An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 50 Search : constant
aberration constant
  پایا‌ی ِ بیراهش   
pâyâ-ye birâheš

Fr.: constante d'aberration   

Same as → constant of aberration.

aberration; → constant.

astronomical constant
  پایا‌ی اخترشناسیک، ~ اخترشناختی   
pâyâ-ye axtaršenâsik, ~ axtaršenâxti (#)

Fr.: constante astronomique   

A precisely measured fundamental quantity in astronomy, such as the → solar parallax, the → constant of aberration, and the → obliquity of the ecliptic.

astronomical; → constant.

Besselian star constant
  پایای ِ اختری ِ بسلی   
pâyâ-ye axtari-ye Besseli

Fr.: constante stellaire besselienne   

Any of the eight quantities denoted by a, b, c, d (for → right ascension) and a', b', c', d' (for → declination) used in conjunction with → Besselian day numbers for the reduction of star's → mean catalog place.

Besselian; → star; → constant.

Boltzmann constant
  پایای ِ بولتسمن   
pâyâ-ye Boltzmann

Fr.: constante de Boltzmann   

Boltzmann's constant.

Boltzmann's constant.

Boltzmann's constant
  پایای ِ بولتسمن   
pâyâ-ye Boltzmann

Fr.: constante de Boltzmann   

The physical constant, noted by k, relating the mean → kinetic energy of → molecules in an → ideal gas to their → absolute temperature. It is given by the ratio of the → gas constant to → Avogadro's number. Its value is about 1.380 x 10-16erg K-1.

Named after the Austrian physicist Ludwig Boltzmann (1844-1906), who made important contributions to the theory of statistical mechanics; → constant.

pâyâ (#)

Fr.: constante   

A quantity that does not change during a particular process.

L. constantem "standing firm, stable," pr.p. of constare, from → com- "together" + stare "to stand;" PIE base *sta- "to stand;" cf. O.Pers./Av. sta- "to stand, stand still; set," Pers. istâdan "to stand," Skt. sthâ- "to stand," Gk. histemi "put, place, weigh," stasis "a standing still,"

pâyâ verbal adj./noun from pâyidan "to stand firm, to be constant, steady, fixed," Mid.Pers. pâyitan, pâtan, pây- "to protect; wait, stand," Sogdian p'y "to protect, watch over," O.Pers./Av. pâ(y)- "to protect, keep" pâtar- "protector, watcher," cf. Skt. pâ- "to protect, keep," pâti "protects," Gk. poimen "shepherd," poma "lid, cover," L. pastor "shepherd," panis "bread;" PIE base *pa- "to protect, guard, pasture, feed."

constant of aberration
  پایا‌ی ِ بیراهش   
pâyâ-ye birâheš

Fr.: constante d'aberration   

The maximum amount of the apparent yearly displacement of a star, resulting from the → aberration of starlight. The value of the constant of aberration, κ, at J2000.0 is 20".49552. κ = (v/c) csc 1", where v is the average speed of the Earth about the Sun and c is the → speed of light in vacuum. The Earth's speed is given by: v = 2πa / [P(1 - e2)1/2], where a is the → semi-major axis of the Earth's orbit, e is the → eccentricity of the Earth's orbit, and P is the → sidereal period of the Earth. Same as → constant of annual aberration. See also → constant of diurnal aberration.

constant; → aberration.

constant of annual aberration
  پایا‌ی ِ بیراهش سالانه   
pâyâ-ye birâheš sâlâné

Fr.: constante d'aberration annuelle   

Same as → constant of aberration.

constant; → annual; → aberration.

constant of diurnal aberration
  پایا‌ی ِ بیراهش روزانه   
pâyâ-ye birâheš ruzâné

Fr.: constante d'aberration diurne   

The quantity 0".3200 ρ cos φ', where ρ is the geocentric distance of the observer measured in units of → equatorial radius the Earth and φ' is the observer's → geocentric latitude. The numerical part is equal to 2πa csc1" / (cP), where a is the equatorial radius of the Earth, P is its → sidereal period of rotation, and c is the → speed of light in vacuum.

constant; → diurnal; → aberration.

constant of gravitation
  پایا‌ی ِ گرانشی   
pâyâ-ye gerâneši (#)

Fr.: constante de la gravitation   

gravitational constant.

