An Etymological Dictionary of Astronomy and Astrophysics

In the Johnson → UBV system,
a reddening-free parameter which is related to the → effective temperature of stars and thus
provides a useful, but rough, discriminant for → spectral types.
It is expressed as: Q = (U - B) - 0.72 (B - V).

See also: → index.

A two-dimensional figure that consists of four points connected by straight lines. Same as → tetragon; see also → quadrilateral.

Etymology (EN): L.L. quadrangulum, noun use of neuter of L. quadrangulus, quadriangulus “four-cornered,” from quadr- variant of quadri- before a vowel “four,” akin to quattuor, → four, cognate with Pers. cahâr, as below; → angle.

Etymology (PE): Cahârgušé, cârguš “four-cornered,” from cahâr, câr “four,” cognate with L. quattuor, → four,

• gušé, guš “corner, angle;” Mid.Pers. gôšak “corner.”

An obsolete → constellation created by the French astronomer Jérôme Lalande in 1795. He named it such for the main astronomical instrument, that is → mural quadrant, he used. Quadrans Muralis was located between the constellations → Boötes and → Draco. The name disappeared from astronomical catalogs, but the → meteor shower→ Quadrantids has kept that name.

See also: → mural quadrant.

1. A quarter of a circle; an arc of 90°.
   
2. Any of the four parts into which a plane is divided by a pair of rectangular axes.
   
3. An instrument, usually containing a graduated arc of 90°, formerly used in astronomy and navigation to measure the angles and altitudes of stars. → mural quadrant.

Etymology (EN): M.E., from L. quadrantem (nominative quadrans) “fourth part.”

Etymology (PE): Cârakân, from cârak + -ân.
Cârak “quarter,” literally “fourth, a fourth part of one,” from câr, variant of cahâr, → four, cognate with L. quattuor, + -ak, contraction of yak “one,”
from Mid.Pers. êwak (Proto-Iranian *aiua-ka-); O.Pers. aiva- “one, alone;” Av. aēuua- “one, alone” (cf. Skt. éka- “one, alone, single;” Gk. oios “alone, lonely;” L. unus “one;” E. one); -ân nuance suffix.

An annual → meteor shower reaching a peak about 3 January and having its → radiant in the constellation → Boötes.

See also: From L. Quadrant-, from Quadrans Muralis , → mural quadrant.

Of or relating to or resembling a → square.
Of, relating to, or containing terms with powers no higher than the power of two.

Etymology (EN): Quadratic, adj. of quadrate, from L. quadratus p.p. of quadrare “to make square.”

Etymology (PE): Câruši pertaining to
câruš “square,” from Av. caθruša- “four sides (of a four-sided figure),”
from caθru- “four,” Mod.Pers. cahâr, câr “four,” cognate with L. quattuor, → four.

An equation with the general form of ax² + bx +c = 0, in which the highest power of the unknown is the second power (square).

See also: → quadratic; → equation.

A formula relating the unknown part of a → quadratic equation (the roots of the equation, x) to the known parts (a, b, and c): x = (-b&plusmn (b² - 4ac)^½) / 2a.

See also: → quadratic; → formula.

1. General: The process of making something square; the act of squaring.
   
2. Math.: The act or process of constructing a → square with an area equal to that of a specified surface, especially a surface bounded by a curve.
   
3. Astro.: The position of a planet or the Moon when it makes a 90° angle with the Sun as seen from Earth.

Etymology (EN): From L. quadratura, from quadrat(us) p.p. of quadrare “to make square.”

Etymology (PE): 1) Cârušeš verbal noun of cârušidan “to square,” from câruš “square,” from Av. caθruša-, → quadratic.
Câruši quality noun of câruš “square,” as preceding.

2. Navadân, from navad “ninety,” referring to the longitude difference of 90° (Mid.Pers. nawad; Av. nauuaiti- “ninety,” from nauua- “nine” (Mod.Pers. noh); cf. Skt. navati- “ninety”) + -ân suffix of place and time.

Constructing a square whose area equals that of a given circle. This was one of the three geometric problems of antiquity. It was finally proved to be an impossible problem when π was proven to be transcendental
by Lindemann in 1882. Same as → squaring the circle.

See also: → quadrature; → circle.

A plane figure bounded by four straight lines.

See also: From L. quadrilater(us) “four-sided,” from L. quattuor, → four, + → lateral.

