lamp: Modern electrical light sources: By the mid-20th century the atmospheric arc lamp was used chiefly in large-wattage units for searchlights, for projectors calling for a high intensity and concentrated source, and for other special applications requiring small but powerful sources of blue and ultraviolet energy.

planetary boundary layer (PBL), the region of the lower troposphere where Earth’s surface strongly influences temperature, moisture, and wind through the turbulent transfer of air mass. As a result of surface friction, winds in the PBL are usually weaker than above and tend to blow toward areas of

atmospheric brown cloud, a layer of air pollution containing aerosols such as soot or dust that absorb as well as scatter incoming solar radiation, leading to regional and global climatic effects and posing risks to human health and food security. This layer extends from Earth’s surface to an

chemical equator, in Earth’s atmosphere, a boundary region of air extending from Earth’s surface to an altitude of about 8 km (5 miles) that separates heavily polluted air in the Northern Hemisphere from less-polluted air in the Southern Hemisphere. Although the chemical equator appears to follow

atmospheric circulation, any atmospheric flow used to refer to the general circulation of the Earth and regional movements of air around areas of high and low pressure. On average, this circulation corresponds to large-scale wind systems arranged in several east–west belts that encircle the Earth.

convergence and divergence, in meteorology, the accumulation or drawing apart of air, as well as the rate at which each takes place. The terms are usually used to refer specifically to the horizontal inflow (convergence) or outflow (divergence) of air. The convergence of horizontal winds causes air

atmospheric corona, set of one or more coloured rings that sometimes appear close to the Sun or Moon when they are viewed through a thin cloud composed of water droplets. They are caused by the diffraction of light around the edges of the droplets, with each colour being deviated through a slightly

convergence and divergence: divergence, in meteorology, the accumulation or drawing apart of air, as well as the rate at which each takes place. The terms are usually used to refer specifically to the horizontal inflow (convergence) or outflow (divergence) of air. The convergence of horizontal winds causes air…

atmospheric electricity, electrical phenomena that occur in the lower atmosphere, usually the troposphere—e.g., the production, transport, and loss of free electrical charges; the change in electrical potential from point to point in the atmosphere; and the atmosphere’s electrical conductivity. The

scientific modeling: …model of note is the general circulation model, which is used for simulating human- and non-human-induced climate change. Modeling of geologic events, such as convection within Earth and theoretical movements of Earth’s plates, has advanced scientists’ knowledge of volcanoes and earthquakes and of the evolution of Earth’s surface. In ecology,…

humidity, the amount of water vapour in the air. It is the most variable characteristic of the atmosphere and constitutes a major factor in climate and weather. A brief treatment of humidity follows. For full treatment, see climate: Atmospheric humidity and precipitation. Atmospheric water vapour

Solar Dynamics Observatory: …and Magnetic Imager (HMI), the Atmospheric Imaging Assembly (AIA), and the Extreme Ultraviolet Variability Experiment (EVE). HMI studies changes in the Sun’s magnetic field by capturing images of the Sun in polarized light every 50 seconds. AIA observes the solar corona in eight wavelengths of ultraviolet light every 10 seconds.…

Kathryn Sullivan: …the payload commander of the Atmospheric Laboratory for Applications and Science, a laboratory on a pallet housed in the space shuttle Atlantis’s cargo bay that contained 12 experiments studying Earth’s atmosphere.

Ellen Ochoa: …performed various experiments collectively called ATLAS-2 (Atmospheric Laboratory for Applications and Science-2) that studied the Sun and its interaction with Earth’s atmosphere. The crew also released the SPARTAN satellite, which studied the solar wind for two days before it was retrieved. She was part of the STS-66 Atlantis mission in…

Ellen Ochoa: STS-66 carried the ATLAS-3, which reflew experiments Ochoa had worked with on her previous flight. Another small satellite, CRISTA-SPAS, was released, which studied Earth’s atmosphere for eight days before being retrieved.

numerical analysis: Applications: Another important application is atmospheric modeling. In addition to improving weather forecasts, such models are crucial for understanding the possible effects of human activities on the Earth’s climate. In order to create a useful model, many variables must be introduced. Fundamental among these are the velocity V(x, y, z,…

atmospheric optics, study of optical characteristics and phenomena associated with the interaction of visible sunlight with atmospheric gases, particulates, and water vapour. Refraction, diffraction, Rayleigh scattering (qq.v.), and polarization of light are within the compass of atmospheric

