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: 3079 Search : on
fractional
  برخه‌ای   
barxe-yi

Fr.: fractionnaire, fractionné, partiel   

1) Math.: Pertaining to fractions; constituting a fraction.
2) Chemistry: Of or relating to any process by which parts of a mixture are separated by exploiting differences in their physical properties, such as their boiling points, solubility, or other characteristics.

fraction; → -al.

fractional sky coverage
  پوشش ِ برخه‌ای ِ آسمان   
pušeš-e barxe-yi-ye âsmân

Fr.: couverture partielle du ciel   

The portion of the 4π → steradians of the sky that a radiotelescope can observe from a given location on Earth over a 24-hour time interval.

fractional; → sky; → coverage.

fractionate
  برخاندن   
barxândan

Fr.: fractionner   

1) To break something up into smaller parts.
2) To separate a mixture into ingredients or portions having different properties, as by distillation or otherwise.

From → fraction + -ate a suffix forming verbs or nouns, from L. -atus, -ata, -atum.

Barxândan, from barx, barxé, → fraction, + -ândan suffix of transitive verbs.

fractionation
  برخانش   
barxâneš

Fr.: fractionnement   

1) Any of various methods of separating the components of a mixture into fractions of different properties.
2) → isotope fractionation

Verbal noun from → fractionate.

fragmentation
  لتپارش   
latpâreš

Fr.: fragmentation   

Generally, the process of breaking up into smaller parts. In particular, the splitting of a large molecular cloud into smaller, denser clumps. → cloud fragmentation.

From → fragmenta + -ation, a combination of -ate and -ion, used to form nouns from stems in -ate.

Latpâreš, verbal noun from latpâridan, → fragment.

fragmentation process
  فراروند ِ لتپارش   
farâravand-e latpâreš

Fr.: processus de fragmentation   

The succession of physical events that results in the breaking of a → molecular cloud into several → fragments.

fragmentation; → process.

free electron
  الکترون ِ آزاد   
elektron-e âzâd (#)

Fr.: électron libre   

An electron that is not attached to an → atom, → molecule, or → ion and is free to move under the influence of a present electric or magnetic field.

free; → electron.

free expansion phase
  فاز ِ سپانش ِ آزاد   
fâz-e sopâneš-e âzâd

Fr.: phase d'expansion libre   

The first phase of → supernova remnant (SNR) evolution in which the surrounding → interstellar medium (ISM) has no influence on the expansion of the → shock wave, and the pressure of the interstellar gas is negligible. The shock wave created by the → supernova explosion moves outward into the interstellar gas at highly → supersonic speed. Assuming that most of the → supernova energy  ESN is transformed into → kinetic energy of the ejected gas, the ejection velocity ve can be estimated from ESN by using ESN = (1/2) Meve2, which leads to ve = (2ESN / Me)(1/2), where Me is the ejected mass. The schematic structure of the SNR at this phase can be described as follows: behind the strong → shock front which moves outward into the ISM, compressed interstellar gas accumulates forming a → shell of interstellar gas. This shell of swept-up material in front of shock does not represent a significant increase in the mass of the system. After some time the accumulated mass equals the ejected mass of stellar material, and it will start to affect the expansion of the SNR. By definition, this is the end of the free expansion phase, and the corresponding radius of the SNR, called → sweep-up radius, RSW, is defined by Me = (4π/3) RSW3ρ0, that is RSW = (3Me / 4πρ0)(1/3), where ρ0 is the initial density of the ISM. This radius is reached at the sweep-up time tSW = RSW/ve. The free expansion phase lasts some 100-200 years until the mass of the material swept up by the shock wave exceeds the mass of the ejected material. Then the following → snowplow phase starts.

free; → expansion; → phase.

free oscillation
  نَوِش ِ آزاد   
naveš-e âzâd

Fr.: oscillation libre   

Oscillation of any system in stable equilibrium under the influence of internal forces only, or of a constant force originating outside the system, or of both.

free; → oscillation.

free-bound emission
  گسیل ِ آزاد-بندیده   
gosil-e âzâd-bandidé

Fr.: émission libre-liée   

The radiation emitted when a → free electron is captured by an → ion. See also: → free-free emission; → bound-free transition.

free; → bound; → emission.

free-free emission
  گسیل ِ آزاد-آزاد   
gosil-e âzâd-âzâd (#)

Fr.: emission libre-libre   

Electromagnetic radiation produced in a → plasma by → free electrons scattering off → ions without being captured. The electrons are free before the interaction and remain free afterward.

free; → emission.

