polar air mass, air mass that forms over land or water in the higher latitudes. See air mass;

polar air mass, air mass that forms over land or water in the higher latitudes. See air mass;

polar coordinates, system of locating points in a plane with reference to a fixed point O (the origin) and a ray from the origin usually chosen to be the positive x-axis. The coordinates are written (r,θ), in which ris the distance from the origin to any desired point P and θis the angle made by

geomagnetic field: Outer magnetic field: …field lines split are called polar cusps. The projection of the polar cusps on the atmosphere at about 72° magnetic latitude creates the dayside auroral ovals. Auroras can be seen in these regions in the dark hours of winter, but they are much weaker than on the nightside because the…

polar vortex, large area of persistent low pressure generally located above each of Earth’s polar regions and containing a mass of extremely cold air. The altitude of this cyclone extends from the middle of the troposphere (the lowest level of Earth’s atmosphere, which spans the region from the

polar ecosystem: Biota of the Arctic: The true polar desert generally occurs on coastal areas fringing the Arctic Ocean and on areas of a few hundred metres elevation in the extreme High Arctic where soils have not developed and the frost-free period and soil moisture are insufficient for most plant growth. The occasional…

atmospheric circulation: …and equatorward as the polar easterlies. In the northern polar regions, where water and land are interspersed, the polar easterlies give way in summer to variable winds.

polar ecosystem, complex of living organisms in polar regions such as polar barrens and tundra. Polar barrens and tundra are found at high latitudes on land surfaces not covered by perpetual ice and snow. These areas lying beyond the tree line comprise more than 10 percent of the Earth’s land

carboxylic acid: Acidity: …one example of the so-called inductive effect, in which a substituent affects a compound’s distribution of electrons. There are a number of such effects, and atoms or groups may be electron-withdrawing or electron-donating as compared with hydrogen. The presence of such groups near the COOH group of a carboxylic acid…

the Andrews Sisters: … (1987), Jakob the Liar (1999), The Polar Express (2004), and The Chronicles of Narnia (2005).

Chris Van Allsburg: The Polar Express (1985) earned Van Allsburg another Caldecott Medal. The tale of a boy’s magical train ride to the North Pole on Christmas Eve, brought to life by Van Allsburg’s dreamlike illustrations in hues of blue and purple, ranks among the best-selling children’s books…

geoid: Flattening (f) is defined as the difference in magnitude between the semimajor axis (a) and the semiminor axis (b) divided by the semimajor axis, or f = (a − b)/a. For Earth the semimajor axis and semiminor axis differ by about 21 kilometres (13 miles),…

Arctic fox, (Vulpes lagopus), northern fox of the family Canidae, found throughout the Arctic region, usually on tundra or mountains near the sea. Fully grown adults reach about 50–60 cm (20–24 inches) in length, exclusive of the 30-cm (12-inch) tail, and a weight of about 3–8 kg (6.6–17 pounds).

polar front, in meteorology, the transition region separating warmer tropical air from colder polar air in the mid-latitudes. This region possesses a strong temperature gradient, and thus it is a reservoir of potential energy that can be readily tapped and converted into the kinetic energy

polar front jet stream, a belt of powerful upper-level winds that sits atop the polar front. The winds are strongest in the tropopause, which is the upper boundary of the troposphere, and move in a generally westerly direction in midlatitudes. The vertical wind shear which extends below the core of

polar front jet stream, a belt of powerful upper-level winds that sits atop the polar front. The winds are strongest in the tropopause, which is the upper boundary of the troposphere, and move in a generally westerly direction in midlatitudes. The vertical wind shear which extends below the core of

glacier: Mass balance: A polar glacier is defined as one that is below the freezing temperature throughout its mass for the entire year; a subpolar (or polythermal) glacier contains ice below the freezing temperature, except for surface melting in the summer and a basal layer of temperate ice; and…

polar vortex, large area of persistent low pressure generally located above each of Earth’s polar regions and containing a mass of extremely cold air. The altitude of this cyclone extends from the middle of the troposphere (the lowest level of Earth’s atmosphere, which spans the region from the