Fourfold; consisting of four parts.

Etymology (EN): M.E. from L. quadruplus, from quadru-

• duple, from duplus, from du(o) “two” + -plus “fold.”

Etymology (PE): Cahârtâ, from cahâr, → four, cognate with L. quattuor, + tâ “fold, plait, ply; piece, part” (Mid.Pers. tâg “piece, part”).

A stellar system consisting of four stars orbiting around a common → center of mass.

See also: → quadruple; → system.

Of or pertaining to a → quadrupole, especially a → quadrupole moment.

See also: → quadrupole + -ar, → -al.

A set of either two → electric dipoles or two → magnetic dipoles in close proximity to each other arranged with alternating polarities and acting as a single unit. Quadrupole interactions are much smaller than dipole interactions, but can allow transitions forbidden in dipole moment transitions.

Etymology (EN): From L. quadru-, variant of quadri- “four” + → pole, on the model of → dipole.

Etymology (PE): Cahâr, → four, + qotb, → pole + noun/nuance suffix -é.

The → anisotropy which is at the origin of the → cosmic microwave background polarization. The quadrupole anisotropy could arise from three types of perturbations: → scalar perturbation, → vector perturbation, and → tensor perturbation

See also: → quadrupole; → anisotropy.

A device, consisting of four → electrodes or → magnetic poles arranged in alternating → polarity, that focuses a beam of → charged particles.

See also: → quadrupole; → lens.

A quantity characterizing an electric charge distribution, determined by the product of the charge density, the second power of the distance from the origin, and a spherical harmonic over the charge distribution.

See also: → quadrupole; → moment.

1. To shake or tremble.
   

2. The act or an instance of quaking. → earthquake, → starquake.

Etymology (EN): M.E., from O.E. cwacian “to shake, tremble,” of unknown origin.

Etymology (PE): Larzidan, larz “to tremble, shiver,” → seismo-.

1. A quality, accomplishment, etc., that fits a person for some function, office, or the like.
   

   2. A circumstance or condition required by law or custom for getting, having, or exercising a right, holding an office, or the like.
      

   3. The act of qualifying; state of being qualified (Dictionary.com).

See also: → qualify; → -tion.

Having the qualities, accomplishments, etc., that fit a person for some function, office, or the like (Dictionary.com).

See also: Past participle of → qualify.

1. Be entitled to a particular benefit or privilege by fulfilling a necessary condition; become officially recognized as a practitioner of a particular profession or activity, typically by undertaking a course and passing examinations.
   

   2. Officially recognize or establish (someone) as a practitioner of a particular profession or activity (OxfordDictionaries.com).

See also: → quality; → -fy.

Pertaining to or concerned with quality or qualities.

Etymology (EN): From L.L. qualitativus, from qualitat- + -ivus, → -ive.

Etymology (PE): Cunik, from cuni, → quality, + -ik, → -ic.

A distinguishing characteristic, property, or attribute of something.

2. → image quality.
   

3. → sound quality.

Etymology (EN): M.E. qualite, from O.Fr. qualite (Fr. qualité), from L. qualitas, from qual(is) “of what sort?” + → -ity.

Etymology (PE): Cunâ, cuni, from Mid.Pers. cigôn “how?,” cigônêh “nature, character,” O.Pers/Av. ci- “what, any,” collateral stem to ka- “who?, what?” (cf. Skt. ka-; Gk. po-; L. quo-; E. what, who; PIE *qwos/*qwes) + Av. gaona- “color” (Mid.Pers. gônak “kind, species”).

Plural of → quantum.

Etymology (EN): L. plural of quantum.

Etymology (PE): Kuântomhâ, from kuântom, → quantum + -hâ plural suffix.

The fact or process of quantifying.

See also: Verbal noun of → quantify.

1. 1. A word that indicates the quantity of something.
      

2. Math.: A phrase in a logical expression that somehow specifies the quantity of variables. In particular either of the phrases “for all” (written symbolically as ∀) and “there exists” (∃).
   

3. In → predicate logic, a symbol that applies to, or binds, → variables which represent the → arguments of → predicates. See also → existential quantifier and → universal quantifier. In → first-order logic theses variables must range over → individuals. In higher-order logics they may range over predicates.

See also: Agent noun of → quantify

1. To express as a number or amount.
   

2. In predicate logic: To express by a → symbol how many of the → individuals have the property in common.

Etymology (EN): M.L. quantificare, from to L. quant(us) “how much?” + -ificare “-ify.”

