An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 442
freezing point
  نقطه‌ی ِ یخ‌بست   
noqte-ye yaxbast

Fr.: point de congélation   

1) The temperature at which a liquid of specified composition changes into a solid under a specified pressure.
2) The temperature at which the liquid and solid phases of a substance of specified composition coexist in equilibrium.

freezing; → point.

French Republican Calendar
  گاهشمار ِ جمهوری ِ فرانسه   
gâhšomâr-e jomhuri-ye Farâncé

Fr.: Calendrier républicain, Calendrier révolutionnaire français   

A calendar composed by Fabre d'Eglantine and others during the French Revolution which divided the year into 12 months of 30 days each, with five odd days called → Sansculottides. The year started at → autumnal equinox and the months were: Vendémiaire (Vintage), Brumaire (Fog), Frimaire (Frost), Nivôse (Snow), Pluviôse (Rain), Ventôse (Wind), Germinal (Buds), Floréal (Flowers), Prairial (Meadows), Messidor (Harvest), Termidor (Heat), Fructidor (Fruits). The week consisted of 10 days, and was called a Décade; each 10th day of Décade (called Décadi) was a day of rest. The calendar was used by the French government for about 12 years, from late 1793 to 1805, when it was suppressed by Napoleon.

M.E. Frensh, French, O.E. Frencisc "of the Franks," from Frank; republican, from republic, from Fr. république, from L. respublica, from res publica "public interest, the state," from res "affair, matter, thing" + publica, feminine of publicus "public;" → calendar.

  بسامد، فرگی   
basâmad (#), feregi (#)

Fr.: fréquence   

The number of complete oscillations per unit time of a vibrating system. The reciprocal of the → period, T.

From L. frequentia "assembly, multitude, crowd."

Basâmad, from bas "many, much" (Mid.Pers. vas "many, much;" O.Pers. vasiy "at will, greatly, utterly;" Av. varəmi "I wish," vasô, vasə "at one's pleasure or will," from vas- "to will, desire, wish") + âmad past stem of âmadan "to occur, to come, to become" (Mid.Pers. âmatan; O.Pers. gam- "to come; to go," Av. gam- "to come; to go," jamaiti "goes;" Proto-Iranian *āgmatani; Skt. gamati "goes;" Gk. bainein "to go, walk, step;" L. venire "to come;" Tocharian A käm- "to come;" O.H.G. queman "to come;" E. come; PIE root *gwem- "to go, come").
Feregi, from feré "much, more; increase; priority," farâ(vân) "abundant," Mid.Pers. frêh "more, much;" O.Pers. fra- "before, forth;" Av. frā, fərrā "forth, forward;" PIE base *pro-; cf. L. pro "on behalf of, in place of, before, for;" Gk. pro- "before, in front of."

frequency band
  باند ِ بسامد   
bând-e basâmad

Fr.: bande de fréquence   

A range of frequencies that is continuous between two specified limits, selected from a more extended range of frequencies.

frequency; → band.

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.

frequency spectrum
  بیناب ِ بسامد   
binâb-e basâmad

Fr.: spectre de fréquence   

A graphical display of the intensity of radiation or energy versus frequency.

frequency; → spectrum.

frequency switching
  دگربانی ِ بسامد   
degarbâni-ye basâmad

Fr.: permutation de fréquence   

A mode of observation in radio astronomy in which the telescope remains at a fixed position and data is accumulated while the center of the receiver passband is switched between signal and offset frequencies. Data accumulated at the offset frequency is subtracted from the signal frequency data before storage as a frequency switched scan. → beam switching.

frequency; → switching.

frequency to wavelength conversion
  هاگرد ِ بسامد به موج-طول   
hâgard-e basâmad bé mowj-tul

Fr.: conversion fréquence / longueur d'onde   

Deriving the → wavelength of an undulatory phenomenon from its → frequency, and vice versa.
1) For → electromagnetic waves: λ = c / f, where λ is the wavelength, c is the → speed of light in → meters per second and f the frequency in → hertz. It can be written as: λ (m) = 2.998 × 108 / f (Hz).
2) For → sound waves: λ = C / f, where C is the → sound speed. For air at temperature 0°C, λ (m) = 332 / f (Hz).

frequency; → wavelength; → conversion.

Fresnel diffraction
  پراش ِ فرنل   
parâš-e Fresnel (#)

Fr.: diffraction de Fresnel   

The diffraction effects obtained when either the source of light or observing screen, or both, are at a finite distance from diffracting aperture or obstacle. → Fraunhofer diffraction.

Named after Jean Augustin Fresnel (1788-1827), French physicist, a key figure in establishing the wave theory of light. His earlier work on interference was carried out in ignorance of that of Thomas Young (1773-1829), English physician and physicist, but later they corresponded and were allies; → diffraction.

Fresnel equation
  هموگش ِ فرنل   
hamugeš-e Fresnel

Fr.: équation de Fresnel   

For an electromagnetic wave incident upon the interface between two media with different indices of refraction, one of a set of equations that give the → reflection coefficient and → transmission coefficient at the optical interface. These coefficients depend on the polarization degree of the incident wave.

Fresnel diffraction; → equation.