Sir Ranulph Fiennes: … (OBE) in 1993 and the Polar Medal in 1984 (recognized again in 1995 for his work in both polar regions). Many of the endeavours undertaken by Fiennes were fund-raisers, and over the years he raised millions for a variety of charities.

polar motion, a periodic rotation of the Earth’s spin axis about a mean axis, somewhat like the wobble of a spinning top. Slight variations in latitude and longitude result from this wobble because the poles are displaced from their mean positions. The north pole of rotation rotates

plant reproductive system: Angiosperms: …with the two nuclei (polar nuclei) within the large central cell of the female gametophyte. The resultant nucleus, which has three sets of chromosomes, is the primary endosperm nucleus. This process, double fertilization, occurs only in angiosperms.

plant reproductive system: Angiosperms: …with the two nuclei (polar nuclei) within the large central cell of the female gametophyte. The resultant nucleus, which has three sets of chromosomes, is the primary endosperm nucleus. This process, double fertilization, occurs only in angiosperms.

spaceflight: Earth orbit: …to be put into a polar orbit—an orbit that crosses over Earth’s poles—it is launched in a northerly or southerly direction. Although the benefit of an easterly launch is lost, a spacecraft in an orbit perpendicular to the Equator offers other advantages. As Earth turns on its axis, the spacecraft…

North America: Air masses: …maritime tropical, and the maritime polar Pacific are the most influential air masses. Polar continental air reflects the spread of a negative temperature anomaly over much of the continent. It is a dry, cool-to-cold mass of stable air forming under an immense dome of high pressure above the Canadian Shield,…

map: Map projections: The polar projection is an azimuthal projection drawn to show Arctic and Antarctic areas. It is based on a plane perpendicular to the Earth’s axis in contact with the North or South Pole. It is limited to 10 or 15 degrees from the poles. Parallels of…

polar region, area around the North Pole or the South Pole. The northern polar region consists mainly of floating and pack ice, 7–10 feet (2–3 m) thick, floating on the Arctic Ocean and surrounded by land masses. The ice cap of the southern polar region averages 6,700 feet (about 2,000 m) in

Chandrayaan: A Polar Satellite Launch Vehicle launched the 590-kg (1,300-pound) Chandrayaan-1 on October 22, 2008, from the Satish Dhawan Space Centre on Sriharikota Island, Andhra Pradesh state. The probe then was boosted into an elliptical polar orbit around the Moon, 504 km (312 miles) high at its…

ozone depletion: Antarctic ozone hole: …on particles that make up polar stratospheric clouds (PSCs) in the lower stratosphere.

Ural Mountains: Physiography: The northernmost Polar Urals extend some 240 miles (400 km) from Mount Konstantinov Kamen in the northeast to the Khulga River in the southeast; most mountains rise to 3,300–3,600 feet (1,000–1,100 metres) above sea level, although the highest peak, Mount Payer, reaches 4,829 feet (1,472 metres). The…

polar vortex, large area of persistent low pressure generally located above each of Earth’s polar regions and containing a mass of extremely cold air. The altitude of this cyclone extends from the middle of the troposphere (the lowest level of Earth’s atmosphere, which spans the region from the

polar wandering, the migration of the magnetic poles over Earth’s surface through geologic time. The study of polar wandering began in the early 20th century with Austrian priest and geologist Damian Kreichgauer and German scientists Wladimir Köppen and Alfred Wegener, who proposed the first paths

Mount Erebus disaster: Investigations: …front of them because of polar whiteout, which occurs when low-lying clouds gather above clear air. The clouds reflect light and keep any snow-covered features from casting shadows, making the sky, snow-covered land, and horizon blend together. Under those conditions, it is almost impossible for pilots to see elevated surfaces.

polar vortex, large area of persistent low pressure generally located above each of Earth’s polar regions and containing a mass of extremely cold air. The altitude of this cyclone extends from the middle of the troposphere (the lowest level of Earth’s atmosphere, which spans the region from the

polarimetry, in analytic chemistry, measurement of the angle of rotation of the plane of polarized light (that is, a beam of light in which the vibrations of the electromagnetic waves are confined to one plane) that results upon its passage through certain transparent materials. Polarimetry is of

Polaris, Earth’s present northern polestar, or North Star, at the end of the “handle” of the so-called Little Dipper in the constellation Ursa Minor. Polaris will be closest to the north celestial pole in about 2100, and, because of the precession of Earth’s axis, in several centuries Polaris will

Fay Weldon: …radio plays Spider (1973) and Polaris (1978) and the stage plays Words of Advice (1974) and Action Replay (1979).