Etymology (PE): Candâyidan infinitive of candâ, → quantity

• -idan.

Relating to, measuring, or measured by the quantity of something rather than its → quality (OxfordDictionaries.com).

See also: From L.L. quantitativus, from quanitat- + -ivus “-ive.”

The analysis of a chemical sample to derive its precise percentage composition in terms of elements, radicals, or compounds.

See also: → quantitative; → analysis.

The property of magnitude.
An entity having magnitude, size, extent, or amount.

Etymology (EN): M.E., from rom O.Fr. quantite (Fr. quantité), from L. quantitatem (nominative quantitas), from quant(us) “how much?” + -itas, → -ity.

Etymology (PE): Candâ, candi “quantity,” Mid.Pers. candih “amount, quantity,” from cand “how many, how much; so many, much;” O.Pers. yāvā “as long as;” Av. yauuant- [adj.] “how great?, how much?, how many?,” yauuat [adv.] “as much as, as far as;” cf. Skt. yāvant- “how big, how much;” Gk. heos “as long as, until.”

1. The procedure of restricting a continuous quantity to certain discrete values.
   
2. Physics: The procedure of deriving the quantum-mechanical laws of a system from its corresponding classical laws.

See also: Verbal noun of → quantize.

Math.: To restrict a variable quantity to discrete values rather than to a continuous set of values.
Physics: To change the description of a physical system from classical to quantum-mechanical, usually resulting in discrete values for observable quantities, as energy or angular momentum.

Etymology (EN): From quant(um) + → -ize.

Etymology (PE): From kuântom, → quantum, + -idan infinitive suffix.

1. Capable of existing in only one of several states.
   

2. Of or pertaining to discrete values for → observable quantities.

See also: P.p. of → quantize.

A device with a limited number of possible output values hat can translate an incoming signal into these values or codes for outputting.

See also: Agent noun of → quantize.

The smallest amount of energy that can be absorbed or radiated by matter at a specified frequency (plural quanta). It is a → discrete quantity of energy hν associated with a wave of frequency ν, where h represents the
→ Planck’s constant.

See also: Quantum “a particular amount,” from L. quantum “how much,” neuter singular of quantus “how great.” Introduced in physics by Max Planck (1858-1947) in 1900.

A concept whereby properties of objects vary according to the energy with which they are probed. An atomic system in its → ground state tends to remain as it is if little energy is fed in, betraying no evidence of its internal structure. Only when it is excited into a higher state do complexities emerge. This is the essence of quantum censorship. Thus, below an energy threshold, atoms appear to be impenetrable. Above it, their components can be exposed (F. Wilczek, 2013, Nature 498, 31).

Etymology (EN): → quantum; censorship, from censor,
from M.Fr. censor and directly from L. censor “a Romain magistrate who kept the register or census of the citizens, and supervised morals,” from censere “to appraise, value, judge,” from PIE root *kens- “to speak solemnly, announce;” cf. Av. səngh- (sanh-) “to declare, explain;” Pers. soxan “word, speech;” Skt. śams- “to praise, recite.”

The → quantum field theory that deals with the → strong interaction and the structure of elementary particles in the framework of → quantum theory. The cohesive attraction between the → quarks, that constitute → hadrons, involves the participation of three particles. Each of these particles is assigned a different → color “charge.” The existence of these “charges” requires a multiplicity of different messenger particles to communicate the interaction and glue the quarks together. These messengers are called → gluons and there are eight different types.

See also: → quantum; → chromodynamics

In quantum physics, a situation where an object’s wave property is split in two, and the two waves coherently interfere with each other in such a way as to form a single state that is a superposition of the two states.

This phenomenon is based on the fact that atomic particles have wave-like properties.

Quantum coherence is in many ways similar to → quantum entanglement, which involves the shared states of two quantum particles instead of two quantum waves of a single particle.

Quantum coherence and quantum entanglement are both rooted in the → superposition principle.

See also: → quantum; → coherence.

A type of computer, as yet hypothetical, that uses quantum mechanical laws, such as the → superposition principle and the → quantum entanglement, to perform calculations based on the behavior of particles at the → subatomic level. A quantum computer would gain enormous processing power through the ability to be in multiple states, and to perform tasks using all possible permutations simultaneously.

