. Its name in English language is ar, pronounced that is in Received Pronunciation and other rhotic and non-rhotic accents accents of English, and in General American and other rhotic and non-rhotic accents accents.
	R. J. Mitchell For the author, see R J Mitchell Reginald Joseph Mitchell CBE was an aeronautical engineering , most notable for his design of the Supermarine Spitfire. R. J. Mitchell was born in the village of Talke, Newcastle-under-Lyme, in England. After leaving Hanley High School at the age of 16 he gained an apprenticeship at Kerr Stuart & Co.
	Ra Ra is the Solar deity of Heliopolis in ancient Egypt. In later Egyptian dynastic times, Ra was subsumed into the god Horus, as Re-Horakhty . The sun is either the symbolic interpretation of Ra, his entire body, or just his eye. The symbols of Ra are the solar symbols of a golden disk or the symbol ? .
	Rabat Rabat , population 1.2 million , is the capital of the Morocco. It is also the capital of the Rabat-Sal-Zemmour-Zaer region. The city is located on the Atlantic Ocean at the mouth of the river Bou Regreg. On the facing shore of the river lies Sal, Rabat's bedroom community.
	Rabbet A rabbet is a recess or groove cut into the edge of a piece of machineable material, usually wood. When viewed in cross-section, a rabbet is two-sided and open to the edge or end of the surface into which it is cut. The spelling rabbet is probably a derivation of rebate, the latter being more common outside of North America.
	Rabbit Rabbits are small mammals in the order Lagomorpha of the family Leporidae, found in many parts of the world. They are sometimes affectionately known as bunnies or bunny rabbits, especially by children. There are seven different genus in the family taxonomy as rabbits, including the European Rabbit , cottontail rabbits , and the Amami Rabbit .
	Rabbiteye blueberry Rabbiteye Blueberry is a species of blueberry native to the southeastern United States, from North Carolina south to Florida and west to Texas. Other common names include Southern Highbush Blueberry, Southern Black Blueberry, and Smallflower Blueberry. It is a deciduous shrub growing to 4 m tall, though usually less, commonly only 1-2 m tall.
	Rabbitfish Rabbitfishes are perciform fishes in the family Siganidae. Rabbitfishes are found in shallow lagoons in the Indo-Pacific and eastern Mediterranean. Some live in schools, while others live more solitary lives among the corals. Rabbitfishes have small, hare-like mouths, large dark eyes, and a peaceful temperament which gives them their name.
	Rabble rabble is a Canada website. Among other services, it publishes journalism on a daily basis primarily relating to social justice and progressivism politics. The site also hosts , a politically-oriented Internet forum, and also the rabble podcasting network, or and the .
	Rabies Rabies is a virus disease that causes acute encephalitis in animals and people. It can affect most species of warm-blooded animals, but is almost non-existent among herbivores, and some species of hyena may carry the virus without developing the disease. In unvaccinated humans, rabies is almost invariably fatal once full-blown symptoms have developed, but prompt post-exposure vaccination usually prevents symptoms from developing.
	Rabindranath Tagore Rabindranath Tagore.jpg|thumb|200px|right|A Bust of Tagore in the Sardar Vallabhbhai Patel National Memorial's Tagore Memorial Room.]] Tagore's post-death impact can be felt through the many festivals held worldwide in his honour — examples include the annual Bengali festival/celebration of Kabipranam, the annual Tagore Festival held in Urbana, Illinois in the United States, the Rabindra Path Parikrama walking pilgrimages leading from Calcutta to Shantiniketan, and ceremonial recitals of Tagore's poet
	Raccoon Raccoons are nocturnal mammals in the genus Procyon of the Procyonidae Scientific classification. Raccoons are unusual for their thumbs, which enable them to open many closed containers and doors. They are intelligent omnivores with a reputation for being clever, sly, and mischievous.