Polaris missile: …nuclear-powered submarines armed with 16 Polaris missiles each. Each missile was 31 feet (9.4 m) long and 4.5 feet (1.4 m) in diameter and was powered by two solid-fueled stages. Three models were developed: the A-1, with a range of 1,400 miles (2,200 km) and a one-megaton nuclear warhead; the…

Polaris missile: …a one-megaton nuclear warhead; the A-2, with a 1,700-mile (2,700-kilometre) range and a one-megaton warhead; and the A-3, capable of delivering three 200-kiloton warheads a distance of 2,800 miles (4,500 km).

Polaris missile: …a one-megaton warhead; and the A-3, capable of delivering three 200-kiloton warheads a distance of 2,800 miles (4,500 km).

Polaris missile: …it into the A-3TK, or Chevaline, system, which was fitted with such devices as decoy warheads and electronic jammers for penetrating Soviet ballistic-missile defenses around Moscow. In 1980 the United Kingdom announced plans to replace its Polaris force with the Trident SLBM in the 1990s.

polestar: …pole; the present southern polestar, Polaris Australis (also called σ Octantis), is only of the 5th magnitude and is thus barely visible to the naked eye.

Polaris missile, first U.S. submarine-launched ballistic missile (SLBM) and the mainstay of the British nuclear deterrent force during the 1970s and ’80s. After four years of research and development, the U.S. Navy in 1960 began to deploy nuclear-powered submarines armed with 16 Polaris missiles

regeneration: Polarity and gradient theory: Each living thing exhibits polarity, one example of which is the differentiation of an organism into a head, or forward part, and a tail, or hind part. Regenerating parts are no exception; they exhibit polarity by always growing in a distal…

geomagnetic field: Characteristics of Earth’s magnetic field: …Earth with the north geographic pole at the top of the diagram, the magnet must be oriented with its north magnetic pole downward toward the south geographic pole. Then, as shown in the diagram, magnetic field lines leave the north pole of the magnet and curve around until they cross…

polarity, in chemical bonding, the distribution of electrical charge over the atoms joined by the bond. Specifically, while bonds between identical atoms, as in H2, are electrically uniform in the sense that both hydrogen atoms are electrically neutral, bonds between atoms of different elements are

Earth: The geomagnetic field and magnetosphere: …of Earth’s magnetic field is polarity reversal. In this process the direction of the dipole component reverses—i.e., the north magnetic pole becomes the south magnetic pole and vice versa. From studying the direction of magnetization of many rocks, geologists know that such reversals occur, without a discernible pattern, at intervals…

collective behavior: Short-term effects: …of collective behavior contribute to polarizations, forcing people to take sides on issues and eliminating the middle ground. Often a three-sided conflict develops among the two polarized groups and mediators who wish to de-emphasize divisive issues altogether. Third, every instance of collective behavior either alters or strengthens the makeup of…

polarization, property of certain electromagnetic radiations in which the direction and magnitude of the vibrating electric field are related in a specified way. Light waves are transverse: that is, the vibrating electric vector associated with each wave is perpendicular to the direction of

microscope: Polarizing microscopes: A second filter, a polarization analyzer, is fitted to the eyepiece, where it blocks out all but one polarization of the light. The analyzer can be rotated to obtain maximum contrast in the image, and so the direction of polarization of the light transmitted through the object can be…

microscope: Polarizing microscopes: …also be equipped with a polarization retarder, which shifts the phase of the light between selected polarization directions and which can be rotated to measure the amount of elliptic polarization produced by the specimen.

