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
facilitation
  آسانش   
âsâneš

Fr.: facilitation   

The act or process of facilitating.

facilitate; → -tion.

family of distributions
  خانواده‌ی ِ واباژش‌ها   
xânevâde-ye vâbâžešhâ

Fr.: famille de distributions   

A set of distributions which have the same general mathematical → formula.

family; → distribution.

Fanaroff-Riley classification
  رده‌بندی ِ فاناروف-رایلی   
radebandi-ye Fanaroff-Riley

Fr.: classification Fanaroff-Riley   

A classification scheme for distinguishing a → radio galaxy from an → active galaxy based on their → radio frequency  and → luminosity and their kpc-scale appearance. Analyzing a sample of 57 radio galaxies from the → 3CR catalogue, which were clearly resolved at 1.4 GHz or 5 GHz, Fanaroff & Riley (1974) discovered that the relative positions of regions of high and low → surface brightness in the → lobes of extragalactic → radio sources are correlated with their radio luminosity. They divided the sample into two classes using the ratio RFR of the distance between the regions of highest surface brightness on opposite sides of the central galaxy or quasar, to the total extent of the source up to the lowest brightness contour in the map. → Fanaroff-Riley Class I (FR-I) , → Fanaroff-Riley Class II (FR-II). The boundary between the two classes is not very sharp, and there is some overlap in the luminosities of sources classified as FR-I or FR-II on the basis of their structures. The physical cause of the FR-I/II dichotomy probably lies in the type of flow in the → radio jets.

Bernard L. Fanaroff and Julia M. Riley, 1974, MNRAS 167, 31P; → classification.

Faraday rotation
  چرخش ِ فارادی   
carxeš-e Faraday (#)

Fr.: rotation Faraday   

The rotation of the plane of → polarization experienced by a beam of → linearly polarized radiation when the radiation passes through a material containing a magnetic field with a component in the direction of propagation. This effect occurs in → H II regions in which a magnetic field causes a change in the polarized waves passing through. Same as → Faraday effect.

farad; → rotation.

Faraday's law of induction
  قانون ِ درهازش ِ فارادی   
qânun-e darhazeš-e Faraday

Fr.: loi d'induction de Faraday   

The induced → electromotive force in a circuit is equal in magnitude and opposite in sign to the rate of change of the → magnetic flux through the surface bounded by the circuit. Mathematically, it is expressed as: ∇ x E = -∂B/∂t, which is one of the four → Maxwell's equations.

farad; → law; → induction.

fecundation
  گشنش، گشن‌گیری، بارورسازی   
gošneš, gošngiri (#), bârvarsâzi (#)

Fr.: fécondation   

Biology: The act or process of fecundating.

fecundate; → -tion.

federation
  هیاوش   
hiâyveš

Fr.: fédération   

1) The act of federating or uniting in a league.
2) A political unit formed from smaller units on a → federal basis.

Verbal noun of → federate.

Fermi constant
  پایای ِ فرمی   
pâyâ-ye Fermi

Fr.: constante de Fermi   

The → coupling constant associated with the → weak interaction, which gives rise to → beta decay. CF = 1.167 x 10-5 GeV-2.

Fermi; → constant.

Fermi interaction
  اندرژیرش ِ فرمی   
andaržirš-e Fermi

Fr.: interaction de Fermi   

An old explanation, proposed by Enrico Fermi, of the → weak interaction.

fermi; → interaction.

fermion
  فرمیون   
fermion (#)

Fr.: fermion   

An elementary particle, such as → electron, → proton, or → neutron, having a half integral value of → spin. Fermions obey the → Pauli exclusion principle.

From Fermi → fermi + → -on.

ferric iron
  آهن ِ فریک   
âhan-e ferrik

Fr.: fer ferrique, fer trivalent   

Iron in a plus-3 → oxidation state. Ferric iron needs to share three electrons with an oxygen molecule to make the ion neutral.

ferric; → iron.

ferrous iron
  آهن ِ فرور   
âhan-e fervar

Fr.: fer ferreux, fer bivalent   

Iron in a plus-2 → oxidation state.

ferrous; → iron.