	Raccoon Dog The Raccoon Dog is a member of the canidae indigenous to east Asia. It is the only species in its genus Nyctereutes. It is named for its resemblance to the raccoon, to whom it is only distantly related. The animal is also known under the Japanese language name tanuki, where it carries historical and cultural significance.
	Race The term race distinguishes one population of an animal species from another of the same species. Many regard race as a social construction. The most widely used human racial categories are based on visible Trait s , genes, and self-identification. Conceptions of race, as well as specific racial groupings, vary by culture and over time and are often controversial issue, for scientific reasons as well as their impact on social identity and identity politics.
	Race riot A race riot or racial riot is an outbreak of violent civil unrest in which race is a key factor. The term had entered the English language in the United States by the 1890s. Early use of the term in the United States referred to race riots which were often a dominant culture mob action against individuals or groups of people from other races.
	Raceme A raceme is a type of inflorescence that is unbranched and indeterminate growth and bears pedicellate flowers — flowers having short floral stalks called pedicels — along the axis. In botany, axis means a shoot, in this case one bearing the flowers.
	Rachel Carson Rachel Louise Carson was a Pittsburgh, Pennsylvania, Pennsylvania-born zoologist and Marine biology whose landmark book, Silent Spring, is often credited with having launched the global environmental movement. Silent Spring had an immense effect in the United States, where it spurred a reversal in national pesticide policy.
	Rachis The rachis is the main axis of the inflorescence, or spike, of wheat and other cereals, to which the spikelets are attached. It is also the part of the petiole that the pinnae are attached to in ferns, or the main stem of a compound leaf. Spikelets are small inflorescences bearing one or more florets, or small flowers, along with a set of miniature bractlike leaves.
	Racial segregation Racial segregation is characterized by separation of people of different races in daily life when both are doing equal tasks, such as eating in a restaurant, drinking from a water fountain, using a rest room, attending school, going to the movies, or in the rental or purchase of a home. Segregation may be de jure —mandated by law—or de facto ; de facto segregation may exist even illegally.
	Racialism Racialism is an emphasis on race or racial considerations. Sometimes racialism refers to the controversial belief in the existence and significance of race categories. Racialism was very common throughout Europe, North America, and Australia through the 18th and 19th centuries, and continues on to a lesser degree today.
	Racing ---- A race is a competition of speed. The competitors in a race try to complete a given task in the shortest amount of time. Typically this involves traversing some distance, but it can be any other task involving speed. A race to cover a certain distance may be any length, and using any means stipulated by the rules.
	Racing shell In watercraft, a shell or racing shell is an extremely narrow, and often disproportionately long, rowing boat specifically intended for sport rowing or exercise. It's long length and semi-circula cross-section are intended to reduce drag to a minimum. This makes them unstable and liable to tip.
	Racism Racism is a belief in the moral or biological superiority of one race or ethnic group over another or others. The term racism is also sometimes used to refer to preference for one's own ethnic group , fear of difference , views or preferences against interbreeding of the races , and nationalism, regardless of any explicit belief in superiority or inferiority fact.
	Rack and pinion A rack and pinion is a pair of gears which convert rotational motion into linear motion. The circular pinion engages teeth on a flat bar - the rack. Rotational motion applied to the pinion will cause the rack to move to the side, up to the limit of its travel. The rack and pinion arrangement is commonly found in the steering mechanisms of automobiles or other wheeled, steered vehicles.
	Rack railway A cog railway, rack-and-pinion railway or rack railway is a railway with a special toothed rack and pinion or rack mounted on the railroad ties between the running Rail tracks#railway rail. The trains are fitted with one or more gear or pinions that mesh with this rack and pinion.
	Racon A Racon is a type of radar transponder commonly used to mark maritime navigational hazards. The word is an acronym for RAdar beaCON. When a racon receives a radar pulse, it responds with a signal on the same frequency which leaves an image on the radar display. This takes the form of a short line of dots and dashes forming a morse code character radiating away from the location of the beacon on the normal plan position indicator radar display.
