An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 678
double pulsar
  پولسار ِ دوتایی، تپار ِ ~   
pulsâr-e dotâyi, tapâr-e ~ (#)

Fr.: pulsar double   

A → binary pulsar consisting of two pulsars. The only known example is PSR J0737-3039 (A and B), discovered in 2003 (Burgay et al. Nature 426, 531). The rotation periods of the pulsars are 22.7 and 2.8 milliseconds respectively. Each of them has a mass about 1.3 times that of the Sun and revolves around their → center of gravity with a period of 2.4 hours. According to the theory of → general relativity, such a binary should lose energy through the emission of → gravitational waves. As deduced from the change in orbital period, the separation of the pulsars is reducing by about 7 mm per day, in exact agreement with theory. It is expected that the pulsars will eventually merge in about 85 million years.

double; → pulsar.

double refraction
  شکست ِ دوتایی   
šekast-e dotâyi

Fr.: double réfraction   

Formation of two refracted rays of light from a single incident ray; property of certain crystals, notably calcite.

double; → refraction.

double root
  ریشه‌ی ِ دوتایی   
riše-ye dotâyi

Fr.: racine double   

A → root x0 of function f(x), if f(x0) = 0, df/dx | x0 = 0, and d2f/dx2 | x0≠ 0. See also → simple root.

double; → root.

double shell burning
  سوزش ِ پوسته‌ی ِ دوتایی   
suzeš-e puste-ye dotâyi

Fr.: combustion double coquille   

A situation in the evolution of an → asymptotic giant branch star whereby both hydrogen and helium shells provide energy alternatively. As the burning → helium shell approaches the hydrogen-helium discontinuity, its luminosity decreases because it runs out of the fuel. As a consequence, the layers above contract in response, thus heating the extinguished → hydrogen shell until it is re-ignited. However, the shells do not burn at the same rate: the He burning shell becomes thermally unstable and undergoes periodic → thermal pulses.

double; → shell; → burning.

double slit
  شکاف ِ دوتایی   
šekâf-e dotâyi (#)

Fr.: fente double   

A pair of adjacent holes or slits made on a dark and plane surface, used in optical experiments, such as interference and diffraction.

double; → slit.

double star
  ستاره‌ی ِ دوتایی   
setâre-ye dotâyi (#)

Fr.: étoile double   

An apparently single star which better observational resolution shows it to be a pair of closely lying stars. They may or may not be physically related.

double; → star.

double vision
  دوبینی   
dobini (#)

Fr.: vision double   

Same as → diplopia.

double; → vision.

double white dwarf
  سفیدکوتوله‌ی ِ دوتایی   
sefid kutule-ye dotâyi

Fr.: naine blanche double   

A → double-lined binary with two → white dwarf components. Short-period double white dwarfs can lose → orbital angular momentum by emitting → gravitational radiation and if the total mass of the binary exceeds the → Chandrasekhar limit, their eventual → merger might produce a → Type Ia supernova.

double; → white; → dwarf.

double-degenerate binary system
  راژمان ِ درین ِ دوبار واگن   
râžmân-e dorin-e dobâr vâgen

Fr.: système binaire doublement dégénéré   

A system of evolved → binary stars in which both → components have ejected their envelopes and evolve toward → white dwarf stage. So far a half dozen double-degenerate → binary systems are known, for example Henize 2-248 (M. Santander-Garcia et al., 2015, 518, 5).

double; → degenerate; → binary; → system.

double-diffusive convection
  همبز ِ دوپخشی   
hambaz-e do paxši

Fr.:   

