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: 304 Search : act
compound fraction
  برخه‌ی ِ چندساخت   
barxe-ye candsâxt

Fr.: fraction composée   

Same as → complex fraction.

compound; → fraction.

compression factor
  کروند ِ تنجش   
karvand-e tanješ

Fr.: facteur de compression   

In thermodynamics, the quantity Z = pVm/RT, in which P is the gas pressure, Vm the molar volume, R the gas constant, and T the temperature. The compression factor is a measure of the deviation of a real gas from an ideal gas. For an ideal gas the compression factor is equal to 1.

compression; → facteur.

conformal compactification
  همپکانش ِ همدیس   
hampakâneš-e hamdi

Fr.: compactification conforme   

A mapping of an infinite → space-time onto a finite one that may make the far away parts of the former accessible to study. The technique invented by Penrose defines an equivalence class of → metrics, gab being equivalent to ĝab = Ω2gab, where Ω is a positive scalar function of the space-time that modifies the distance scale making the asymptotics of the physical metric accessible to study.

conformal; → compactification.

contact
  ۱) پرماس؛ ۲) پرماسیدن   
1) parmâs (#); 2) parmâsidan (#)

Fr.: 1) contact; 2) contacter, toucher   

1a) The act or state of touching or being in immediate proximity, as in a → contact binary.
1b) One of the instances when the apparent position of the edges of the Sun and the Moon cross one another during an eclipse. They are designated as the → first contact, → second contact, → third contact, and → fourth contact. See also → contact binary, → last contact.
2a) (v. intr.) To be in or come into contact.
2b) (v.tr.) To bring or put in contact.

From L. contactus "a touching," p.p. of contingere "to touch," from → com- "together" + tangere "to touch."

Parmâs "contact, touching," stem of parmâsidan "to touch, feel," from *pari-mars-, from Indo-Iranian *pari- "around" (O.Pers. pariy "around, about," Av. pairi "around, over," Skt. pari) + *mars- "to touch; to wipe, rub," Mid.Pers. marz "contact, touching," marzitan "to touch," Mod.Pers. mâlidan "to rub," Av. marəz- "to rub, wipe," marəza- "border, district," Skt. mrś- "to touch," mrśáti; L. mulceo "to caress," margo "edge" (Fr. marge "margin"); P.Gmc. *marko; Ger. Mark; E. mark, margin.

contact binary
  دورین ِ پرماسی   
dorin-e parmâsi

Fr.: binaire de contact   

A binary system in which the two components are so close that they exchange gases in a complex manner. Their overlapping gravitational fields form a "peanut" shaped equipotential surface.

contact; → binary.

continued fraction
  برخه‌ی ِ پیداشته   
barxe-ye peydâšté

Fr.: fraction continue   

In mathematics, a fraction whose numerator is an integer and whose denominator is an integer plus a fraction whose numerator is an integer and whose denominator is an integer plus a fraction and so on.

continued; → fraction.

contract
  ترنگیدن   
terengidan

Fr.: se contracter, contracter   

1) To become smaller, shorter, tighter, as a metal when cooled.
2) To reduce to smaller size by or as if by squeezing or forcing together, e.g. contract a muscle.
contraction, → gravitational contraction, → Kelvin-Helmholtz contraction, → length contraction, → Lorentz contraction, → vena contracta.

From M.E., from O.F., from L. contractus, p.p. of contrahere "to draw together," from → com- "together" + trahere "to draw."

Terengidan, variant taranjidan [Dehxodâ] "to contract, become rough and hard, to be squeezed, compressed," Borujerdi terengessa "cramped, tightly dressed," Malâyeri terengidan "to be tightly dressed, cramped in a garment," related to tarang "horse girth, a strap for fastening a load," Proto-Iranian *trng- "to pull tight, squeeze, compress;" PIE base *strenk- "to pull tight, twist; tight, narrow" (cf. L. stringere "to bind or draw tight;" Gk. strangein "to twist;" Lith. stregti "to congeal;" O.E. streccian "to stretch," streng "string;" Ger. stramm, Du. stram "stiff").

contraction
  ترنگش   
terengeš

Fr.: contraction   

An act or instance of contracting; the quality or state of being contracted.
gravitational contraction, → Kelvin-Helmholtz contraction, → length contraction, → Lorentz contraction.