	Racoon Racoon is a Netherlands rock band, formed in 1997. Their first big appearance was at the 1999 Noorderslagfestival, after which the record companies stood in line to make the band an offer. First album Till Monkeys Fly appeared in January 2000, produced by Michael Schoots.
	Racquet A racquet is a sports implement consisting of a handled frame with an open hoop across which a network of cord is stretched. It is used for catching or striking a ball in such games as squash , tennis, racquetball, and badminton. Collectively, these games are known as List of sports#Racquet sports.
	Racquetball Racquetball is a sport played with racquets and a hollow rubber ball on an indoor or outdoor court. It was invented by Joe Sobek in 1949 in sports incorporating rules from Squash and American_handball. Unlike most List of sports#Racquet sports , usage of the walls, floor, and ceiling of the court is considered legal in the context of the sport, rather than out-of-bounds.
	Radar RADAR is a system that uses radio waves to detect, determine the direction and distance and/or speed of objects such as aircraft, ships, terrain or rain and map them. A transmitter emits radio waves, which are reflected by the target, and detected by a receiver, typically in the same location as the transmitter.
	Radclyffe Hall Radclyffe Hall, was a United Kingdom poet and author of the acclaimed lesbian novel The Well of Loneliness.
	Radial engine The radial engine is a engine configuration of internal combustion engine, in which the cylinders are arranged pointing out from a central crankshaft like the spokes on a wheel. This configuration was formerly very commonly used in aircraft engines before being superseded by turboshaft and turbojet engines.
	Radial tire A radial tire is a particular design of automobile tire. The design was originally developed by Michelin in 1946 but, because of its advantages, has now become the standard design for essentially all automotive tires. Tires are not fabricated just from rubber; they would be far too flexible and weak.
	Radian The radian is a unit of plane angle. It is represented by the symbol "rad" or, more rarely, by the superscript c . For example, an angle of 1.2 radians would be written "1.2 rad" or "1.2c ". The radian was formerly an SI supplementary unit, but this category was abolished from the SI system in 1995
	Radiation pattern In the field of antenna design the term radiation pattern most commonly refers to the directional dependence of radiation from the antenna or other source . Particularly in the fields of fiber optics, lasers, and integrated optics, the term radiation pattern, or near-field radiation pattern, may also be used as a synonym for the near-field pattern or Fresnel pattern.
	Radiation therapy Radiation therapy is the medicine use of ionizing radiation as part of cancer oncology to control malignant cell s . Radiotherapy may be used for curative or adjuvant cancer treatment. It is often used as a palliative treatment, where cure is not possible and the aim is for local disease control or symptomatic relief.
	Radiator This article discusses radiators in automobiles, buildings, and electronics. For planckian radiators see black body. For the album by Super Furry Animals, see Radiator. A radiator is a device designed to transfer thermal energy from one medium to another for the purpose of cooling and heating.
	Radio Radio is the wireless, by modulation of electromagnetic radiation with frequency below those of light.
	Radio astronomy Radio astronomy is the study of celestial phenomena through measurement of the characteristics of radio waves emitted by physical processes occurring in space. Radio waves are much longer than light waves. In order to receive good signals, radio astronomy requires large antennas, or arrays of smaller antennas all working together.
	Radio beacon A radio beacon is non-directional transmitter that usually transmits a constant Signalling on a specified radio frequency. Before the days of VHF omnidirectional range, GPS, LORAN, beacons were used with direction finding equipment to find ones relative Bearing to a known location.
	Radio frequency Radio frequency, or RF, refers to that portion of the electromagnetic spectrum in which electromagnetic waves can be generated by alternating current fed to an antenna . Such frequencies and the belonging wavelength account for the following parts of the spectrum shown in the table below.
	Radio telescope A radio telescope is a form of radio receiver used in astronomy. In contrast to an "ordinary" telescope, which receives visible light, a radio telescope "sees" radio waves emitted by radio sources, typically by means of a large parabola antenna , or arrays of them.
