An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 3106 Search : on
Eddington factor
  کروند ِ ادینگتون   
karvand-e Eddington

Fr.: facteur d'Eddington   

Same as → Eddington parameter.

Eddington limit; → factor.

Eddington limit
  حد ِ ادینگتون   
hadd-e Eddington (#)

Fr.: limite d'Eddington   

The theoretical upper limit of → luminosity at which the → radiation pressure of a light-emitting body would exceed the body's → gravitational attraction. A star emitting radiation at greater than the Eddington limit would break up. The Eddington luminosity for a non-rotating star is expressed as: LEdd = 4πGMmpcσT-1, where G is the → gravitational constant, M the star mass, mp the → proton mass, c the → speed of light, and σT the → Thomson cross section. It can also be written as LEdd = 4πGMcκ-1, where κ is the → opacity. In terms of solar mass, the Eddington limit can be expressed by: LEdd = 1.26 × 1038 (M/Msun) erg s-1. See also → rotational Eddington limit.

Named after Arthur Stanley Eddington (1882-1944), prominent British astrophysicist; → limit.

Eddington luminosity
  تابندگی ِ ادینگتون   
tâbandegi-ye Eddington

Fr.: luminosité d'Eddington   

Same as → Eddington limit.

Eddington limit; → luminosity.

Eddington parameter
  پارامون ِ ادینگتون   
pârâmun-e Eddington

Fr.: paramètre d'Eddington   

A → dimensionless parameter indicating the degree to which a star is close to the → Eddington limit. It is expressed as Γ = L / LEdd = κ L / (4πGMc), where L and M are the star luminosity and mass respectively, κ is the opacity, c the speed of light, and G the → gravitational constant. At the Eddington limit, Γ = 1, the star would become unbound. Because stellar luminosity generally scales with a high power of the stellar mass (LM3-4), → massive stars with M larger than 10 Msun generally have electron Eddington parameters of order Γ ≅ 0.1-1.

After Arthur Stanley Eddington (1882-1944), prominent British astrophysicist; → parameter.

Eddington-Lemaître Universe
  گیتی ِ ادینگتون-لومتر   
giti-ye Eddington-Lemaître (#)

Fr.: Univers d'Eddington-Lemaître   

A theoretical model in which the → cosmological constant plays a crucial role by allowing an initial phase that is identical to the Einstein static Universe. After an arbitrarily long time, the Universe begins to expand. The difficulty with this model is that the initiation of galaxy formation may actually cause a collapse rather than initiate an → expansion of the Universe.

Eddington limit; Lemaître in honor of Georges-Henri Lemaître (1894-1966), a Belgian Roman Catholic priest, who first proposed the Big Bang theory; → universe.

Eddington-Sweet time scale
  مرپل ِ زمانی ِ ادینگتون-سوییت   
marpel-e zamâni-ye Eddington-Sweet

Fr.: échelle de temps d'Eddington-Sweet   

The time required for the redistribution of → angular momentum due to → meridional circulation. The Eddington-Sweet time for a uniformly → rotating star is expressed as: τES = τKH . GM / (Ω2 R3), where τKH is the → Kelvin-Helmholtz time scale, R, M, and L designate the radius, mass, and luminosity respectively, Ω the → angular velocity, and G the → gravitational constant. The Eddington-Sweet time scale can be approximated by τES≅ τKH / χ, where χ is the ratio of the → centrifugal force to → gravity. For the Sun, χ ≅ 10-5 resulting in an Eddington-Sweet time scale which is too long (1012 years), i.e. unimportant. In contrast, for a rotating → massive star  χ is not so much less than 1. Hence the Eddington-Sweet circulation is very important in massive stars.

Named after the prominent British astrophysicist Arthur S. Eddington (1882-1944), who was the first to suggest these currents (in The Internal Constitution of the Stars, Dover Pub. Inc., New York, 1926) and P. A. Sweet who later quantified them (1950, MNRAS 110, 548); → time scale.

eddy diffusion
  پخش ِ گیژاوی   
paxš-e gižâvi

Fr.: diffusion turbulente   

A macroscopic process that occurs in a → fluid because of the relative motions induced by the non-uniform → turbulent motions of the fluid. Also known as turbulent → diffusion. Eddy diffusion may occur in an atmosphere if it is unstable against turbulence. It dominates the atmosphere below the homopause. See also → molecular diffusion.

eddy; → diffusion.

edge-on galaxy
  کهکشان ِ پهلونما   
kahkašân-e pahlunemâ

Fr.: galaxie vue par la tranche   

A → spiral galaxy oriented edge-on to our view. → face-on galaxy.

edge; on, from O.E. on, variant of an "in, on, into" (cf. Du. aan; Ger. an; Goth. ana "on, upon"), from PIE base *ano "on" (cf. Av. ana "on;" Gk. ana "on, upon;" L. an-); → galaxy.