Brewster’s law, relationship for light waves stating that the maximum polarization (vibration in one plane only) of a ray of light may be achieved by letting the ray fall on a surface of a transparent medium in such a way that the refracted ray makes an angle of 90° with the reflected ray. The law

liquid: Speed of sound and electric properties: …negligible conductivities, but they are polarized by an electric field; that is, the liquid develops positive and negative poles and also a dipole moment (which is the product of the pole strength and the distance between the poles) that is oriented against the field, from which the liquid acquires energy.…

electric polarization, slight relative shift of positive and negative electric charge in opposite directions within an insulator, or dielectric, induced by an external electric field. Polarization occurs when an electric field distorts the negative cloud of electrons around positive atomic nuclei

radiation: Double refraction: …said to be plane-polarized, the plane of polarization being the one that contains the propagation direction and the electric vector. In the case of elliptic polarization, the field vector generates an ellipse in a plane perpendicular to the propagation direction as the wave proceeds. Circular polarization is a special case…

optical activity, the ability of a substance to rotate the plane of polarization of a beam of light that is passed through it. (In plane-polarized light, the vibrations of the electric field are confined to a single plane.) The intensity of optical activity is expressed in terms of a quantity,

Sahara desert ant: Navigation: …ants in fact do use polarized light as a compass, augmenting the pedometric function of their legs. Upon approaching the nest, the ants then begin using visual and olfactory cues to find the exact location of the entrance.

region: Regions may be nodal, defined by the organization of activity about some central place (e.g., a town and its hinterland, or tributary area), or uniform, defined by the homogeneous distribution of some phenomena within it (e.g., a tropical rainforest).

Polaroid Corporation: …invention, an inexpensive plastic-sheet light polarizer. By 1936 Land began to use polarized material in sunglasses and other optical devices, and in 1937 the company was incorporated under the Polaroid name.

Brewster’s law, relationship for light waves stating that the maximum polarization (vibration in one plane only) of a ray of light may be achieved by letting the ray fall on a surface of a transparent medium in such a way that the refracted ray makes an angle of 90° with the reflected ray. The law

optics: Filters and thin films: Polarizing filters have the property of transmitting light that vibrates in one direction while absorbing light that vibrates in a perpendicular direction. These filters are used extensively in scientific instruments. In sunglasses and when placed over a camera lens, polarizing filters reduce unwanted reflections from…

microscope: Polarizing microscopes: Polarizing microscopes are conventional microscopes with additional features that permit observation under polarized light. The light source of such an instrument is equipped with a polarizing filter, the polarizer, so that the light it supplies is linearly polarized (i.e., the light waves vibrate…

polarography, in analytic chemistry, an electrochemical method of analyzing solutions of reducible or oxidizable substances. It was invented by a Czech chemist, Jaroslav Heyrovský, in 1922. In general, polarography is a technique in which the electric potential (or voltage) is varied in a regular

polarography, in analytic chemistry, an electrochemical method of analyzing solutions of reducible or oxidizable substances. It was invented by a Czech chemist, Jaroslav Heyrovský, in 1922. In general, polarography is a technique in which the electric potential (or voltage) is varied in a regular

light: Sources of polarized light: …materials, the most common being polaroid. Invented by the American physicist Edwin Land, a sheet of polaroid consists of long-chain hydrocarbon molecules aligned in one direction through a heat-treatment process. The molecules preferentially absorb any light with an electric field parallel to the alignment direction. The light emerging from a…

Polaroid Corporation, American manufacturer of cameras, film, and optical equipment founded by Edwin Herbert Land (1909–91), who invented instant photography. The company originated in 1932 as the Land-Wheelwright Laboratories, which Land founded with George Wheelwright to produce Land’s first

Edwin Herbert Land: …a camera (known as the Polaroid Land Camera) that produced a finished print in 60 seconds. The Land photographic process soon found numerous commercial, military, and scientific applications. Many innovations were made in the following years, including the development of a colour process. Land’s Polaroid Land cameras, which were able…

technology of photography: History and evolution: An instant-print colour film (Polacolor) was introduced in 1963 and an integral single-sheet colour film in 1972. After the mid-1970s other manufacturers offered similar instant-print processes. In 1977 Polaroid introduced an 8-mm colour movie film, and in 1982 it introduced still transparency films that permit rapid…

Polaroid Corporation: The company introduced the compact Polaroid SX-70 in 1972. In addition to further technical refinements, the SX-70 combined both negative and positive prints in a single sheet. Instant motion pictures were introduced in 1977.

