An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 415
sangvâré (#)

Fr.: fossile   

A relic, remnant, or representation of an organism that existed in a past geological age.

From Fr. fossile, from L. fossilis "dug up," from fossus, p.p. of fodere "to dig."

Sangâré literally "resembling stone," from sang, → stone, + -vâré, from -vâr, → -oid.

fossil magnetic field
  میدان ِ مغناتیسی ِ سنگواره، ~ ~ سنگواره‌ای   
meydân-e meqnâtisi-ye sangvâré, ~ ~ sangvâre-yi

Fr.: champ magnétique fossile   

In a physical system, the → magnetic field belonging to an earlier magnetic process or event. A fossil magnetic field may be a vanished one or exist in relic forms. As an example, the solar magnetic field, which was present during the formation of the Sun, has disappeared over the last 4.6 billions years.

fossil;→ magnetic; → field;

Foucault current
  جریان ِ فوکو   
jarayân-e Foucault (#)

Fr.: courant de Foucault   

Same as → eddy current.

Foucault; → current.

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.

Foucault pendulum
  آونگ ِ فوکو   
âvang-e Foucault (#)

Fr.: pendule de Foucault   

A → pendulum consisting of a heavy weight on a very long wire attached to a support, that shows the rotation of Earth. The support must be nearly frictionless in order that the pendulum can continue to swing freely for long periods of time. The pendulum will swing in the same plane as it started. The → Earth's rotation is reflected in the slow turning of the plane of the pendulum's motion, which appears to rotate through 360° in T hours. The rotation time is given by the expression: T = T0/sin φ, where T0 = 23.9344 hours is the → sidereal day and φ the → latitude of the place. At the poles the rotation period is 23h 56m 04s, and at the equator is ∞, i.e. the swing plane does not move. For regions near the equator it is very long; for example at Quito, the capital city of Ecuador, with φ = 00°15'S, it is 5485 days or more than 15 years! This phenomenon shows that the Earth is a → non-inertial frame.

The experiment was performed for the first time by the French physicist Léon Foucault (1819-1868) in 1851, who set up, in the Pantheon in Paris, a simple pendulum consisting of a lead ball weighing 28 kg, suspended by a fine steel wire 67m long. At the latitude of Paris, the pendulum takes 31h 47m 38s to complete a precession cycle; → pendulum.

Foucault's Marseille reflector
  بازتابگر ِ فوکو‌ی ِ مارسی   
bâztâbgar-e Foucault-ye Marseille

Fr.: réflecteur marseillais de Foucault   

The first functioning → reflecting telescope with a silvered glass mirror. It was built by Léon Foucault in 1826 for the Marseille Observatory. The mirror of 80-cm in diameter (f/d = 5) had an excellent quality. The telescope was used for a century as a visual instrument. Edouard Stéphan (1837-1923) used it from 1871 to 1884 to find 800 high-brightness galaxies, among which the → Stephan's Quintet. From 1906 to 1962 the telescope was used by Robert Jonckheere (1888-1927) to discover 3,350 new binary stars. In 1873, following an idea of Hippolyte Fizeau (1819-1896), Stéphan attempted to use it as an → interferometer to measure the diameter of a number of stars. In 1914 Charles Fabry (1867-1945) and Henri Buisson (1873-1944) used the telescope to obtain the first astronomical Fabry-Pérot interferogram, on the → Orion Nebula.

After the French physicist and optician Léon Foucault (1819-1868); Marseille (Observatory), the second largest city of France, located on the south east coast of the Mediterranean Sea, from L. Massalia, from Gk. Massalia; → reflector.

cahâr (#)

Fr.: quatre   

O.E. feower, from P.Gmc. *petwor- (cf. O.S. fiwar, Du. and Ger. vier, O.N. fjorir, Dan. fire, Sw. fyra), cognate with Pers. cahâr, as below, from PIE *qwetwor.

Cahâr, variant câr, from Mid.Pers. cahâr; Av. caθwarô, catur-; cf. Skt. catvārah; Gk. tessares; cognate with L. quattuor; E. four, as above.

four-dimensional operator
  آپارگر ِ چهار-وامونی   
âpârgar-e cahâr-vâmuni

Fr.: opérateur à quatre dimensions   

An operator defined as: ▫ = (∂/∂x, ∂/∂y, ∂/∂z, 1/(jc∂/∂t).

four; → dimensional; → operator.

Fourier analysis
  آنالس ِ فوریه   
ânâlas-e Fourier

Fr.: analyse de Fourier   

The process of decomposing any function of time or space into a sum of sinusoidal functions using the → Fourier series and → Fourier transforms. In other words, any data analysis procedure that describes or measures the fluctuations in a time series by comparing them with sinusoids. Fourier analysis is an essential component of much of modern applied and pure mathematics. It forms an exceptionally powerful analytical tool for solving various problems in many areas of mathematics, physics, engineering, biology, finance, etc. and has opened up new realms of knowledge.

After the French mathematician Baron Jean Baptiste Joseph Fourier (1768-1830), whose work had a tremendous impact on the physical applications of mathematics; → analysis.

