An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 1965 Search : ion

Fr.: durée   

Continuance in time; a period of existence or persistence; length of time during which anything continues.

Noun of action from L. durare "to harden," → during.

Pâyeš, noun of action from pâyidan, → last (v.).

dust coagulation
  ماسش ِ غبار، رچش ِ ~   
mâseš-e qobâr, roceš-e ~

Fr.: coagulation de la poussière   

A process of formation of → dust grains in → interstellar medium and → protoplanetary disks, in which randomly colliding aggregates may stick together.

dust; → coagulation.

dust emission
  گسیل ِ غبار   
gosil-e qobâr

Fr.: émission des poussières   

Thermal emission in infrared from interstellar → dust grains receiving photons. Dust grains absorb ultraviolet and visible light emitted by nearby stars and re-radiate in the infrared wavelengths. Since the infrared light is of lower energy than the ultraviolet/visible light, the difference goes into heating the dust grain. Typical temperatures for interstellar grains are tens of degrees Kelvin.

dust; → emission.

dust obscuration
  تیره‌شد پت غبار   
tirešod pat qobâr

Fr.: obscurcissement par la poussière   

The → absorption of → electromagnetic radiation from an astrophysical object by → dust grains associated with that object.

dust; → obscuration.

Tiregi, → obscuration, pat, → by; qobâr, → dust.

dynamical disruption
  گسیخت ِ توانیک   
gosixt-e tavânik

Fr.: rupture dynamique   

The process whereby a → bound system, such as a → binary system or a → globular cluster, is broken apart.

dynamical; → disruption.

dynamical friction
  مالش ِ توانیک   
mâleš-e tavânik

Fr.: frottement dynamique   

The gravitational interaction between a relatively massive body and a field of much less massive bodies through which the massive body travels. As a result, the moving body loses → momentum and → kinetic energy. An example of dynamical friction is the sinking of massive stars to the center of a → star cluster, a process called → mass segregation. Dynamical friction plays an important role in → stellar dynamics. It was first quantified by Chandrasekhar (1943).

dynamical; → friction.

dynamical relaxation
  واهلش ِ توانیک   
vâheleš-e tavânik

Fr.: relaxation dynamique   

The evolution over time of a gravitationally → bound system consisting of N components because of encounters between the components, as studied in → stellar dynamics. Due to this process, in a → star cluster, → low-mass stars may acquire larger random velocities, and consequently occupy a larger volume than → high-mass stars. As a result, massive stars sink to the cluster centre on a time-scale that is inversely proportional to their mass. See also → mass segregation.

dynamical; → relaxation.

E-mode polarization
  قطبش ِ ترز ِ E   
qotbeš-e tarz-e E

Fr.: polarisation en mode E   

A → polarization component in the → cosmic microwave background radiation that depends only on → gradient, is independent of → curl and does not have → handedness. In contrast to the → B-mode, the E-mode may be due to both the → scalar perturbations and → tensor perturbations.

E, indicating electric-field like; → mode; → polarization.

e-term of aberration
  بیراهش ِ ترم ِ e   
birâheš-e tarm-e e

Fr.: aberration elliptique   

The same as → elliptic aberration.

e, → elliptic; → term; → aberration.

Earth's rotation
  چرخش ِ زمین   
carxeš-e zamin (#)

Fr.: rotation de la Terre   

The natural motion of the Earth around its own axis, which takes place once in a → sidereal day. The Earth rotates toward the → east, in the same direction as it revolves around the Sun. If viewed from the north celestial pole, the Earth turns → counterclockwise. The opposite is true when the Earth is viewed from the south celestial pole. The Earth's rotation is responsible for the diurnal cycles of day and night, and also causes the apparent movement of the Sun across the sky. The Earth's rotation velocity at the → equator is 1,673 km h-1 or about 465 m s-1. More generally, at the → latitude  φ it is given by: vφ = veq cos φ, where veq is the rotation velocity at the equator. The Earth's rotation is gradually slowing down under the action of the → tides, which are generated by the → gravitational attraction of the → Moon. As the result of this → tidal friction, the day is becoming longer at a rate of about 2 milliseconds, or 0.002 seconds, per century (or one second every 50,000 years). Moreover, the loss of the Earth's → rotational angular momentum increases the Moon's → orbital angular momentum, because the angular momentum of the → Earth-Moon system is conserved. In consequence, the Moon slowly recedes from the Earth by about 4 cm per year, which leads to increasing its orbital period and the length of a month as well.

Earth; → rotation.

eastern elongation
  درازش ِ خاوری   
derâzeš-e xâvari

Fr.: élongation est   

The position of a planet when it can be seen in the western sky just after sunset.

eastern; → elongation.

eclipse obscuration
  تیره‌شد ِ خورگرفت   
tirešod-e xorgereft

Fr.: obscuration de l'éclipse   

The fraction of the Sun's area occulted by the Moon. It should not be confused with → eclipse magnitude, which is the fraction of the Sun's diameter occulted by the Moon. Eclipse obscuration may be expressed as either a percentage or a decimal fraction (e.g., 50% or 0.50) (F. Espenak, NASA).

eclipse; obscuration, verbal noun from → obscure.

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.

  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.

farhizeš (#)

Fr.: éducation   

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

Verbal noun of → educate.


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) In the Einstein notation this is simply written as a.b = 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.

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