See also: → quantum; → computer.

Of an atomic energy level, the difference between the principal quantum number and the effective quantum number.

See also: → quantum; → defect.

In a detector, the ratio of the number of photoelectrons released to the number of incident photons at a specific wavelength.

See also: → quantum; → efficiency.

The → quantum field theory that describes the properties of → electromagnetic radiation and its interaction with electrically charged matter in the framework of → quantum theory.

See also: → quantum; → electrodynamics.

A quantum → phenomenon that occurs when two or more particles (→ photons or → atomic particles) that have a common origin remain linked together when they travel apart. A measurement of one of the particles determines not only its → quantum state but the quantum state of the other particle as well. A change in one is instantly reflected in the other.

To use a familiar example, it is as if you have a pair of dice entangled in such a way that when you throw them the sum of the two is 7. Any time you cast them, if the first die shows 2, 5, 3, etc. the other will show 5, 2, 4, etc., respectively.

Quantum entanglement is rooted in the → superposition principle. But, in contrast to → quantum coherence, the states in a superposition are the shared states of two entangled particles rather than those of the two split waves of a single particle.

There are several ways for entangling atomic particles. Photons can be entangled using → cascade transitions, as was done by Alain Aspect and colleagues in the early 1980s (→ Aspect experiment). Calcium atoms are put into a highly-excited energy level where the electron is forbidden to return to the → ground state by emitting a single photon. As a result, the atoms → decay by emitting two photons which are entangled.

Like quantum coherence, quantum entanglement plays an essential role in quantum technologies, such as quantum teleportation, quantum cryptography, and super dense coding. See also → EPR paradox.

See also: → quantum; → entanglement.

The quantum mechanical theory based on the assumption that the interactions between particles and fields are mediated by messenger particles. Accordingly, particles are → quanta of a field, just s photons are quanta of light. All fields display a granular structure in interaction.

QFT is the framework in which quantum mechanics and → special relativity are successfully reconciled (→ Dirac equation). It forms the basis of today’s particle physics.

See also: → quantum; → field;
→ theory.

The temporary variation in a → quantum field due to the → uncertainty principle.

See also: → quantum; → fluctuation.

A theory of gravity, yet to be developed, that would properly include quantum mechanics. Because of the tensor nature of general relativity, it is not renormalizable as a field theory in perturbation from flat space. So far various attempts to quantize general relativity have been unsuccessful.

See also: → quantum; → gravity.

The science concerned with the transmission, storage, and processing of information using quantum mechanical systems. It exploits the notion of → quantum entanglement between systems and joins several fields of knowledge, mainly quantum physics, information, computation, and probability.

See also: → quantum; → information.

The transition of a quantum system from one stationary state to another, accompanied by absorption or emission of energy.

See also: → quantum; → jump.

A → physical system that is specified by a → wave function.

See also: → quantum; → mechanical; → system.

A development of Newtonian mechanics based on the discrete character of energy (Planck 1900) and the wave motion of material particles (de Broglie 1924). It is relies on the consideration that energy state of a quantum mechanical system can be derived at a given instant by a function whose square of the modulus gives the probability distribution of the coordinates of the system. Quantum mechanics is essential for the treatment of all atomic processes. It holds also for ordinary large scale processes although in this case the deviations from Newtonian mechanics are negligible.

See also: → quantum; → mechanics.

A random variation of signal due to fluctuations in the average rate of incidence of quanta on a detector. Quantum noise is described by the → Poisson distribution. Same as → photon noise and → shot effect.

See also: → quantum; → noise.

A number used in quantum mechanics, specifying the state of an electron bound in an atomic system. The quantum numbers are integers or half integers and specify the number of units of energy, momentum, spin, etc. possessed by an electron.

See also: → quantum; → number.

Since → Planck’s constant has the dimension of → energy × → time, its
sometimes called the quantum of → action.

See also: → quantum; → action.

A phase transitions that occurs at zero temperature as a function of a non-thermal parameter like → pressure, → magnetic field, or → chemical composition. In contrast to ordinary → phase transitions, which are associated with passage through a critical temperature, quantum phase transitions are associated with → quantum fluctuations, a consequence of → Heisenberg’s uncertainty principle. For example, see → Bose-Einstein condensation.

See also: → quantum; → phase; → transition.

In → quantum mechanics, the state of a system as described by a set of → quantum numbers and represented by an → eigenfunction.