Particulate matter is a type of air pollution that consists of airborne suspensions of extremely small solid or liquid particles, such as soot, dust, smokes, fumes, and mists. Particulate matter—especially those particulates less than 10 micrometers (μm; millionths of a meter) in diameter—are

aerial perspective, method of creating the illusion of depth, or recession, in a painting or drawing by modulating colour to simulate changes effected by the atmosphere on the colours of things seen at a distance. Although the use of aerial perspective has been known since antiquity, Leonardo da

air pollution, release into the atmosphere of various gases, finely divided solids, or finely dispersed liquid aerosols at rates that exceed the natural capacity of the environment to dissipate and dilute or absorb them. These substances may reach concentrations in the air that cause undesirable

atmospheric pressure, force per unit area exerted by an atmospheric column (that is, the entire body of air above the specified area). Atmospheric pressure can be measured with a mercury barometer (hence the commonly used synonym barometric pressure), which indicates the height of a column of

telecommunications media: Radio-wave propagation: …a combination of three mechanisms: atmospheric wave propagation, surface wave propagation, and reflected wave propagation. They are described below.

atmospheric refraction, change in the direction of propagation of electromagnetic radiation or sound waves in traversing the atmosphere. Such changes are caused by gradients in the density of the air. See

World Meteorological Organization: …including global warming; and the Atmospheric Research and Environment Programme, which was designed to promote research on issues such as ozone depletion.

atmospheric river, any long, narrow, and concentrated horizontal corridor of moisture in Earth’s troposphere. Such formations transport vast amounts of water vapor—at flow rates more than double that of the Amazon River—and heat from tropical regions near the Equator toward the middle and higher

space weather: Atmospheric satellite drag: Though the uppermost layer of Earth’s atmosphere, the thermosphere, is extremely tenuous compared with the dense lower layer at the surface, it is not a perfect vacuum. Indeed, the density of the gas a few hundred kilometres above Earth’s surface is appreciable…

telecommunications media: The free-space channel: …beam divergence, atmospheric absorption, and atmospheric scattering. Beam divergence can be minimized by collimating (making parallel) the transmitted light into a coherent narrow beam by using a laser light source for a transmitter. Atmospheric absorption losses can be minimized by choosing transmission wavelengths that lie in one of the low-loss…

atmospheric science, interdisciplinary field of study that combines the components of physics and chemistry that focus on the structure and dynamics of Earth’s atmosphere. Mathematical tools, such as differential equations and vector analysis, and computer systems are used to evaluate the physical

seeing, in astronomy, sharpness of a telescopic image. Seeing is dependent upon the degree of turbulence in the Earth’s atmosphere for a given telescope. Scintillation, the “twinkling” of stars to the unaided eye, is a commonly known result of turbulence in the higher reaches of the atmosphere.

tide: Atmospheric and other tides: Atmospheric tides are detectable meteorological phenomena but are a comparatively minor component in atmospheric motions. An Earth tide differs from oceanic and atmospheric ones in that the response to it is an elastic deformation rather than a flow. Observations of Earth tides contribute to knowledge…

atmospheric turbulence, small-scale, irregular air motions characterized by winds that vary in speed and direction. Turbulence is important because it mixes and churns the atmosphere and causes water vapour, smoke, and other substances, as well as energy, to become distributed both vertically and

telecommunications media: Radio-wave propagation: …a combination of three mechanisms: atmospheric wave propagation, surface wave propagation, and reflected wave propagation. They are described below.