	Radio-controlled aircraft Radio-controlled aircraft are small model aircraft that can be controlled remotely. They use radio control with a hand-held transmitter and a receiver within the craft. The receiver controls the corresponding servomechanisms that move the control surfaces based on the position of joysticks on the transmitter, which in turn maneuvers the plane.
	Radioactive decay Radioactive decay is the set of various processes by which unstable atomic nucleus emit subatomic particles. Decay is said to occur in the parent nucleus and produces a daughter nucleus. This is a random process, i.e. it is impossible to predict the decay of individual atoms.
	Radioactive waste Radioactive waste is waste type containing radioactive decay chemical elements that does not have a practical purpose. It is sometimes the product of a nuclear process, such as nuclear fission. The majority of radioactive waste is "low-level waste", meaning it has low levels of radioactivity per mass or volume.
	Radiocarbon dating Radiocarbon dating is a radiometric dating method that uses the naturally occurring isotope carbon-14 to determine the age of carbonaceous materials up to . Within archaeology it is considered an absolute dating technique. The technique was discovered by Willard Libby and his colleagues in 1949 during his tenure as a professor at the University of Chicago.
	Radiolarian Radiolarians are amoeboid protozoa that produce intricate mineral skeletons, typically with a central capsule dividing the cell into inner and outer portions, called endoplasm and ectoplasm. They are found as plankton throughout the ocean, and because of their rapid turn-over of species, their tests are important Fossils found from the Cambrian onwards.
	Radiology Radiology is the medical specialty directing medical imaging technologies to diagnose and sometimes treat diseases. Traditionally it was the branch of medicine science dealing with the medical use of X-rays emitted by X-ray machines or other such radiation devices for the purpose of obtaining visual information as part of medical imaging.
	Radish The radish is a root vegetable of the Brassicaceae family. The most popular part for eating is the napiform Taproot, although the entire plant is edible and the tops can be used as a leaf vegetable. The skin comes in a variety of colours. Most commonly known is the round, red-skinned variety.
	Radome A radome is a weatherproof enclosure used to protect an antenna.
	Raffinose Raffinose is a complex carbohydrate, a trisaccharide composed of galactose, fructose, and glucose. It can be found in beans, cabbage, brussels sprouts, broccoli, asparagus, other vegetables, and whole grains. Raffinose is hydrolysis to D-galactose and sucrose by alpha galactosidase.
	Rafflesiaceae Rafflesiaceae is a family of parasitic plants found in east and southeast Asia, including Rafflesia arnoldii, the plant with the largest flower of all plants. Rafflesiaceae was considered an unplaced family in the APG II system, while other authors placed it into the order Rafflesiales together with some other families of parasitic plants.
	Raft A raft is any flat floating structure for travel over water. It is the most basic of boat design, characterized by the absence of a hull. Traditional or primitive rafts are constructed of wood or reeds. Modern rafts use durable, multi-layered rubberized fabrics. Depending on its use and size, it may or may not have a superstructure, masts, or rudders.
	Ragamuffin The Ragamuffin is a breed of domestic cat which first made its appearance in 1994. They are adoptable as early as four months of age, but do not reach full maturity until around four years of age. They have fur like rabbits, personalities usually associated with dogs and bodies which are larger than typical domestic cats.
	RAGE RAGE, the receptor for advanced glycation endproducts is a 35kD transmembrane receptor of the immunoglobulin super family which was first characterized in 1992 by Neeper et. al. Its name comes from its ability to bind advanced glycation endproduct which is thought to result in pro-inflammation gene activation.
	Ragged Robin Ragged Robin is a plant of the family Caryophyllaceae. A European native found in wet meadows, it grows to about 75cm high. The pink-purple petals are each divided into two or three lobes giving the flower an untidy, ragged appearance.