See also: → quantum; → state.

The theoretical basis of modern physics which describes the behavior and interactions of elementary particles or energy states based on the assumptions that energy is subdivided into discrete amounts and that matter possesses wave properties. → quantum mechanics;
→ quantum field theory.

See also: → quantum; → theory.

A property in → quantum mechanics whereby in a quantum system the sum of all probabilities of all possible outcomes must be 1. Quantum unitarity makes the modulous of a → quantum state invariant with time.

See also: → quantum. → unitary.

A generalization of the classical concept of → random walk using quantum mechanical laws such as the → superposition principle and → interference of quantum amplitudes. In the classical version the particle moves in the position space with a certain probability. In contrast, in the quantum counterpart the particle moves by exploring multiple possible paths simultaneously with the amplitudes corresponding to the influence of different paths.
The concept of quantum walk is studied in two standard forms: → continuous-time quantum walk and → discrete-time quantum walk. Quantum walk was first introduced by Aharonov et al.
(1993, Phys. Rev. A, 48, 1687).

See also: → continuous; → walk.

In photochemistry, the number of defined events which occur per photon absorbed by the system.

See also: → quantum; → theory.

A linear → Hermitian operator associated with a physical quantity.

See also: → quantum; → mechanics;
→ operator.

A faint object (magnitude 18.5), probably a dwarf planet, orbiting the Sun beyond Neptune in the Kuiper belt. Discovered in 2002, Quaoar is estimated to have a diameter of 1260 km and an orbital period of 287 years.

See also: Quaoar the name of a creation deity of the Native American Tongva, located in the Los Angeles area, where the discovery was made.

Any of the hypothetical particles with spin 1/2, baryon number 1/3, and electric charge 1/3 or -2/3 that, together with their antiparticles, are believed to constitute all the elementary particles classed as baryons and mesons. Quarks are distinguished by their flavors, designated as up (u), down (d), strange (s), charm (c), bottom or beauty (b), and top or truth (t), and their colors, red, green, and blue.

The key evidence for the existence of quarks came from a series of inelastic electron-nucleon scattering experiments (→ inelastic scattering) conducted between 1967 and 1973 at the Stanford Linear Accelerator Center. Other theoretical and experimental advances have confirmed this discovery, leading to the → standard model of particle physics.

See also: Quark, coined in 1963 by the American physicist Murray Gell-Mann (1929-), who took it from a nonsense word in James Joyce’s novel Finnegans Wake (1939): Three quarks for Muster Mark! // Sure he has not got much of a bark // And sure any he has it’s all beside the mark.

The phenomenon wherein the → quarks are permanently bound together and can never be removed from the → hadrons they compose.

See also: → quark; → confinement.

A hypothetical star so dense that it is composed of degenerate quarks, a matter
denser than that of a neutron star.

See also: → quark; → star.

A phase transition, predicted by cosmological models, to have occurred at approximately 10^-5 seconds after the Big Bang to convert a plasma of free quarks and gluons into hadron.

See also: → quark; → hadron; → phase; → transition.

A fourth of the Moon’s period or monthly revolution around Earth. → first quarter; → last quarter.

Etymology (EN): from O.Fr. quartier, from L. quartarius “fourth part,” from quartus “fourth,” related to quattuor “four,” cognate with Pers. câr, cahâr, as below.

Etymology (PE): Cârak “quarter,” literally “fourth, a fourth part of one,” from câr, contraction of cahâr, → four,

• -ak, contraction of yak, yek “one.” Yek “one, alone,” from Mid.Pers. êwak (Proto-Iranian *aiua-ka-); O.Pers. aiva- “one, alone;” Av. aēuua- “one, alone;” cf. Skt. éka- “one, alone, single;” Gk. oios “alone, lonely;” L. unus “one;” E. one.

A plate of doubly refracting material cut parallel to the optic axis of the crystal and of such a thickness that a phase difference of 90° is introduced between the ordinary and extraordinary rays for light of a particular wavelength. → half-wave plate.

See also: → quarter; → wave; → plate.

An equation containing unknowns of the fourth power; the general form: ax⁴ + bx³ + cx² + dx + e = 0.

Etymology (EN): From L. quart(us) “fourth” (→ quarter) + → -ic; → equation.

Etymology (PE): hamugeš, → equation; câromân, from cârom “fourth,” from câr, cahâr “four”

• -om “-th” + -ik, → -ic.