Douglas Coupland: …essays, and short fiction as Polaroids from the Dead in 1996. In 1998 he published the novel Girlfriend in a Coma and, with Kip Ward, Lara’s Book: Lara Croft and the Tomb Raider Phenomenon, an illustrated tribute to the popularity of the computer game Tomb Raider. Subsequent novels included Miss…

chemical analysis: Amperometry: …the end point in an amperometric titration. An amperometric titration curve is a plot of current as a function of titrant volume. The shape of the curve varies depending on which chemical species (the titrant, the analyte, or the product of the reaction) is electroactive. In each case the curve…

polaron, electron moving through the constituent atoms of a solid material, causing the neighbouring positive charges to shift toward it and the neighbouring negative charges to shift away. This distortion of the regular position of electrical charges constitutes a region of polarization that

radiation: Excitation states: In a polaron state an electron belongs to the association of molecules, but its motion is relatively slow so that it carries with it its own polarization field, which is described as “a cloud of virtual phonons.” A solvated electron (an electron associated with a particular molecule…

Polatsk, city, Vitsyebsk oblast (region), Belarus. It is situated on the Western Dvina River at its confluence with the Polota. Polatsk, first mentioned in 862, has always been a major trading centre and an important fortress with a remarkably stormy history. Modern Polatsk and its satellite town,

Fyodor III: …in Polish and Latin by Simeon Polotsky, a noted theologian who had studied in Kiev and Poland. When Alexis died, Fyodor ascended the throne (Jan. 19 [Jan. 29], 1676), but his youth and poor health prevented him from actively participating in the conduct of government affairs. His uncle Ivan B.…

Ross Poldark, fictional character, the patriarch of the Poldark dynasty in a series of historical novels by Winston Graham. Poldark is an army captain and member of the landed gentry of Cornwall in the late 18th and early 19th centuries. Heroic and temperamental, he struggles to make his tin and

polder, tract of lowland reclaimed from a body of water, often the sea, by the construction of dikes roughly parallel to the shoreline, followed by drainage of the area between the dikes and the natural coastline. Where the land surface is above low-tide level, the water may be drained off through

Arie Poldervaart was a U.S. geologist and petrologist, noted for his work concerning crustal evolution and the petrology of igneous rocks. Poldervaart was a lecturer at the University of Cape Town from 1946 until 1949, when he joined the Bechuanaland Protectorate (now Botswana) Geological Survey;

Museo Poldi Pezzoli, in Milan, museum founded in 1881 in the former private house of Gian Giacomo Poldi Pezzoli, exhibiting his collection of arms and armour from the 14th to the 17th century and Italian paintings from the Renaissance and the 18th century. The museum is also home to antique

Museo Poldi Pezzoli, in Milan, museum founded in 1881 in the former private house of Gian Giacomo Poldi Pezzoli, exhibiting his collection of arms and armour from the 14th to the 17th century and Italian paintings from the Renaissance and the 18th century. The museum is also home to antique

John Bede Polding was the first Roman Catholic bishop in Australia (from 1835), where eight years later he became the first archbishop of Sydney. Polding joined the Benedictine order in 1811 and was ordained priest in 1819. Consecrated a bishop, he arrived at Sydney in 1835. There he divided his

Poland: Ethnic groups: The Polish ethnographic area stretched eastward: in Lithuania, Belarus, and western Ukraine, all of which had a mixed population, Poles predominated not only in the cities but also in numerous rural districts. There were significant Polish minorities in Daugavpils (in Latvia), Minsk (in Belarus), and Kiev…

electric motor: Direct-current commutator motors: …usually have four or more poles to reduce the thickness of the required iron in the stator yoke and to reduce the length of the end connections on the armature coils. These motors may also have additional small poles, or interpoles, placed between the main poles and have coils carrying…

pole construction, Method of building that dates back to the Stone Age. Excavations in Europe show rings of stones that may have braced huts made of wooden poles or weighted down the walls of tents made of animal skins supported by central poles. Two types of Native American pole structures were

Asia: Continental climate: …zone of lowest temperature—a so-called cold pole—is found in the northeast, near Verkhoyansk and Oymyakon, where temperatures as low as −90 °F (−68 °C) and −96 °F (−71 °C), respectively, have been recorded.