Madrid train bombings of 2004: …four trains in and around Atocha Station in the city’s centre, leaving 191 dead and more than 1,800 injured. Occurring just three days before Spain’s general elections, the attacks had major political consequences.

atole, a hot Mexican beverage typically made from masa (corn dough) or masa harina (dough flour), water, and spices. Sometimes it is made with oatmeal, rice, barley, or wheat instead of masa. The drink is commonly prepared by toasting the masa on a griddle before mixing in water, sugar, vanilla,

atole, a hot Mexican beverage typically made from masa (corn dough) or masa harina (dough flour), water, and spices. Sometimes it is made with oatmeal, rice, barley, or wheat instead of masa. The drink is commonly prepared by toasting the masa on a griddle before mixing in water, sugar, vanilla,

St. Nuno Álvares Pereira: …defeated the Castilians in the Battle of Atoleiros (April 6, 1384). Further brilliant and heroic actions as a field commander won him the office of constable of the kingdom in 1385.

atoll, coral reef enclosing a lagoon. Atolls consist of ribbons of reef that may not always be circular but whose broad configuration is a closed shape up to dozens of kilometres across, enclosing a lagoon that may be approximately 50 metres (160 feet) deep or more. Most of the reef itself is a

rocket and missile system: Air-to-air: …primitive semiactive radar missile, the AA-2 Atoll, an infrared missile closely modeled after the Sidewinder, and the AA-3 Anab, a long-range, semiactive radar-homing missile carried by air-defense fighters. The AA-5 Ash was a large, medium-range radar-guided missile, while the AA-6 Acrid was similar to the Anab but larger and with…

atom, the basic building block of all matter and chemistry. Atoms can combine with other atoms to form molecules but cannot be divided into smaller parts by ordinary chemical processes. Most of the atom is empty space. The rest consists of three basic types of subatomic particles: protons,

atomic bomb, weapon with great explosive power that results from the sudden release of energy upon the splitting, or fission, of the nuclei of a heavy element such as plutonium or uranium. When a neutron strikes the nucleus of an atom of the isotopes uranium-235 or plutonium-239, it causes that

spectroscopy: Noble gas detection: …the chance that a krypton atom will be in the laser beam when the beam is pulsed through the apparatus. The atom buncher consists of a surface held near the temperature of liquid helium to condense the krypton atoms and another pulsed laser to heat the surface just prior to…

green chemistry: Atom economy: Of these principles, “atom economy,” originally suggested by American chemist Barry Trost in 1973, became a central concept among green chemistry researchers. Atom economy was designed to overcome the limitations of the traditional concept of “yield,” the amount of final products, which was…

David Gilmour: Pink Floyd years: …released thematic albums such as Atom Heart Mother (1970), Meddle (1971), and its breakthrough record, The Dark Side of the Moon (1973)—which spent almost 19 years on the Billboard Top 200 album chart and ranked number 55 on Rolling Stone’s list of top 500 albums of all time. The magazine…

atomic physics: …trap to form an “atom laser” analogous to the coherent beam of photons in a conventional laser. The atom laser is still in an early stage of development, but it has the potential to become a key element of future technologies for the fabrication of microelectronic and other nanoscale…

Henry Moore: Later years of Henry Moore: Although the University of Chicago’s Atom Piece, with its mushroom-cloud formation at the top, commemorates the splitting of the atom, the sculpture is also closely related to other large abstract sculptures of the 1960s: Knife-Edge Two-Piece (1962), Locking Piece (1963–64), Three-Way Piece No. 1: Points (1964), and Three-Piece Sculpture No.…

field-emission microscope: …the field-ion microscope is the atom probe. In this instrument, individual atoms are removed from the tip by pulsing the electric field. The atoms pass through a time-of-flight spectrometer, which measures their energy and charge-to-mass ratio. In this way the chemical nature of each atom in the field-ion image may…

chemical bonding: Hypervalence: …more atoms attached to a central atom than can be accommodated by an octet of electrons. An example is sulfur hexafluoride, SF6, for which writing a Lewis structure with six S―F bonds requires that at least 12 electrons be present around the sulfur atom:

the Atom, American comic strip superhero created for DC Comics by writer Bill O’Connor and artist Ben Flinton. The character first appeared in All-American Comics no. 19 (October 1940). Al Pratt, the first hero to adopt the mantle of the Atom, was a college student tired of being teased about his

Karl Jaspers: Postwar development of thought: …die Zukunft des Menschen (The Future of Mankind, 1961). The aim of this political world union would not be absolute sovereignty but rather world confederation, in which the various entities could live and communicate in freedom and peace.

material culture: …beginning of the third great revolution in material culture and culture as a whole.