In statistics, any of the four groups of a frequency distribution each containing 25% of the total number of individual observations.

Etymology (EN): From M.L. quartilis, from quart(us) “fouth” + -ilis “-ile” a suffix of adjectives expressing capability, susceptibility, liability, aptitude.

Etymology (PE): Cârakvâr, from cârak, → quarter, + -vâr suffix of similarity, size, aptitude.

One of the most abundant → minerals in the Earth’s → crust. Quartz is made up of silicon dioxide (SiO₂), or → silica. It has marked → piezoelectric properties and → dielectric strength.

See also: From Ger. Quarz “rock crystal,” from M.H.G. twarc.

An compact, extragalactic object which is highly luminous and looks like a star. Their redshifts can be large and their brightness varies. Quasars have an intrinsic luminosity which can reach some 100 times that of bright galaxies. They are thought to be active galactic nuclei with a size a little larger than the solar system. The first quasar to be identified as such, in 1963,
was the radio source 3C 273 at a redshift of 0.158. With its 13th magnitude, it is the optically brightest quasar as observed from Earth.
Some quasars are strong radio sources.

Etymology (EN): From quas(i) + (stell)ar (object).

Etymology (PE): Setârevaš, from setâré, → star,

• -vaš, → quasi-.

A prefix meaning “resembling, almost, having some, but not all of the features of.”

Etymology (EN): From L. quasi “as if, as though,” from qua(m)" as" + si “if.”

Etymology (PE): Cunân “so, like that; just as if,” from cun “how?,” (Mid.Pers. cigôn “how?,” cigônêh “nature, character,” O.Pers/Av. ci- “what, any,” collateral stem to ka- “who?, what?;” cf. Skt. ka-; Gk. po-; L. quo-; E. what, who; PIE *qwos/*qwes) + suffix ân. -vaš a suffix of similitude.

A system in which the nuclei of two colliding atoms approach each other closely for a brief lapse of time so that their electrons are arranged in atomic orbitals characteristic of a single atom with combined atomic number.

See also: → quasi-; → atom.

A subsystem if its intrinsic energy is large, on the average, with respect to the energy of its interaction with other portions of the → closed system.

See also: → quasi-; → closed; → subsystem.

In plasma physics, the theory that considers the interactions between waves and particles are of first order only. It ignores all terms of second order in the fluctuating quantities.

See also: → quasi-; → linear; → theory.

An asteroid moving around the Sun having the same mean motion and mean → longitude as a planet, but a different → eccentricity. The asteroid remains near the planet much like a satellite even when its distance is large enough so that it is well outside the planet’s → Hill sphere. The quasi-satellite motion is one class of possible → co-orbital motions of small bodies in 1:1 mean-motion → resonance with a planet. If the quasi-satellite orbit is coplanar with the planet, then the motion is stable in the → secular approximation. When the orbits are inclined enough, an asteroid can be trapped into such a motion for a finite period of time. Earth has several quasi-satellites (mainly 3753 Cruithne, 2002 AA₂₉, 2003 YN₁₀₇), also does Venus (the only one so far discovered, 2002 VE₆₈). The possibility of such orbits was first suggested by J. Jackson (1913, MNRAS 74, 62).

See also: The term quasi-satellite was first used by S. Mikkola & K. Innanen 1997, The Dynamical Behaviour of our Planetary System; Proceedings, p. 345); → quasi-; → satellite.

A region of the solar atmosphere where the gradient of the field line
→ linkage from one boundary to another is large so that the field lines can slip-run rapidly through the → plasma. The QSL results from → magnetic reconnection without → null point.

See also: → quasi-; → separatrix; → layer.

A model of radiative transfer that ignores forward scattering of photons; assuming forward-scattered light as un-scattered.

See also: → quasi-; → single; → scattering; → approximation.

Initial name of → quasars.

See also: → quasi-; → stellar;
→ object.

A quasar with detectable radio emission.

See also: → quasi-; → stellar; → radio; → source.