Fibonacci number
  عدد ِ فیبوناچی   
'adad-e Fibonacci

Fr.: nombre de Fobonacci   

One of the numbers in the → Fibonacci sequence.

Fibonacci sequence; → number.

Fibonacci sequence
  پی‌آیه‌ی ِ فیبوناچی   
peyâye-ye Fibonacci

Fr.: suite de Fibonacci   

An infinite sequence of integers, starting with 0 and 1, where each element is the sum of the two previous numbers. For example: 0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, ... As the sequence develops, the ratio of the consecutive terms converges to the → golden ratio, about 1.618.

Leonardo Pisano Fibonacci (1170-1250), medieval Italian mathematician who wrote Liber abaci (1202; Book of the Abacus), the first European work on Indian and Arabian mathematics, which introduced "Arabic" numerals in Europe; → sequence.

fiction
  دیزن   
dizan

Fr.: fiction   

1) Literary works invented by the imagination, such as novels or short stories.
2) An invented story or explanation; lie.
3) The act of inventing a story or explanation.
4) Law: Something assumed to be true for the sake of convenience, though probably false (Dictionary.com).

M.E., from O.Fr. ficcion "dissimulation, ruse; invention, fabrication" and directly from L. fictionem "a fashioning or feigning," noun of action from p.p. stem of fingere "to shape, form, devise, feign," originally "to knead, form out of clay," from PIE *dheigh- "to build, form, knead;" akin to Skt. dehah "body," literally "that which is formed," dih- "to besmear;" Gk. teikhos "wall;" L. fingere "to form, fashion," Gothic deigan "to smear;" O.Irish digen "firm, solid."

Formed on the model of fiction, as above, from diz- "to build, to form;" (related to Pers. dež, dez "fortress"); cf. Mid.Pers. dys-/dēs- "to build;" Sogd. dys "to build;" Av. (+ *pari-) daēz- "to build (around);" Proto-Ir. *daiz- "to build, form;" from PIE *dheigh- "to build, form," as above, + suffix -an.

field equation
  هموگش ِ میدان   
hamugeš-e meydân

Fr.: équation de champ   

In a physical theory, an equation that describe how a fundamental force interacts with matter. Einstein's equations of → general relativity are called field equations since they describe the → gravitational field. Similarly, → Maxwell's equations describe the electromagnetic field.

field; → equation.

field horizontal branch star
  ستاره‌ی ِ شاخه‌ی ِ افقی ِ میدانی   
setâre-ye šâxe-ye ofoqi-ye meydâni

Fr.: étoile de la branche horizontal du champ   

A → horizontal branch star with high velocity.

field; → horizontal; → branch; → star.

field rotation
  چرخش ِ میدان   
carxeš-e meydân

Fr.: rotation de champ   

The effect of the Earth's rotation on the position of the image formed on the → focal plane of a telescope during long exposures. In the case of → equatorial mounting, the image remains fixed, whereas it turns continuously with an → altazimuth mounting. In the latter case the image motion must be compensated by an appropriate mechanism, → field rotator.

field; → rotation.

fine-structure constant
  پایای ِ ساختار ِ نازک   
pâyâ-ye sâxtâr-e nâzok

Fr.: constante de la structure fine   

A measure of the strength of → interaction between a → charged particle and the → electromagnetic field. It is a → dimensionless number expressed (in → cgs units) by α = e2c, where e is the → electron charge, ħ is the → reduced Planck's constant, and c is the → speed of light. It is approximately equal to 1/137 or 7.3 × 10-3. The smallness of this number is of great importance since it determines the size of → atoms and the → stability of → matter. Same as → electromagnetic coupling constant.

fine structure; → constant.

fingering convection
  همبز ِ انگشتوار   
hambaz-e angoštvâr

Fr.:   

A weak yet important kind of mixing that results from → fingering instability in stars within → radiative zones that have an unstable mean → molecular weight  → gradient. Also called → thermohaline convection.

finger; → -ing; → convection.

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