constant of the motion
  پایای ِ جنبش   
pâyâ-ye jonbeš

Fr.: constante de mouvement   

1) Classical mechanics: A variable X whose total rate of change dX/dt along the path of a → dynamical system is zero. In other words, a function of an object's position, velocity, or both that does not change even as the object moves. For example, the total energy of a → simple harmonic oscillator is a constant of the motion.
2) Quantum mechanics: An → observable that remains constant in time. As an example, the energy is a constant of the motion of all systems whose → Hamiltonian does not depend explicitly upon time.

constant; → motion.

cosmological constant
  پایای ِ کیهان‌شناسیک، ~ کیهان‌شناختی   
pâyâ-ye keyhânšenâsik, ~ keyhânšenâxti

Fr.: constante cosmologique   

A term introduced by Einstein into his gravitational → field equations in order to allow a solution corresponding to a → static Universe. The cosmological constant is physically interpreted as due to the → vacuum energy of quantized fields. See also → dark energy.

cosmological; → constant.

cosmological constant problem
  پراسه‌ی ِ پایای ِ کیهانشناختی   
parâse-ye pâyâ-ye keyhânšenâxti

Fr.: problème de la constante cosmologique   

The impressive discrepancy of about 120 orders of magnitude between the theoretical value of the → cosmological constant and its observed value. → Quantum field theory interprets the cosmological constant as the density of the → vacuum energy. This density can be derived from the maximum energy at which the theory is valid, i.e. the → Planck energy scale (1018 GeV). The theoretical vacuum → energy density is (1018 GeV)4 = (1027 eV)4 = 10112 erg cm-3. On the other hand, the observed vacuum energy density is estimated to be about (10-3 eV)4 = 10-8 erg cm-3. There is, therefore, a discrepancy of about 120 orders of magnitude.

cosmological; → constant; → problem.

coupling constant
  پایای ِ جفسری   
pâyâ-ye jafsari

Fr.: constante de couplage   

In nuclear physics, a constant that indicates a measure of how strongly two particles interact.

coupling; → constant.

curvature constant
  پارامون ِ خمیدگی   
pârâmun-e xamidegi

Fr.: paramètre de courbure   

A parameter occurring in the → Friedmann equations of → general relativity describing the geometry of → space-time. A spatially → open Universe is defined by k = -1, a → closed Universe by k = + 1 and a → flat Universe by k = 0. See also the → Robertson-Walker metric. See also → curvature of space-time.

curvature; → parameter.

decay constant
  پایای ِ تباهی   
pâyâ-ye tabâhi

Fr.: constante de désintégration   

A constant of proportionality occurring in the formula expressing spontaneous → decay of → radionuclides. The number of atoms decaying is given by N = N0e-kt, where N0 is the number of nuclei in the given volume of the substance at instant t = 0, N is the number of nuclei at t, and k is decay constant. Decay constant is related to → half-life by τ = ln2/k, roughly 0.693/k.

decay; → constant.

Dirac's constant
  پایای ِ دیراک   
pâyâ-ye Dirac

Fr.: constante de Dirac   

The → Planck's constant divided by 2π and denoted ħ, pronounced h-bar. Also called → reduced Planck's constant.

Dirac; → constant.

Einstein's gravitational constant
  پایای ِ گرانشی ِ اینشتین   
pâyâ-ye gerâneši-ye Einstein (#)

Fr.: constante gravitationnelle d'Einstein   

The coupling constant appearing in → Einstein's field equations, expressed by: κ = 8πG/c4, where G is the Newtonian → gravitational constant and c the → speed of light.

einstein; → gravitational; → constant.

Fermi constant
  پایای ِ فرمی   
pâyâ-ye Fermi

Fr.: constante de Fermi   

The → coupling constant associated with the → weak interaction, which gives rise to → beta decay. CF = 1.167 x 10-5 GeV-2.

Fermi; → constant.

fine-structure constant
  پایای ِ ساختار ِ نازک   
pâyâ-ye sâxtâr-e nâzok

Fr.: constante de la structure fine   

A measure of the strength of → interaction between a → charged particle and the → electromagnetic field. It is a → dimensionless number expressed (in → cgs units) by α = e2c, where e is the → electron charge, ħ is the → reduced Planck's constant, and c is the → speed of light. It is approximately equal to 1/137 or 7.3 x 10-3. The smallness of this number is of great importance since it determines the size of → atoms and the → stability of → matter.

fine structure; → constant.

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