cannon: …shells; it was called an atomic cannon. Similar weapons were displayed by the U.S.S.R. in 1957. In later years, atomic explosives were fitted into shells small enough to be fired in standard artillery. See artillery.

industrial glass: Science in glassmaking: Zachariasen published The Atomic Arrangement in Glass, a classic paper that had perhaps the most influence of any published work on glass science. Zachariasen’s work placed the understanding of glass structure and its relationship to composition on its modern footing. The principles of his atomic structure theory…

spectroscopy: Methods: …his collaborators, using molecular and atomic beams. A beam focused by magnets in the absence of a radio-frequency field was defocused and lost when atoms were induced to make transitions to other states. The radio-frequency or microwave spectrum was taken by measuring the number of atoms that remained focused in…

John Goodman: Film career: …a Time in Venice, and Atomic Blonde. His later movies included Captive State (2019), in which aliens have colonized Earth and face a resistance movement.

atomic bomb, weapon with great explosive power that results from the sudden release of energy upon the splitting, or fission, of the nuclei of a heavy element such as plutonium or uranium. When a neutron strikes the nucleus of an atom of the isotopes uranium-235 or plutonium-239, it causes that

Hiroshima: …Casualty Commission (since 1975 the Radiation Effects Research Foundation) began to conduct medical and biological research on the effects of radiation in Hiroshima. A number of public hospitals and private clinics give free treatment to victims of the atomic bombing (hibakusha). Hiroshima Castle, destroyed in the bombing, was restored in…

Hiroshima Peace Memorial, ruins of a building that was destroyed by an atomic bomb in Hiroshima, Japan, and that is preserved as a memorial to those killed and as a reminder. At 8:15 AM on August 6, 1945, the U.S. B-29 bomber Enola Gay dropped the world’s first atomic bomb used in war on the city

atomic bombings of Hiroshima and Nagasaki, during World War II, American bombing raids on the Japanese cities of Hiroshima (August 6, 1945) and Nagasaki (August 9, 1945) that marked the first use of atomic weapons in war. Tens of thousands were killed in the initial explosions and many more would

cannon: …shells; it was called an atomic cannon. Similar weapons were displayed by the U.S.S.R. in 1957. In later years, atomic explosives were fitted into shells small enough to be fired in standard artillery. See artillery.

atomic clock, type of clock that uses certain resonance frequencies of atoms (usually cesium or rubidium) to keep time with extreme accuracy. The electronic components of atomic clocks are regulated by the frequency of the microwave electromagnetic radiation. Only when this radiation is maintained

superfluidity: Theoretical explanation of superfluidity: …for example, the phenomenon of atomic diamagnetism. Similarly, a single atom (or molecule) placed in a ring-shaped container is allowed by quantum mechanics to travel around the ring with only certain definite velocities, including zero. In an ordinary liquid such as water, the thermal disorder ensures that the atoms (or…

chemical analysis: Luminescence: …emitted radiation, the method is atomic emission spectrometry. If a chemical reaction is used to initiate the luminescence, the technique is chemiluminescence; if an electrochemical reaction causes the luminescence, it is electrochemiluminescence.

nuclear energy, energy that is released in significant amounts in processes that affect atomic nuclei, the dense cores of atoms. It is distinct from the energy of other atomic phenomena such as ordinary chemical reactions, which involve only the orbital electrons of atoms. One method of releasing

nuclear weapon: Origins of the Super: The Atomic Energy Act, signed by President Truman on August 1, 1946, established the Atomic Energy Commission (AEC), replacing the Manhattan Engineer District, and gave it civilian authority over all aspects of atomic energy, including oversight of nuclear warhead research, development, testing, and production.

Atomic Energy Commission, U.S. federal civilian agency established by the Atomic Energy Act, which was signed into law by President Harry S. Truman on Aug. 1, 1946, to control the development and production of nuclear weapons and to direct the research and development of peaceful uses of nuclear

Vikram Sarabhai: …was appointed chairman of the Atomic Energy Commission of India. Carrying forward Bhabha’s work in the field of nuclear research, Sarabhai was largely responsible for the establishment and development of India’s nuclear power plants. He laid the foundations for the indigenous development of nuclear technology for defense purposes.