A form of solid made up of ordered but non-repeating patterns of atoms, a symmetry that is forbidden for periodic crystals. In an ordinary crystal, only 1-, 2-, 3-, 4-, and 6-fold symmetries are possible, since these are the only symmetries that, when combined, can fill space. Prior to the discovery of quasicrystals, it was believed that 5-fold crystal symmetry could never occur. Quasicrystals are remarkable in that some of them display 5-fold or higher-fold forbidden symmetries. They are used as catalysts, in particular at high temperatures, to produce durable kinds of steel, like those used in objects such as razor blades and thin needles made specifically for eye surgery. The Nobel Prize in Chemistry 2011 was awarded to Daniel Schechtman for his discovery of quasicrystals in 1982.

See also: → quasi-; → crystal.

In a dynamical system, a form of motion that is regular but never exactly repeating. Quasiperiodic motion appears when the system contains two or more incommensurate frequencies.

See also: → quasi-; → periodic; → motion.

The last two million years of geologic time, comprising the Pleistocene and Holocene glacial epochs. Estimates of the date of the beginning of the Quaternary vary between 2.5 and 1.6 million years ago.

Etymology (EN): Quaternary, from L. quaternarius “consisting of four,” from quatern(i) “fourt at a time” + -arius “-ary;” → period.

Etymology (PE): Dowrân, → period; cahârom “fourth,” from cahâr “four” + -om “-th.”

1a) To put out or extinguish.

1b) Electronics: To terminate the discharge in a vacuum tube by application of a voltage.

2. To become extinguished.
   

3. To dip a heated object into a liquid to quickly reduce the temperature.

Etymology (EN): M.E. quenchen, from O.E. acwencan “to quench,” form of root of cwincan “to go out, be extinguished.”

Etymology (PE): Oseridan, oserândan, from Yaghnobi oser- “to cool,” Wakhi wəsər-/wəsərt “to fade, wither,” related to Pers. sard “cold, cool” (Kurd. sar, Baluchi sârt, Ossetian sald “cold” ), afsordan, afsârdan “to congeal;” Mid.Pers. sard/sart “cold;” Av. sarəta- “cold;” cf. Skt. śiśira- “cold;” L. calidus “warm;” Lith. šaltas “cold;” Welsh clyd “warm;” PIE *keltos- “cool.”

The frequency at which an oscillation is intermittently quenched, as in a super-regenerative receiver.

See also: → quench; → frequency.

A galaxy in which star formation is turned off or suppressed by some physical processes. → star formation quenching.

See also: → quench; → quenching; → galaxy.

1. The process of extinguishing, removing, or diminishing a physical property.
   

2. In the dealing with star formation in galaxies, the term quenching has been used with two different meanings.
   Either to indicate the termination of the star formation activity, or the process of maintaining a galaxy quiescent over its lifetime, despite the fresh fuel produced by stellar evolution and gas inflows. Given the substantially different timescales involved in the two processes, it remains debated whether one single mechanism is responsible for both the onset and the maintenance of quenching (Man and Belli, 2018, arXiv:1809.00722).

See also: Verbal noun, → quench + → -ing.

A period during which an eruptive astronomical phenomenon is in a state of inactivity.

See also: → quiescent; → -ence.

Being at rest; quiet; still; inactive. → quiescent prominence.

Etymology (EN): From L. quiescens, pr.p. of quiescere, from quies “rest, quiet.”

Etymology (PE): Âramidé
“quiescent, reposed, rested,” from âramidan “to rest, repose,” related to ârâm “quiet” (Mid.Pers. râm “peace,” râmenidan “to give peace, pleasure,” râmišn “peace, pleasure” (Mod.Pers. râmiš), Av. ram- “to stay, rest;” cf. Skt. ram- “to stop, stand still, rest, become appeased;” Gk. erema “quietly, gently;” Goth. rimis “rest;” Lith. rãmas “rest”).

A → solar prominence of relatively cool material that hovers over Sun’s surface for weeks or months with relatively little overall change. Such prominences are suspended above the → chromosphere
by → magnetic fields. A quiescent prominence may suddenly erupt outward and dissipate, often to be replaced, in the same location, by a new one. See also → eruptive prominence; → loop prominence.

See also: → quiescent; → prominence.

The Sun when the 11-year cycle of → solar activity is at a minimum.

Etymology (EN): Quiet, M.E., from from O.Fr. quiete, from L. quies (genitive quietis) “rest, quiet;” → Sun.

Etymology (PE): Xoršid, → Sun; ârâm “quiet, rest, tranquility,” → rest.