Verbal noun of → contract.

conversion factor
  کروند ِ هاگرد   
karvand-e hâgard

Fr.: facteur de conversion   

1) A numerical factor that, by multiplication or division, translates one unit or value into another.
2) In → molecular cloud studies, a factor used to convert the → carbon monoxide (CO) line intensity to → molecular hydrogen (H2) → column density; usually denoted XCO = I(CO) / N(H2). This useful factor relates the observed CO intensity to the cloud mass. A general method to derive XCO is to compare the → virial mass and the 12CO (J = 1-0) luminosity of a cloud. The basic assumptions are that the CO and H2 clouds are co-extensive, and molecular clouds obey the → virial theorem. However, if the molecular cloud is subject to ultraviolet radiation, selective → photodissociation may take place, which will change the situation. Moreover, molecular clouds may not be in → virial equilibrium. To be in virial equilibrium molecular clouds must have enough mass, greater than about 105 solar masses. The way → metallicity affects XCO is a matter of debate, and there is no clear correlation between XCO and metallicity. Although lower metallicity brings about higher ultraviolet fields than in the solar vicinity, other factors appear to be as important as metallicity for the determination of XCO. In the case of the → Magellanic Clouds, XCO(SMC) = 14 ± 3 × 1020 cm-2 (K km s-1)-1, which is larger than XCO (LMC) = 7 ± 2 × 1020 cm-2 (K km s-1)-1. An independent method to derive XCO is to make use of the gamma ray emission from a cloud. The flow of → cosmic ray protons interacts with interstellar low-energy hydrogen nuclei in clouds creating neutral → pions. These pions quickly decay into two gamma rays. It is therefore possible to estimate the number of hydrogen nuclei and hence the cloud mass from the gamma ray counts. Such a gamma-ray based conversion factor is estimated to be 2.0 × 1020 cm-2 (K km s-1)-1 for Galactic clouds, in good agreement with the result obtained from the virial method. However, the gamma ray flux is not well known in general, so this method is uncertain as well. See, e.g., Fukui & Kawamura, 2010 (ARAA 48, 547).

conversion; → factor.

corotating interaction region (CIR)
  ناحیه‌ی ِ اندرژیرش ِ هم‌چرخنده   
nâhiye-ye andaržireš-e hamcarxandé

Fr.: région d'interaction en corotation   

A spiral-shaped density enhancement formed around a star when fast stellar winds collide with slower material. This large-scale wind structure can extend from the stellar surface to possibly several tens of stellar radii. The CIRs can be produced by intensity irregularities at the stellar surface, such as dark and bright spots, magnetic loops and fields, or non-radial pulsations. The surface intensity variations alter the radiative wind acceleration locally, which creates streams of faster and slower wind material. CIRs are responsible for the → discrete absorption components seen in some ultraviolet → resonance lines of → hot stars (S. R. Cranmer & S. P. Owocki, 1996, ApJ 462, 469).

corotate; → interaction; → region.

cosmic scale factor
  کروند ِ مرپل ِ کیهانی   
karvand-e marpal-e keyhâni

Fr.: facteur d'échelle cosmologique   

A quantity, denoted a(t), which describes how the distances between any two galaxies change with time. The physical distance d(t) between two points in the Universe can be expressed as d(t) = R(t).x, where R(t) is the → scale factor and x the → comoving distance between the points. The cosmic scale factor is related to the → redshift, z, by: 1 + z = R(t0)/R(t1), where t0 is the present time and t1 is the time at emission of the radiation. The quantity (1 + z) gives the factor by which the → Universe has expanded in size between t1 and t0. It is also related to the → Hubble parameter by H(t) = R.(t)/R(t), where R.(t) is the time → derivative of the scale factor. In an → expanding Universe the scale factor increases with time. See also the → Friedmann equation.

cosmic; → scale; → factor.