nuclear weapon: France: …October 18, 1945, the French Atomic Energy Commission (Commissariat à l’Énergie Atomique; CEA) was established by Gen. Charles de Gaulle with the objective of exploiting the scientific, industrial, and military potential of atomic energy. The military application of atomic energy did not begin until 1951. In July 1952 the National…

United Nations: Arms control and disarmament: …Assembly in 1946 created the Atomic Energy Commission to assist in the urgent consideration of the control of atomic energy and in the reduction of atomic weapons. The United States promoted the Baruch Plan, which proposed the elimination of existing stockpiles of atomic bombs only after a system of international…

Iran: Power: The Atomic Energy Organization (AEO) of Iran was established in 1973 to construct a network of more than 20 nuclear power plants. By 1978 two 1,200-megawatt reactors near Būshehr on the Persian Gulf were near completion and were scheduled to begin operation early in 1980, but…

Logical Atomism: …(an atomic proposition) and an atomic fact; thus, for each atomic fact there is a corresponding atomic proposition. An atomic proposition is one that asserts that a certain thing has a certain quality (e.g.: “This is red.”). An atomic fact is the simplest kind of fact and consists in the…

nuclear fission, subdivision of a heavy atomic nucleus, such as that of uranium or plutonium, into two fragments of roughly equal mass. The process is accompanied by the release of a large amount of energy. In nuclear fission the nucleus of an atom breaks up into two lighter nuclei. The process may

chemical analysis: Luminescence: …gaseous atoms, it is termed atomic fluorescence.

spectrochemical analysis: Atomic fluorescence spectrometry makes use of the same basic instrumental components as atomic absorption spectrometry; however, it measures the intensity of the light emitted by atoms that have been excited from their ground state by the absorption of light of shorter wavelength than that emitted.…

spectrochemical analysis: Atomic fluorescence spectrometry makes use of the same basic instrumental components as atomic absorption spectrometry; however, it measures the intensity of the light emitted by atoms that have been excited from their ground state by the absorption of light of shorter wavelength than that emitted.…

surface analysis: Atomic force microscopy: Atomic force microscopy profiles a sample by dragging an atomically sharp (i.e., only a few atoms wide) stylus across the surface and measuring the force between the stylus and the surface. The resulting signal can be translated into a description of the…

Stanislao Cannizzaro: A single system of atomic formulas: In his 1858 pamphlet, Cannizzaro showed that a complete return to the ideas of Avogadro could be used to construct a consistent and robust theoretical structure that fit nearly all of the available empirical evidence. The few remaining anomalies, he argued, could easily…

nuclear fusion, process by which nuclear reactions between light elements form heavier elements (up to iron). In cases where the interacting nuclei belong to elements with low atomic numbers (e.g., hydrogen [atomic number 1] or its isotopes deuterium and tritium), substantial amounts of energy are

maser: Gas masers: …frequency or time is the atomic hydrogen maser introduced by American scientists N.F. Ramsey, H.M. Goldenberg, and D. Kleppner in 1960. Its output is a radio wave whose frequency of 1,420,405,751.786 hertz (cycles per second) is reproducible with an accuracy of one part in 30 × 1012. A clock controlled…

atomism, any doctrine that explains complex phenomena in terms of aggregates of fixed particles or units. This philosophy has found its most successful application in natural science: according to the atomistic view, the material universe is composed of minute particles, which are considered to be

epitaxy: Atomic layer epitaxy is based on introducing one gas that will absorb only a single atomic layer on the surface and following it with another gas that reacts with the preceding layer.

atomic mass, the quantity of matter contained in an atom of an element. The observed atomic mass is slightly less than the sum of the mass of the protons, neutrons, and electrons that make up the atom. The difference, called the mass defect, is accounted for during the combination of these

mass number, in nuclear physics, the sum of the numbers of protons and neutrons present in the nucleus of an atom. The mass number is commonly cited in distinguishing among the isotopes of an element, all of which have the same atomic number (number of protons) and are represented by the same

atomic mass unit (AMU), in physics and chemistry, a unit for expressing masses of atoms, molecules, or subatomic particles. An atomic mass unit is equal to 1 12 the mass of a single atom of carbon-12, the most abundant isotope of carbon, or 1.660538921 × 10 −24 gram. The mass of an atom consists of

atomic model, in physics, a model used to describe the structure and makeup of an atom. Atomic models have gone through many changes over time, evolving as necessary to fit experimental data. For a more in-depth discussion of the history of atomic models, see atom: development of atomic theory.