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.

friction
  مالش   
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.

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.

front
  رو، پیشان   
ru, pišân

Fr.: face, front   

1) The part or side of anything that faces forward. → ionization front.
2) Meteo.: A narrow zone of transition between air masses of contrasting density, that is, air masses of different temperature or different water vapor concentration or both.
3) The side of the → planispheric astrolabe that displays the → limb of the → mater, the → tympanum, the → rete, and, in some models, the → rule. By setting the front, i.e., by rotating the rete around the mater, one can depict the appearance of the heavens as determined by observation in order to obtain a time value from the instrument. Alternatively, by configuring the rete for a given day, one can perform several astronomical computations such as the rising, culmination, and setting of the Sun, Moon, planets, and stars (online museo galileo, VirtualMuseum).

From O.Fr. front "forehead, brow," from L. frontem "forehead," perhaps lit. "that which projects," from PIE *bhront-, from base *bhren- "to project, stand out."

Pišân, from pišâni "front, forehead," from piš "before; in front," from Mid.Pers. pêš "before, earlier;" O.Pers. paišiya "before; in the presence of" + -ân suffix of place and time.
Ru "face," → surface.

front-end
  پیش-ته   
piš-tah

Fr.:   

A device containing a radio-frequency amplifier and associated cryogenic systems, routers, and converters (mixers), whose input is the voltage from a receptor and whose output is an intermediate-frequency signal. → back-end.

front + end, from O.E. ende, from P.Gmc. *andja, originally "the opposite side," from PIE *antjo "end, boundary," from base *anta-/*anti- "opposite, in front of, before."

Piš-tah, from piš, → front, + tah "end;" Mid.Pers. tah "bottom." The origin of this term is not clear. It may be related to Gk. tenagos "bottom, swamp," Latvian tigas "depth;" PIE *tenegos "water bottom."

frontier
  مرز   
marz (#)

Fr.: frontière   

A border between two countries.
A line of division between different or opposed things.
The farthermost limits of knowledge or achievement in a particular subject.

From O.Fr. fronter, from front "forehead, brow," → front.

Marz, from Mid.Pers. marz "boundary;" Av. marəza- "border, district," marəz- "to rub, wipe;" Mod.Pers. parmâs "contact, touching" (→ contact), mâl-, mâlidan "to rub;" PIE base *merg- "boundary, border;" cf. L. margo "edge" (Fr. marge "margin"); P.Gmc. *marko; Ger. Mark; E. mark, margin.

Frontier Fields
  میدانهای ِ مرزی   
Meydânhâ-ye Marzi

Fr.: Champs frontialers   

An observing project using the → Hubble Space Telescope (HST) and the → Spitzer Space Telescope to obtain deep images for cosmological studies. The Frontier Fields combines the power of HST and Spitzer with the natural gravitational telescopes of massive high-magnification clusters of galaxies to produce the deepest observations of clusters and their lensed galaxies ever obtained. Six clusters (Abell 2744, MACSJ0416.1-2403, MACSJ0717.5+3745, MACSJ1149.5+2223, Abell S1063, and Abell 370) were selected based on their lensing strength, sky darkness, Galactic extinction, parallel field suitability, accessibility to ground-based facilities, HST, Spitzer and JWST observability, and preexisting ancillary data. (Lotz et al., 2016, arxiv/1605.06567 and references therein).

frontier; → field.

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