	Raglan Raglan is a seaside town and surrounding district associated with Whaingaroa Harbour on the west coast of the Waikato region in New Zealand's North Island. The harbour runs about 12km inland from the entrance and for the most part is less than 2km wide, and is the northernmost of three large inlets in the Waikato coast.
	Ragnar Anton Kittil Frisch Ragnar Anton Kittil Frisch was a Norway economist. Frisch was born in Oslo. His father was silversmith Anton Frisch and mother Ragna Fredrikke b. Kittilsen. Grandfather of Norwegian TV personality Nadia Hasnoui. He received a degree in economics from the University of Oslo in 1919 and studied in Paris and England before gaining a Ph.D in mathematical statistics in 1925.
	Ragtime Ragtime is an United States musical genre enjoying its peak popularity between 1899–1918. It has had several periods of revival in popularity and is still being composed today. Ragtime was the first truly American musical genre, preceding Jazz. It began as dance music in popular music settings years before being published as popular sheet music for piano.
	Ragweed Ragweeds is a genus of flowering plants from the sunflower family. The name of this genus is derived from the Greek word for "food of the gods". They occur in temperate regions of the northern hemisphere and South America. They prefer dry, sunny grassy plains; sandy soils; and to grow along river banks, along roadsides, disturbed soils, vacant lots and ruderal sites.
	Ragwort Ragwort is a very common wild flower in the family Asteraceae that is found throughout Europe, usually in dry, open places, and has also been widely distributed as a weed elsewhere. (For the North American species, see Packera obovata.) Alternative names include Cushag, Tansy Ragwort, St.
	Rahu In Hindu mythology, Rahu is a snake that swallows the sun or the moon causing eclipses. He is depicted in art as a dragon with no body riding a chariot drawn by eight black horses. According to myth, during the Samudra manthan, the asura Rahu drank some of the divine nectar.
	RAID In computing, the acronym RAID refers to a data storage scheme using multiple hard drives to share or replicate data among the drives. Depending on the level chosen, the benefit of RAID is one or more of increased data integrity, fault-tolerance, throughput or disk storage compared to single drives.
	Railcar A railcar is a self-propelled Rail transport vehicle designed to transport passengers. The term "railcar" is usually used in reference to a train consisting of a single Coach, with a driver's cab at each end. The term is sometimes also used as an alternative name for the small types of multiple unit which consist of more than one coach.
	Railroad car A railroad car, also known as an item of rolling stock, is a vehicle on a railroad that is not a locomotive — one that provides another purpose than purely haulage, although some types of car are powered. Cars can be coupled together into a train, either hauled by one or more locomotives or self-propelled.
	Railroad tie A railroad tie, cross tie, or sleeper is a rectangular object used as a base for railroad tracks. Traditionally, ties have been made of wood, often heavily creosoted or, less often, treated with other preservatives, but steel has also been used and concrete is now widely used.
	Rain Rain is a form of Precipitation , other forms of which include snow, sleet, hail, and dew. Rain forms when separate drops of water fall to the Earth's surface from clouds. Not all rain reaches the surface, however; some evaporates while falling through dry air.
	Rain gauge A rain gauge is a type of instrument used by Meteorology and hydrologists to gather and measure the amount of liquid precipitation over a set period of time. Most rain gauges generally measure the precipitation in millimetres. The level of rainfall is sometimes reported as inches or centimetres.
	Rain shadow A rain shadow is a dry region on the surface of the Earth that is leeward or behind a mountain with respect to the prevailing wind direction. A rain shadow area is dry because, as moist air masses rise to top a mountain range or large mountain, the air cools and water vapor condenses as rain or snow, falling on the windward side or top of the mountain.
	Rain-in-the-Face Rain-in-the-Face was a warchief of the Lakota tribe of Native Americans in the United States. His mother was a Dakotah related to the band of famous Chief Inkpaduta. He was among the Indian leaders who defeated George Armstrong Custer and the U.S. 7th Cavalry Regiment at the 1876 Battle of Little Big Horn.