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

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Number of Results: 12948 Search : far
einstein
  اینشتین   
einstein (#)

Fr.: einstein   

A unit of radiation energy sometimes used in the investigation of photochemical processes. The unit is defined as NA, where NA is → Avogadro's number and is the energy of a → quantum of the radiation. One einstein (or Einstein unit) is the energy per → mole of photons carried by a beam of monochromatic light.

Named for Albert Einstein (1879-1955).

Einstein coefficient
  همگر ِ اینشتین   
hamgar-e Einstein

Fr.: coefficient d'Einstein   

A measure of the probability that a particular atomic transition leading to the formation of an atomic spectral line occurs. The coefficient of spontaneous emission is denoted by Aij, and the coefficient of stimulated emission by Bij, i representing the lower level and j is the upper level.

Named after Albert Einstein (1879-1955) who introduced the coefficients in 1916; → coefficient.

Einstein cross
  چلیپای ِ اینشتین   
calipâ-ye Einstein

Fr.: croix d'Einstein   

An image of a distant quasar (redshift 1.7) formed by a foreground spiral galaxy (redshift 0.039) through gravitational lensing. The image of the quasar is split into four point sources forming a cross at the center of the galaxy.

Einstein; → cross.

Einstein equivalence principle
  پروز ِ هموگ-ارزی ِ اینشتین   
parvaz-e hamug-arzi-ye Einstein

Fr.: principe d'équivalence d'Einstein   

The → equivalence principle as stated by Einstein, on which is based the theory of → general relativity. It comprises the three following items:
1) The → weak equivalence principle is valid.
2) The outcome of any local non-gravitational experiment is independent of the velocity of the freely-falling → reference frame in which it is performed. Also known as → local Lorentz invariance.
3) The outcome of any local non-gravitational experiment is independent of where and when in the Universe it is performed. Also called → local position invariance.

Einstein; → equivalence; → principle.

Einstein model
  مدل ِ اینشتین   
model-e Einstein

Fr.: modèle d'Einstein   

A model for the → specific heat of solids in which the specific heat is due to the vibrations of the atoms of the solids. The vibration energy is → quantized and the atoms have a single frequency, ν. Put forward in 1907 by Einstein, this model was the first application of → quantum theory to the solid state physics. The expression for the specific heat is given by: CV = 3Rx2ex/(ex -1)2, where R is the → gas constant, x = TE/T, TE = hν/k, h is → Planck's constant, and k is → Boltzmann's constant. TE is called the → Einstein temperature. This model could explain the temperature behavior of specific heat but not very satisfactorily at low temperatures. It has therefore been superseded by the → Debye model. See also → Dulong-Petit law.

Albert Einstein in 1907; → model.

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 radius
  شعاع ِ اینشتین   
šo'â'-e Einstein

Fr.: rayon d'Einstein   

In gravitational lens phenomenon, the critical distance from the → lensing object for which the light ray from the source is deflected to the observer, provided that the source, the lens, and the observer are exactly aligned. Consider a massive object (the lens) situated exactly on the line of sight from Earth to a background source. The light rays from the source passing the lens at different distances are bent toward the lens. Since the bending angle for a light ray increases with decreasing distance from the lens, there is a critical distance such that the ray will be deflected just enough to hit the Earth. This distance is called the Einstein radius. By rotational symmetry about the Earth-source axis, an observer on Earth with perfect resolution would see the source lensed into an annulus, called Einstein ring, centered on its position. The size of an Einstein ring is given by the Einstein radius: θE = (4GM/c2)0.5 (dLS/(dL.dS)0.5, where G is the → gravitational constant, M is the mass of the lens, c is the → speed of light, dL is the angular diameter distance to the lens, dS is the angular diameter distance to the source, and dLS is the angular diameter distance between the lens and the source. The equation can be simplified to: θE = (0''.9) (M/1011Msun)0.5 (D/Gpc)-0.5. Hence, for a dense cluster with mass M ~ 10 × 1015 Msun at a distance of 1 Gigaparsec (1 Gpc) this radius is about 100 arcsec. For a gravitational → microlensing event (with masses of order 1 Msun) at galactic distances (say D ~ 3 kpc), the typical Einstein radius would be of order milli-arcseconds.

Einstein; → radius.

Einstein ring
  حلقه‌ی ِ اینشتین   
halqe-ye Einstein

Fr.: anneau d'Einstein   

The apparent shape of a background source unsergoing the effect of → gravitational lensing as seen from Earth, provided that the source, the intervening lens, and the observer are in perfect alignement through → Einstein radius.

Einstein; → ring.

Einstein solid
  مدل ِ اینشتین   
model-e Einstein

Fr.: modèle d'Einstein   

Same as → Einstein model.

Einstein; → solid.

Einstein static Universe
  گیتی ِ ایستای ِ اینشتین   
giti-ye istâ-ye Einstein

Fr.: Univers stationnaire d'Einstein   

A cosmological model in which a static (neither expanding nor collapsing) Universe is maintained by introducing a cosmological repulsion force (in the form of the cosmological constant) to counterbalance the gravitational force.

Einstein; → static; arr; universe.

Einstein temperature
  دمای ِ اینشتین   
damâ-ye Einstein (#)

Fr.: température d'Einstein   

A characteristic parameter occurring in the → Einstein model of → specific heats.

Einstein; → temperature.

Einstein tensor
  تانسور ِ اینشتین   
tânsor-e Einstein (#)

Fr.: tenseur d'Einstein   

A mathematical entity describing the → curvature of → space-time in → Einstein's field equations, according to the theory of → general relativity. It is expressed by Gμν = Rμν - (1/2) gμνR, where Rμν is the Ricci tensor, gμν is the → metric tensor, and R the scalar curvature. This tensor is both symmetric and divergence free.