Kahkašân, → galaxy; pahlunemâ "showing the side," from pahlu, → side, + nemâ, from nemudan "to show, display," → display.

edition
  ۱) ویرایش؛ ۲) ویراست   
1) virâyeš (#); 2) virâst (#)

Fr.: édition   

1) The act or process of editing.
2) A version of anything, printed or not, presented to the public.

Verbal noun of → edit.

education
  فرهیزش   
farhizeš (#)

Fr.: éducation   

The act or process of educating.
The knowledge or abilities gained through being educated.

Verbal noun of → educate.

effective Eddington parameter
  پارامون ِ ادینگتون ِ اسکرمند   
pârâmun-e Eddington-e oskarmand

Fr.: paramètre d'Eddington effectif   

The effective value of the → Eddington parameter in a non-homogeneous system (porous opacity).

effective; → Eddington limit; → parameter.

eigenfunction
  ویژکریا   
viž-karyâ

Fr.: fonction propre   

1) Math.: An → eigenvector for a linear → operator on a → vector space whose vectors are → functions. Also known as proper function.
2) Quantum mechanics: A → wave function corresponding to an → eigenvalue. Eigenfunctions represent the stationary → quantum states of a system.

From Ger. Eigenfunktion, from eigen- "characteristic, particular, own" (from P.Gmc. *aigana- "possessed, owned," Du. eigen, O.E. agen "one's own") + → function.

Viž-karyâ, from viž, contraction of vižé "particular, charcteristic" + karyâ, → function. Vižé, from Mid.Pers. apēcak "pure, sacred," from *apa-vēcak "set apart," from prefix apa- + vēcak, from vēxtan (Mod.Pers. bixtan) "to detach, separate, sift, remove," Av. vaēk- "to select, sort out, sift," pr. vaēca-, Skt. vic-, vinakti "to sift, winnow, separate; to inquire."

Einstein notation
  نمادگان ِ اینشتین   
namâdgân-e Einstein

Fr.: convention Einstein   

A notation convention in → tensor analysis whereby whenever there is an expression with a repeated → index, the summation is done over that index from 1 to 3 (or from 1 to n, where n is the space dimension). For example, the dot product of vectors a and b is usually written as: a.b = Σ (i = 1 to 3) ai.bi. In the Einstein notation this is simply written as a.b = ai.bi. This notation makes operations much easier. Same as Einstein summation convention.

Einstein; → notation.

Einstein's field equations
  هموگش‌های ِ میدان ِ اینشتین   
hamugešhâ-ye meydân-e Einstein

Fr.: équations de champ d'Einstein   

A system of ten non-linear → partial differential equations in the theory of → general relativity which relate the curvature of → space-time with the distribution of matter-energy. They have the form: Gμν = -κ Tμν, where Gμν is the → Einstein tensor (a function of the → metric tensor), κ is a coupling constant called the → Einstein gravitational constant, and Tμν is the → energy-momentum tensor. The field equations mean that the curvature of space-time is due to the distribution of mass-energy in space. A more general form of the field equations proposed by Einstein is: Gμν + Λgμν = - κTμν, where Λ is the → cosmological constant.

Named after Albert Einstein (1879-1955); → field; → equation.

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.

Einstein-Hilbert action
  ژیرش ِ اینشتین-هیلبرت   
žireš-e Einstein-Hilbert

Fr.: action de Einstein-Hilbert   

In → general relativity, the → action that yields → Einstein's field equations. It is expressed by:
SEH = (1/2κ)∫d4x (-g)1/2R + Sm,
where κ ≡ 8πG and Sm is the matter part of the action.

Einstein; → Hilbert space; → action.

ejection
  اشانش   
ešâneš

Fr.: éjection   

Act or instance of ejecting; the state of being ejected.

Verbal noun of → eject.

elastic collision
  همکوبش ِ کشایند   
hamkubš-e kešâyand

Fr.: collision élastique   

A collision between two particles which conserves the total kinetic energy and momentum of the system.

elastic; → collision.

elastic deformation
  وادیسش ِ کشایند   
vâdiseš-e kešâyand

Fr.: déformation élastique   

A deformation of a → solid body in which the change (→ strain) in the relative position of points in the body disappears when the deforming stress is removed. See also → elastic limit.

elastic; → deformation.

electrical conductivity
  هازندگی ِ برقی   
hâznadegi-e barqi

Fr.: conductivité électrique   

A measure of a material's ability to conduct an electrical current. It is the reciprocal of the → resistivity. Conductivity is expressed by σ = ne2l/(2mv), where n is the number of electrons per cm3 volume of the → conductor, e is the → electron charge, l is the → mean free path, m is the → electron mass, and v is the arithmetic mean velocity of thermal motion of electrons at a given temperature.

electrical; → conductivity.


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