atom: Bohr’s shell model: …to the orientation of their magnetic moments. In their experiment Stern and Gerlach found only two deflections, not the continuous distribution of deflections that would have been seen if the magnetic moment had been oriented in any direction. Thus, it was determined that the magnetic moment and the angular momentum…

atom: The nucleus: The primary constituents of the nucleus are the proton and the neutron, which have approximately equal mass and are much more massive than the electron. For reference, the accepted mass of the proton is 1.672621777 × 10−24 gram, while that of the…

atomic number, the number of a chemical element in the periodic system and on the periodic table that equals the number of protons in the nucleus of the atom. The elements are arranged on the table in order of increasing number of protons in the nucleus. Accordingly, the number of protons, which is

orbital, in chemistry and physics, a mathematical expression, called a wave function, that describes properties characteristic of no more than two electrons in the vicinity of an atomic nucleus or of a system of nuclei as in a molecule. An orbital often is depicted as a three-dimensional region

particle accelerator: …beam of fast-moving, electrically charged atomic or subatomic particles. Physicists use accelerators in fundamental research on the structure of nuclei, the nature of nuclear forces, and the properties of nuclei not found in nature, as in the transuranium elements and other unstable elements. Accelerators are also used for radioisotope production,…

atomic physics, the scientific study of the structure of the atom, its energy states, and its interactions with other particles and with electric and magnetic fields. Atomic physics has proved to be a spectacularly successful application of quantum mechanics, which is one of the cornerstones of

liquid: Speed of sound and electric properties: The second effect, atomic polarization, arises because there is a relative change in the mean positions of the atomic nuclei within the molecules. This generally small effect is observed at radio frequencies but not at optical, and so it is missing from the refractive index. The third effect,…

nuclear energy, energy that is released in significant amounts in processes that affect atomic nuclei, the dense cores of atoms. It is distinct from the energy of other atomic phenomena such as ordinary chemical reactions, which involve only the orbital electrons of atoms. One method of releasing

Logical Atomism: …an “atom” of language (an atomic proposition) and an atomic fact; thus, for each atomic fact there is a corresponding atomic proposition. An atomic proposition is one that asserts that a certain thing has a certain quality (e.g.: “This is red.”). An atomic fact is the simplest kind of fact…

atomic radius, half the distance between the nuclei of identical neighbouring atoms in the solid form of an element. An atom has no rigid spherical boundary, but it may be thought of as a tiny, dense positive nucleus surrounded by a diffuse negative cloud of electrons. The value of atomic radii

Manhattan Project, U.S. government research project (1942–45) that produced the first atomic bombs. See Britannica’s interactive timeline of the Manhattan Project. American scientists, many of them refugees from fascist regimes in Europe, took steps in 1939 to organize a project to exploit the

Emerson, Lake & Palmer: … (1968–69); and Palmer had cofounded Atomic Rooster (1969–70). ELP made synthesizer keyboards rather than guitars the centrepiece of its sound and developed an eclectic and innovative style blending classical music, jazz, blues, electronic music (then still a novelty), and

Harrison Brown: …editor in chief for the Bulletin of the Atomic Scientists from 1985 until his death.

spectroscopy: Methods: One second is defined as the time it takes for the cesium frequency to oscillate 9,192,631,770 times. Such atomic clocks have a longer-term uncertainty in their frequency that is less than one part in 1013. Measurement of time intervals based on the cesium atom’s oscillations are…

metalogic: Syntax and semantics: …as forming the simple (atomic) sentences, and (3) a set of inductive clauses—inductive inasmuch as they stipulate that natural combinations of given sentences formed by such logical connectives as the disjunction “or,” which is symbolized “∨”; “not,” symbolized “∼”; and “for all ,” symbolized “(∀),” are again sentences. [“(∀)”…

atomic radius, half the distance between the nuclei of identical neighbouring atoms in the solid form of an element. An atom has no rigid spherical boundary, but it may be thought of as a tiny, dense positive nucleus surrounded by a diffuse negative cloud of electrons. The value of atomic radii