An instability involving two layers of fluid with opposite gradients of properties. Same as → fingering instability. See also → salt finger. Double-diffusive instabilities commonly occur in any astrophysical fluid that is stable according to the → Ledoux criterion, as long as the entropy and chemical stratifications have opposing contributions to the dynamical stability of the system. They drive weak forms of convection, and can cause substantial heat and compositional → mixing. Two cases can be distinguished. In fingering convection, entropy is stably stratified (∇ - ∇ad < 0), but chemical composition is unstably stratified (∇μ < 0); it is often referred to as → thermohaline convection by analogy with the oceanographic context in which the instability was first discovered. In oscillatory double-diffusive convection, entropy is unstably stratified (∇ - ∇ad > 0), but chemical composition is stably stratified (∇μ > 0); it is related to semiconvection, but can occur even when the → opacity is independent of composition (P. Garaud, 2014, arXiv:1401.0928).

double;→ diffusive; → system.

double-lined binary
  دورین ِ دوخطه   
dorin-e doxatté

Fr.: binaire à double raies   

A → spectroscopic binary in which the spectra of both stars are seen and the lines are alternatively double and single. → single-lined binary.

double; → line; → binary

double-lined eclipsing binary
  دورین ِ گرفتی ِ دوخطه   
dorin-e gerefti-ye doxatté

Fr.: binaire à éclipse à double raies   

A → double-lined spectroscopic binary whose → light curve is typical of an → eclipsing binary.

double; → line; → eclipsing; → binary.

double-lobed radio source
  خن ِ رادیویی با لپ ِ دوتایی   
xan-e râdioyi bâ lap-e dotâyi

Fr.: radio source à double lobe   

A → galaxy that emits radio energy from two regions located on opposite sides of the galaxy.

double; → lobe; → radio; → source.

double-slit experiment
  آزمایش ِ شکاف ِ دوتایی   
âzmâyeš-e šekâf-e dotâyi (#)

Fr.: expérience de double fente   

An experiment of → diffraction and → interference of two light beams using a → double slit; → Young's experiment.

double; → slit; → experiment.

doublet
  دوتایه   
dotâyé

Fr.: doublet   

A pair of forbidden spectral lines of the same atom arising from a common upper excitation level, for example [O III] λ 5007 and [O III] λ 4959, [N II] λ 6584 and [N II] λ 6548, and [S II] λ 6717, [S II] λ 6731.
A pair of associated lines arising from transitions having a common lower energy level in a spectrum characteristic of the alkali metals.

From O.Fr. doublet, from → double + -et diminutive suffix.

Dotâyé, from dotâdouble + -(y)é nuance suffix.

doubly
  دوبار-، دو-، دوتایی   
dobâr-, dv-, dotâyi

Fr.: double, à ~   

1) To a double measure or degree.
2) In a double manner. → doubly convex, → doubly ionized, → doubly refracting crystal.

double; → -ly (; → twice).

doubly convex
  دو-کوژ   
do-kuž

Fr.: double-convexe   

Describing a → lens which is → convex on both sides.

doubly; → convex.

doubly ionized
  دوبار یونیده   
dobâr yonidé (#)

Fr.: deux fois ionisé   

An atom that has lost two of its external electrons, for example O++ ([O III]).

doubly; → ionized.

doubly refracting crystal
  بلور ِ شکست ِ دوتایی   
bolur-e šakst-e dotâyi

Fr.: cristal à double réfraction   

A → transparent → crystalline substance (such as calcite, quartz, and tourmaline) that is → anisotropic relative to the → speed of light. A ray incident normally on such crystals is broken up into two rays in traversing the crystal, → ordinary ray and → extraordinary ray.

doubly; → refracting; → crystal.

down
  پایین   
pâyin (#)

Fr.: en bas, vers le bas   

Toward or in a lower physical position.
See also: → download, → downgrade, → upload, → downsizing, → meltdown, → overload, → spin-down, → top-down structure formation.

M.E. doun, from O.E. dune "downward," short for adune, ofdune, from a-, of "off, from" + dune "hill."

Pâyin "bottom, below; at the foot of," from pâ(y) "foot; step;" Mid.Pers. pâd, pây; Av. pad- "foot;" cf. Skt. pat; Gk. pos, genitive podos; L. pes, genitive pedis; E. foot; Ger. Fuss; Fr. pied; PIE *pod-/*ped-.

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