In cosmology, a hypothetical new “element,” distinct from any normalmatter (either → baryonic or not) or radiation, intended to explain the observed ever → accelerating expansion of the Universe. Quintessence can have several types and differs from the → cosmological constant in that it can vary in space and time. In modern physics, the four known “elements” are the → baryons (proton, neutron, etc.), the → leptons (neutrinos, electrons, etc.), the → photon, and the hypothetical → non-baryonic matter, which is thought to be 80% of the total matter in the Universe.
The quintessence field is a possibility which can be confirmed or disproved by measurements of the → dark energy value at different → redshifts. In some models, the quintessence is fine-tuned to explain both the → cosmological constant problem and the
→ inflation in the very → early Universe.

Etymology (EN): Literally “fifth essence,” from M.Fr. quinte essence, from M.L. quinta essentia, from L. quinta, fem. of quintus “fifth,” from quinque “five,” cognate with Pers. panj, → five + essentia “being, essence,” from esse “being; → existence” + -entia “-ence.” In Aristotelianism, the fifth element, distinguished from the four earthly elements, was the substance of celestial bodies. Subsequently, quintessence became the purest, most highly concentrated form of a nature or essence.

Etymology (PE): Panjomin gowhar “fifth essence,” from panjomin “fifth,” from panj, → five, cognate with L. quinque, + gowhar “essence, substance; jewel, pearl, gem,” Mid.Pers. gohr “essence, substance; jewel; stock, lineage;” cf. Skt. gôtra- “family, race, lineage, origin.”

Any group of five things or persons. → Stephan’s Quintet.

Etymology (EN): From Fr. quintette, from It. quintetto, diminutive of quinto “fifth,” from L. quintus, related to quinque “five” cognate with Pers. panj→ five.

Etymology (PE): Panjtâyé, from panj, → five, + tâ “fold, plait, ply, part;” Mid.Pers. tâg “piece, part” + -(y)é nuance suffix.

Math.: Of the fifth degree; a quantity of the fifth degree.

Etymology (EN): From L. quint(us) “fifth,” → five,

• → -ic;

Etymology (PE): Panjomik, from panjom “fifth,” from panj “five”

• -om “-th” + -ik, → -ic.

An equation containing unknowns of the fifth power.

See also: → quintic; → equation.

A polynomial of degree five.

See also: → quintic; → polynomial.

A bright → open cluster of stars located within 100 light-years of the center of the Milky Way Galaxy, and one of the three → Galactic center clusters. The Quintuplet cluster was originally noted for its five very bright stars, but it is now known to contain many luminous → massive stars that are not detected at visible wavelengths due to heavy extinction by dust along the line of sight. The cluster is about 4 million years old and had an initial mass over 10⁴ solar masses. The five brighter stars of the cluster are dusty → WC Wolf-Rayet stars. The Quintuplet cluster also contains two → Luminous Blue Variables, the Pistol star and FMM362. The Pistol star has a luminosity 10⁷ times solar making it one of the most luminous stars known. The Quintuplet cluster is more dispersed than the nearby → Arches cluster.

See also: Quintuplet, from the five brightest stars originally observed;
→ cluster.

1. General: A proportional part or share of a fixed total amount or quantity.
   

2. Computers: The amount of a resource (disk, memory, CPU time, etc.)
   that is allocated to a user.

Etymology (EN): From L. quota pars “how big a share?,” from quotus “of what number.”

Etymology (PE): Bahrâl, from bahr “part, portion, share, lot,” → quotient + -âl, → -al.

The number resulting from the division of one number by another. Also the fractional notation that indicates this number.

Etymology (EN): From L. quotiens “how many times,” from quot “how many,” related to quis “who.”

Etymology (PE): Bahr “part, portion, share, lot,” related to
baxš “portion, part, division,” baxšidan “to divide, distribute, grant” (Mid.Pers. baxt “fortune, fate,” baxtan, baxšidan “to distribute, divide;” Av. base bag- “to attribute, allot, distribute,” baxš- “to apportion, divide, give to,”
baxta- “what is allotted (luck, fortune),” baxədra- “part, portion,” baγa- “master, god;” O.Pers. bâji- “tribute, tax;” cf. Skt. bhaj- “to share, divide, distribute, apportion,” bhájati “divides,” bhakta- “allotted; occupied with; a share; food or a meal, time of eating?” pitu-bháj- “enjoying food;” Gk. phagein “to eat (to have a share of food)”; PIE base *bhag- “to share out, apportion”).