Coulomb interaction
  اندرژیرش ِ کولن   
andaržireš-e Coulomb

Fr.: interaction de Coulomb   

The reciprocal force between two or more → charged particles according to → Coulomb's law.

coulomb; → interaction.

deactivate
  فروژیراندن   
foružirândan

Fr.: désactiver   

To cause to be → inactive; remove the → effectiveness of (Dictionary.com).

de-; → activate.

decimal fraction
  برخه‌ی ِ دهدهی   
barxe-ye dahdahi

Fr.: fraction décimale   

A fraction expressed by using → decimal representation, as opposed to a vulgar fraction. For example, 2/5 is a vulgar fraction; 0.40 is a decimal fraction.

decimal; → fraction.

deuterium enrichment factor
  کروند ِ پرباری ِ دوتریوم   
karvand-e pordâri-ye doteriom

Fr.: facteur d'enrichissement en deutérium   

The ratio between the D/H value in → water and in → molecular hydrogen, as expressed by:
f = [(1/2)HDO/H2O]/[(1/2)HD/H2] = (D/H)H2O/(D/H)H2.
When f> 1, there is → deuterium enrichment.

deuterium; → enrichment; → factor.

deuterium fractionation
  برخانش ِ دوتریوم   
barxâneš-e doteriom

Fr.: fractionnement de deutérium   

The difference between the deuterium (D)/hydrogen (H) → abundance → ratio in an object with respect to that representing a standard or mean value for that type of objects. Same as → isotope fractionation of deuterium. In the gas phase chemistry many of the D fractionation reactions produce an excess of D atoms relative to → hydrogen atoms. Deuterium fractionation in → interstellar cloud cores, → protostars, and → Solar System bodies is frequently used to infer important aspects of their physical and chemical histories. For example, the → deuterium enhancement in the Earth's sea water, with respect to the cosmic abundance, has been interpreted as being due to → enrichment by → comet-like → planetesimals colliding with the young Earth.

deuterium; → fractionation.

differential refraction
  شکست ِ دگرسانه‌ای   
šekast-e dagarsâneyi

Fr.: refraction différentielle   

A problem encountered in astronomical spectroscopy, which consists of a loss of light from some wavelengths due to → atmospheric dispersion. In simple terms, differential refraction means that at nonzero → zenith distances an object cannot be simultaneously placed at the same position within a → slit at all wavelengths. This problem becomes more important for increasing → airmass, larger → spectral range, and smaller → slitwidths. To remedy this drawback, the slit should always be oriented along a direction perpendicular to the horizon, since differential refraction occurs in that direction.

differential; → refraction.

diffract
  پراشیدن   
parâšidan (#)

Fr.: diffracter   

Verbal form of → diffraction.

diffraction.

diffraction
  پراش   
parâš (#)

Fr.: diffraction   

A wave property of light which allows it to curl around obstacles whose size is about that of the wavelength of the light. As a → wavefront of light passes by an opaque edge or through an opening, secondary weaker wavefronts are generated, apparently originating at that edge. These secondary wavefronts will interfere with the primary wavefront as well as with each other to form a → diffraction pattern.
Related terms: → diffusion; → dispersion; → distribution; → scatter; → scattering.

From Fr. diffraction, from Mod.L. diffractionem, from L. diffrac-, stem of diffringere "break in pieces," from → dis- "apart" + frangere "to break."

Parâš "dispersion, scattering," variant of pâš, pâšidan, → dispersion.

diffraction grating
  توری ِ پراش   
turi-ye parâš (#)

Fr.: réseau de diffraction   

An optical device containing thousands of very fine parallel grooves which produce interference patterns in a way which separates out all the components of the light into a spectrum.

diffraction; → grating.

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