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

Einstein time-scale
  مرپل ِ زمانی ِ اینشتین   
marpel-e zamâni-ye Einstein

Fr.: échelle de temps d'Einstein   

The time during which a → microlensing event occurs. It is given by the equation tE = RE/v, where RE is the → Einstein radius, v is the magnitude of the relative transverse velocity between source and lens projected onto the lens plane. The characteristic time-scale of → microlensing events is about 25 days.

Einstein; → time-scale.

Einstein's elevator
  بالابر ِ اینشتین   
bâlâbar-e Einstein

Fr.: ascenseur d'Einstein   

A → thought experiment, involving an elevator, first conceived by Einstein to show the → principle of equivalence. According to this experiment, it is impossible for an observer situated inside a closed elevator to decide if the elevator is being pulled upward by a constant force or is subject to a gravitational field acting downward on a stationary elevator. Einstein used this experiment and the principle of equivalence to deduce the bending of light by the force of gravity.

einstein; elevator, from L. elevator, agent noun from p.p. stem of elevare "to lift up, raise," from → ex- "out" + levare "lighten, raise," from levis "light" in weight, → lever.

Bâlâbar, → lift.

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's theory of specific heat
  نگره‌ی ِ گرمای ِ آبیزه‌ی ِ اینشتین   
negare-ye garmâ-ye âbize-ye Einstein

Fr.: théorie de la chaleur spécifique d'Einstein   

Same as → Einstein model.

Einstein; → theory; → specific heat.

Einstein-de Sitter effect
  اسکر ِ اینشتین-دو سیتر   
oskar-e Einstein-de Sitter

Fr.: effet Einstein-de Sitter   

Same as → geodetic precession.

Einstein-de Sitter Universe; → effect.

Einstein-de Sitter Universe
  گیتی ِ اینشتین-دو سیتر   
giti-ye Einstein-de Sitter

Fr.: Univers Einstein-de Sitter   

The → Friedmann-Lemaitre model of → expanding Universe that only contains matter and in which space is → EuclideanM > 0, ΩR = 0, ΩΛ = 0, k = 0). The Universe will expand at a decreasing rate for ever.

Einstein; de Sitter, after the Dutch mathematician and physicist Willem de Sitter (1872-1934) who worked out the model in 1917; → Universe.

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.

<< < -es -iv -ti 21- A r abe abs abs acc acc acc act act ada adi adu aff age alc Alf ali all alp alt ama amp ana ang ang ann ano ant ant ape apo app aps arc Arg ari art ass ast ast ast atm ato att aur aut axi B r bac Bal Bar Bar Bay bec Ber Bet Bie bij bin bio bis bla bla blu blu bol Bor bou Bra bre bro Bug C-s cal Cam can car Car Cas cat cav cel cen cer Cha cha cha che cho cir cir cir cla clo clo clu coa coe coh col col col com com com com com com com com com con con con con con con con con con con con coo cor cor cor cos cos cos Cou cou Cra Cre cri cro cub cur cyc cyl dar dat daw de- Deb dec dec dee def deg del Den dep der det deu dew dic dif dif dil dip dir dis dis dis dis dis div dog Dop dou dra dua dus dwa dyn e-m ear ecl eco eff ein Ein elb ele ele ele ele Els emi emp ene enr env epi equ equ Eri est Euc eva evo exc exc exh exo exp exp ext ext f-n Fah fam fau fee Fer fib fil fin fir fix fle flu foc for for for fra fre fre fri fun fuz gal gal gal Gan gau GCN gen geo geo geo geo Gl glo gra gra gra gra gra gre gro GW1 hab hal han HAR haz hea hel hel Hen Her heu Hig Hil hol hop hor hou Hub Hum Hyd hyd hyd hyp hys ide ign ima imp imp inc inc ind ine inf inf inf inh INP ins ins int int int int Int int int int inv ion iri irr iso iso iso Jea Jos Jun K2 Kep key kin Kol lag lam Lan lar las lav lea leg len lev lig lim lin lin lin lis lob loc log lor low lum lun lun Lym Mac mag mag mag mag mag mai Mal mar mas mas mat max mea mea mee Men mer met met met mic mid Mil min Mir mix mod mod mol mon Mor mou mul muo mys nan nat nav nec Nep neu New New NGC nob nom non non nor not nuc nuc num Nyq obj obs obs oce oen OH omn opa ope opt opt opt orb ord Ori ort osc out ove oxy pal pan par Par par par pas pea Pen per per per per per pet pha pho pho pho phy pie Pit Pla pla pla pla ple Poi pol pol pol pol pop pos pos pow pre pre pre Pre pri pri pri pro pro pro pro pro pro Pro pub pul pyr qua qua qua qua Qui rad rad rad rad rad rad ram ran rat rea rec rec rec red ref ref reg reg rel rel rem rep res res res ret rev rho Rie rim riv rol Ros rot rul S a Sah san Sat sca Sch Sch scr sec sec sec sei sel sem sep set sha she sho sid sig sil sim sin sit sky slu sno sof sol sol sol sol sou sou spa spa spe spe spe sph spi spl spr sta sta sta sta sta ste ste sti sto str str sub sub sub sug sun sup sup sup sup sur syl syn sys tal Tay tel ten ter tex the the the thi tho thu tid tim tod top tot tra tra tra tra tri tri tro tru tur twi Typ UFO ult unc uni uni uni upg ura uti val var vec vel ver ver vig vir vis voc von wak Was wav wax wea wei whi Wie win WN6 wom X-r yel you zer zod > >>