Fourier coefficient
  همگر ِ فوریه   
hamgar-e Fourier

Fr.: coefficient de Fourier   

One of the coefficients an or bn of cos (nx) and sin (nx) respectively in the → Fourier series representation of a function. They are expressed by:
an = (1/π) ∫f(x) cos nx dx, for n≥ 0, summed over 0 to 2π
bn = (1/π) ∫f(x) sin nx dx, for n≥ 1, summed over 0 to 2π.

Fourier analysis; → series.

Fourier integral
  درستال ِ فوریه   
dorostâl-e Fourier

Fr.: intégrale de Fourier   

An integral used in the → Fourier transform.

Fourier analysis; → integral.

Fourier series
  سری ِ فوریه   
seri-ye Fourier

Fr.: séries Fourier   

A mathematical tool used for decomposing a → periodic function into an infinite sum of sine and cosine functions. The general form of the Fourier series for a function f(x) with period 2π is:
(1/2) a0 + Σ (an cos (nx) + bn sin (nx), summed from n = 1 to ∞,
where an and bn are the → Fourier coefficients, measuring the strength of contribution from each harmonic. The functions cos (nx) and sin (nx) can be used in this way because they satisfy the → orthogonality conditions. For the problem of convergence of the Fourier series see → Dirichlet conditions. The Fourier series play a very important role in the study of periodic phenomena, because they allow one to decompose a large number of complex problems into simpler ones. The generalization of this method, called the → Fourier transform, makes it possible to also decompose non-periodic functions into harmonic components. See also → complex Fourier series, → Parseval's theorem.

Fourier analysis; → series.

Fourier theorem
  فربین ِ فوریه   
farbin-e Fourier

Fr.: théorème de Fourier   

Any finite periodic motion may be analyzed into components, each of which is a simple harmonic motion of definite and determinable amplitudes and phase.

Fourier analysis; → theorem.

Fourier transform
  ترادیس ِ فوریه   
tarâdis-e Fourier

Fr.: transformée de Fourier   

A powerful mathematical tool which is the generalization of the → Fourier series for the analysis of non-periodic functions. The Fourier transform transforms a function defined on physical space into a function defined on the space of frequencies, whose values quantify the "amount" of each periodic frequency contained in the original function. The inverse Fourier transform then reconstructs the original function from its transformed frequency components. The integral F(α) = ∫ f(u)e-iαudu is called the Fourier transform of F(x) = (1/2π)∫ f(α)eiαxdx, both integrals from -∞ to + ∞.

Fourier analysis; → transform.

fourth contact
  پرماس ِ چهارم   
parmâs-e cahârom

Fr.: quatrième contact   

The end of a solar eclipse marked by the disk of the Moon completely passing away from the disk of the Sun.

From M.E. fourthe, O.E. féowertha, from four, from O.E. feower, from P.Gmc. *petwor- (cf. Du. and Ger. vier, O.N. fjorir, Dan. fire, Sw. fyra), from PIE *qwetwor (cf. Mod.Pers. cahâr, Av. caθwar-, catur-, Skt. catvarah, Gk. tessares, L. quattuor) + -th a suffix used in the formation of ordinal numbers, from M.E. -the, -te, O.E. -tha, -the; cf. O.N. -thi, -di; L. -tus; Gk -tos; → contact.

Parmâs, → contact; cahârom cardinal form from cahâr "four," cognate with E. four, as above.

  لکه‌ی ِ زرد   
lake-ye zard (#)

Fr.: fovéa   

A small depression, approximately 1.5 millimeters in diameter, at the back of the → retina. It forms the area of the most acute vision.

Contraction of fovea centralis, from L. fovea "small pit," of unknown origin.

Lake-ye zard, literally "yellow spot," from laké, → spot, zard, → yellow.

barxâl (#)

Fr.: fractal   

A geometrical or physical structure that repeats itself or nearly repeats itself on many different scales of magnification.

From Fr. fractale, term coined by Benoit Mandelbrot (1975), from frac(tus) "broken, uneven", → fraction, + -ale-al.

Barxâl, from barx, → fraction, + -âl-al.

fractal cosmology
  کیهانشناخت ِ برخالی   
keyhânšenâxt-e barxâli

Fr.: cosmologie fractale   

The postulate that the concentrations of matter in the Universe follow a → fractal structure over a wide range of scales.

fractal; → cosmology.

fractal structure
  ساختار ِ برخالی   
sâxtâr-e barxâli

Fr.: structure fractale   

A → hierarchial structure that can be likened to fractals.

fractal; → structure

barxé (#)

Fr.: fraction   

A rational number of the form a/b where a is called the numerator and b is called the denominator.

From L.L. fractionem (nom. fractio) "a breaking in pieces," from frangere "to break," from PIE base *bhreg- "to break" (cf. Goth. brikan, O.E. brecan "to break;" Lith. brasketi "crash, crack").

Barxé, from barx "lot, portion," variant bahr, from Mid.Pers. bahr "lot, share, portion," Av. baxəδra- "portion."

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