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: 285 Search : if
drift velocity
  تندای ِ دلک   
tond-ye delek

Fr.: vitesse de dérive   

The average velocity of a charged particle in a plasma in response to an applied electric field.

drift; → velocity.

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.

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.

electron diffraction
  پراش ِ الکترونی   
parâš-e elekroni (#)

Fr.: diffraction des électrons   

A diffraction phenomenon resulting from the passage of electrons through matter, analogous to the diffraction of visible light. This phenomenon is the main evidence for the existence of waves associated with elementary particles; → de Broglie wavelength.

electron; → diffraction.

element diffusion
  پخش ِ بن‌پار   
paxš-e bonpâr

Fr.: diffusion des éléments   

An important physical process occurring in stars, which is the relative separation of the various → chemical elements. It is caused by → gravitational settling and → thermal diffusion, on the one hand, and → radiative levitation on the other. This process, which was described by Michaud (1970) to account for the abundance anomalies observed in → chemically peculiar  → A star, is now recognized as occuring in all types of stars. Its influence on the observed → chemical abundances is extremely variable, however, due to competing macroscopic motions like → convective  → mixing or rotation-induced → turbulence. In the Sun, no observable abundance anomalies are expected from element diffusion, as the time scale of the process is longer than the solar lifetime. However the small induced → depletion of → helium and → heavy elements by about 20% is detectable through → helioseismology. Such detections are more difficult in stars, as only global → oscillation modes can be detected, in contrast to the Sun, where local oscillations of the surface can be analyzed (Théado et al., 2005, A&A 437, 553).

element; → diffusion.

ether drift
  دلک ِ اتر   
delek-e eter

Fr.: dérive de l'éther   

1) The hypothetical motion of the supposed → ether relative to the Earth. The → Michelson-Morley experiment found no ether drift. An analogy is given by a boat drifting in a fast-flowing river due to the river's current. With the same power, the speed would be slower when sailing across the stream. Moreover, in order to reach directly opposite the starting point, the boat would have to be headed somewhat upstream. See also the → ether drag.
2) The motion of the Earth relative to the → rest frame defined by the → cosmic microwave background radiation.

ether; → drift.

exact differential
  دگرسانه‌ی ِ رزین   
degarsâne-ye razin

Fr.: différentielle exacte   

If N(x,y) is a → function of two → independent variables, then dN = (∂N/∂x)dx + (∂N/∂y)dy is the exact differential.

exact; → differential.

exact differential equation
  هموگش ِ دگرسانه‌ای ِ رزین   
hamugeš-e degarsâneyi-ye razin

Fr.: équation différentielle exacte   

A → differential equation composed of → continuous  → differentiable functions for which certain conditions are fulfilled. The equation M(x,y)dx + N(x,y)dy = 0 is called exact if M(x,y) and N(x,y) are continuous differentiable functions for which the following relationship is fulfilled: ∂M/∂y = ∂N/∂x, and ∂M/∂y and ∂N/∂x are continuous in some region.

exact; → differential; → equation.

existential quantifier
  چنداگر ِ هستیال   
candâgar-e hastiyâl

Fr.: quantificateur existentiel   

A symbol of → predicate logic which expresses that the statements within its scope are → true for at least one instance of something. The symbol ∃ is used as the existential quantifier. Existential quantifiers are normally used in logic in → conjunction with → predicate symbols, which say something about a → variable or → constant, in this case the variable being quantified (→ quantify, → quantification).

existential; → quantifier.

exolife
  برونزیست   
borunzist

Fr.: vie extraterrestre   

extraterrestrial life.

exo-; → life.

extraterrestrial life
  زیست ِ استرزمینی   
zist-e ostarzamini

Fr.: vie extraterrestre   

Life that may exist and originate outside the planet Earth.

extraterrestrial; → life.

falsifiability
  زیفیدنیگی، زیفش‌پذیری   
zifidanigi, zifešpaziri

Fr.: falsifiabilité   

Philosophy of science: The concept according to which a proposition or theory cannot be scientific if it does not admit consideration of the possibility of its being false. According to Karl Popper (1902-1994), falsifiability is the crucial feature of scientific hypotheses. Any theory not falsifiable is said to be unscientific.

falsifiable; → -ity.

falsifiable
  زیفیدنی، زیفش‌پذیر   
zifidani, zifešpazir

Fr.: falsifiable   

The quality of something that can be falsified. → falsifiability.

falsify; → -able.

falsify
  زیفیدن   
zifidan

Fr.: falsifier   

1) To show or prove that a theory is incorrect or false.
2) To alter something in order to deceive.

Verb from → false.

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.

first-order differential equation
  هموگش ِ دگرسانه‌ای ِ رایه‌ی ِ نخست   
hamugeš-e degarsâne-yi-ye râye-ye naxost

Fr.: équation différentielle du premier ordre   

A → differential equation containing only the first → derivative. For example, dy/dx = 3x and 2y(dy/dx) + 3x = 5.

first; → order; → differential; → equation.

flat manifold
  بسلای ِ تخت   
baslâ-ye taxt

Fr.: variété plate   

A manifold with a → Riemannian metric that has → zero → curvature.

flat; → manifold.

Foucault knife-edge test
  آزمون ِ کارد ِ فوکو   
âzmun-e kârd-e Foucault

Fr.: contrôle par foucaultage   

A method used to test the → image quality of → mirrors and → lenses. The test is performed by moving a knife edge laterally into the → image of a small → point source. The → eye, or a → camera, is placed immediately behind the knife edge, and the → exit pupil of the system is observed.

Named after the French physicist Léon Foucault (1819-1868), who invented the method; → knife; → edge; → test.

frequency drift
  دلک ِ بسامد   
delek-e basâmad

Fr.: dérive de fréquence   

An undesired progressive change in an oscillator's frequency with time.

frequency; → drift.

frequency shift
  کیب ِ بسامد   
kib-e basâmad

Fr.: décalage de fréquence   

The change in the frequency of a wave motion due to the → Doppler effect.

frequency; → shift.

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