Fresnel integrals
  درستال‌های ِ فرنل   
dorostâlhâ-ye Fresnel

Fr.: intégrales de Fresnel   

Two integrals that involve quadratic equations in the sine and cosine functions and are defined as: C(x) = ∫ cos (πt2/2) dt and C(y) = ∫ sin (πt2/2) dt, integrated from 0 to x. They are quite frequently used in optics studying → Fresnel diffraction and similar topics. The Fresnel integrals are also used in railway and freeway constructions. These integrals may be evaluated to arbitrary precision using → power series. Alternatively the amplitudes may be found graphically by use of → Cornu's spiral.

Fresnel diffraction; → integral.

Fresnel lens
  عدسی ِ فرنل   
adasi-ye ferenel (#)

Fr.: lentille de Fresnel   

An optical lens composed of a series of rings of glass so curved that they all have the same focus. It is flat on one side and ridged on the other making it possible that nearly every ray of light from the source be re-directed out on a horizontal path. This design enables the construction of lenses of large aperture and short focal length avoiding thus the large weights and volumes of material which would be required in conventional lenses. The first Fresnel lens, designed for use in a lighthouse on the river Gironde, was installed in France in 1823, and by the 1850s many examples were in use everywhere. Fresnel lenses are most often used in light gathering applications, such as condenser systems or emitter/detector setups. They can also be used as magnifiers and projection lenses. Nowadays, Fresnel lenses made of optical plastics are widely used for various applications.

Fresnel diffraction; → lens.

Fresnel mirror
  آینه‌ی ِ فرنل   
âyene-ye Fresnel (#)

Fr.: miroir de Fresnel   

A pair of plane mirrors which are slightly inclined to one another. It is used for producing two coherent images in interference experiments.

Fresnel diffraction; → mirror.

Fresnel rhomb
  لوزی‌وار ِ فرنل   
lowzivâr-ye Fresnel

Fr.: parallélépipède de Fresnel   

A piece of special glass in the form of an oblique → parallelepiped so cut that a ray of light entering one of its faces at right angles shall emerge at right angles at the opposite face, after undergoing two internal reflections. It is a type of → quarter-wave retarder used to produce a → circularly polarized light from a → plane polarized light, or the reverse.

Fresnel diffraction; → rhombus.

Fresnel's biprism
  دومنشور ِ فرنل   
domanšur-e Fresnel (#)

Fr.: biprisme de Fresnel   

An optical element consisting of two small angle → prisms, joined together at their bases, used to produce two → coherent sources. The thin double prism refracts the light from a source into two overlapping beams, which produce → interference fringes. With this experiment Fresnel was able to produce interference without relying upon → diffraction to bring the interfering beams together.

Fresnel diffraction; → bi-; → prism.

Fresnel's mirrors
  آینه‌های ِ فرنل   
âyenehâ-ye Fresnel (#)

Fr.: miroirs de Fresnel   

Two plane mirrors, fitted side by side at a small angle, used to create two mutually → coherent sources in a famous → interference experiment first suggested by A. Fresnel. A point source reflected at the mirrors appears as a pair of → virtual light sources, positioned close together, which interfere with each other due to their → coherence. This arrangement removes the problem that two separate light sources do not produce observable interference on account of their incoherence. Same as Fresnel's double mirror. See also → Fresnel's biprism, → Lloyd's mirror.

Fresnel diffraction; → mirror.

mâleš (#)

Fr.: frottement   

The resisting force offered by one body to the relative motion of another body in contact with the first.

From L. frictionem "a rubbing, rubbing down," from fricare "to rub."

Mâleš, verbal noun of mâlidan "to rub," from, variants parmâs "contact, touching," marz "frontier, border, boundary," Mid.Pers. mâlitan, muštan "to rub, sweep;" Av. marəz- "to rub, wipe," marəza- "border, district;" PIE base *merg- "boundary, border;" cf. L. margo "edge" (Fr. marge "margin"); P.Gmc. *marko; Ger. Mark; E. mark, margin.

Fried parameter
  پارامون ِ فرید   
pârâmun-e Fried

Fr.: paramètre de Fried   

One of the parameters that characterize atmospheric → seeing. It is the diameter of the largest aperture that can be used before → turbulence starts to degrade the image quality. As the turbulence gets stronger, the Fried parameter, denoted r0, becomes smaller. The Fried parameter is wavelength dependent: r0 ∝ λ6/5. On best astronomical mountain tops it ranges between 20 and 30 cm for λ = 5000 A.

Named after David L. Fried, who defined the parameter 10 1966; → parameter.

Friedmann equation
  هموگش ِ فریدمن   
hamugeš-e Friedmann

Fr.: équation de Friedmann   

An equation that expresses energy conservation in an → expanding Universe. It is formally derived from → Einstein's field equations of → general relativity by requiring the Universe to be everywhere → homogeneous and → isotropic. It is expressed by H2(t) = (8πG)/(3c2)ε(t) - (kc2)/R2(t), where H(t) is the → Hubble parameter, G is the → gravitational constant, c is the → speed of light, ε(t) is the → energy density, k is the → curvature of space-time, and R(t) is the → cosmic scale factor. See also → Big Bang, → accelerating Universe. See also → Friedmann-Lemaitre Universe.

Named after the Russian mathematician and physical scientist Aleksandr Aleksandrovich Friedmann (1888-1925), who was the first to formulate an → expanding Universe based on Einstein's theory of → general relativity ; → equation.

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