Pole of Inaccessibility, point on the Antarctic continent that is farthest, in all directions, from the surrounding seas, lying on the Polar Plateau in a vast territory claimed by Australia. The site, at an elevation of 12,198 feet (3,718 m) above sea level, is occupied by a meteorological research

Theodor Woldsen Storm: …works are the charming story Pole Poppenspäler (1874), the historical novella Aquis submersus (1875), and the novella Im Schloss (1861).

electronic vehicle game: Arcade games: Pole Position (1982), created by Namco Limited of Japan and released in the United States by Atari Inc., was the first racing game to become a hit in arcades. The single-player game featured Formula 1 racing cars, 8-bit colour graphics, the race course used at…

polestar, the brightest star that appears nearest to either celestial pole at any particular time. Owing to the precession of the equinoxes, the position of each pole describes a small circle in the sky over a period of 25,772 years. Each of a succession of stars has thus passed near enough to the

pole vault, sport in athletics (track and field) in which an athlete jumps over an obstacle with the aid of a pole. Originally a practical means of clearing objects, such as ditches, brooks, and fences, pole-vaulting for height became a competitive sport in the mid-19th century. An Olympic event

astronomical map: The celestial sphere: …about a northern or southern celestial pole, the projection into space of Earth’s own poles. Equidistant from the two poles is the celestial equator; this great circle is the projection into space of Earth’s Equator.

Henry VII: Yorkist plots: …worried by the treason of Edmund de la Pole, earl of Suffolk, the eldest surviving son of Edward IV’s sister Elizabeth, who fled to the Netherlands (1499) and was supported by Maximilian. Doubtless the plotters were encouraged by the deaths of Henry’s sons in 1500 and 1502 and of his…

magnetic pole, region at each end of a magnet where the external magnetic field is strongest. A bar magnet suspended in Earth’s magnetic field orients itself in a north–south direction. The north-seeking pole of such a magnet, or any similar pole, is called a north magnetic pole. The south-seeking

North Pole, the northern end of Earth’s axis, lying in the Arctic Ocean, about 450 miles (725 km) north of Greenland. This geographic North Pole does not coincide with the magnetic North Pole—to which magnetic compasses point and which in the early 21st century lay north of the Queen Elizabeth

Reginald Pole was an English prelate who broke with King Henry VIII over Henry’s antipapal policies and later became a cardinal and a powerful figure in the government of the Roman Catholic queen Mary Tudor. His father, Sir Richard Pole, was a cousin of King Henry VII, and his mother, Margaret,

Richard de la Pole was the last Yorkist claimant to the English throne. Pole was the youngest son of John de la Pole, 2nd duke of Suffolk (died 1491/92), and Elizabeth, sister to the Yorkist king Edward IV (ruled 1461–70, 1471–83). Since Edward IV’s brother and successor, Richard III, died

South Pole, the southern end of the Earth’s axis, lying in Antarctica, about 300 miles (480 km) south of the Ross Ice Shelf. This geographic South Pole does not coincide with the magnetic South Pole, from which magnetic compasses point and which lies on the Adélie Coast (at about 66°00′ S, 139°06′

William Poel was an English actor, theatre manager, and producer who revolutionized modern Shakespearean production by returning to Elizabethan staging. Poel was reared among the Pre-Raphaelite artists, and as a boy he posed for William Holman Hunt. He early decided to go on the stage. After

William de la Pole, 1st duke of Suffolk was an English military commander and statesman who from 1443 to 1450 dominated the government of the weak king Henry VI (ruled 1422–61 and 1470–71). He was popularly, although probably unjustly, held responsible for England’s defeats in the late stages of

commercial fishing: Pole-and-line fishing: Line fishing at sea is very popular, not only in traditional fisheries with small boats employing a limited number of hooks but also in industrial operations with large vessels or fleets using thousands of hooks.

curricle, open, two-wheeled gentleman’s carriage, popular in England from about 1700 to 1850. It was pulled by two matched horses yoked abreast and was therefore equipped with a pole, rather than shafts. The pole had to be very strong because it both directed the carriage and bore its weight. To