An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < amb dif dif gas > >>

Number of Results: 78 Search : iff
differential refraction
  شکست ِ دگرسانه‌ای   
šekast-e dagarsâneyi

Fr.: refraction différentielle   

A problem encountered in astronomical spectroscopy, which consists of a loss of light from some wavelengths due to → atmospheric dispersion. In simple terms, differential refraction means that at nonzero → zenith distances an object cannot be simultaneously placed at the same position within a → slit at all wavelengths. This problem becomes more important for increasing → airmass, larger → spectral range, and smaller → slitwidths. To remedy this drawback, the slit should always be oriented along a direction perpendicular to the horizon, since differential refraction occurs in that direction.

differential; → refraction.

differential rotation
  چرخش ِ دگرسانه‌ای   
carxeš-e degarsâneyi

Fr.: rotation différentielle   

1) Of a single body (such as a star or a gaseous planet), the axial rotation of equatorial latitudes faster than polar latitudes.
2) Of a galaxy, the orbiting of stars nearer the center faster than those at the edge.

differential; → rotation.

differentially rotating system
  راژمان ِ دگرسانه چرخان   
râžmân-e degarsâné carxân

Fr.: système en rotation différentielle   

A system characterized by → differential rotation. In such a system the → angular velocity decreases as the distance from the rotation center increases.

differential; → rotating; → system.


Fr.: différencier   

General: To perceive or show the difference in or between.
Math.: To obtain the differential or the derivative of.

M.L. differentiatus "distinguished," p.p. of differentiare.

Degarsânidan, verbal form of → difference.

differentiated interior
  درونه‌ی ِ دگرسانیده   
darune-ye degarsânidé

Fr.: intérieur différencié   

A description of a planet's interior which is composed of a rocky, dense inner core and a less dense outer crust.

Differentiated, p.p. of → differentiate; → interior.

differentiated meteorite
  شخانه‌ی ِ دگرسانیده، شهاب‌سنگ ِ ~   
šaxâne-ye degarsânidé, šahâbsang-e ~

Fr.: météorite différenciée   

A meteorite that has distinctly separated stone, metal, and glass. It is derived from a differentiated parent body and hence not primitive. The parent body accreted surrounding material until it was large enough to start melting in the middle. The denser metals sank to the center and the stones and glasses floated to the top. A differentiated meteorite made completely of metal comes from the center of a parent meteoroid which was broken apart. → undifferenciated meteorite.

Differentiated, p.p. of → differentiate; → meteorite.


Fr.: (Math.) dériver; (Astro.) différenciation   

1) Math.: The operation of finding the → derivative of a function.
2) Astro.: Process by which an originally homogeneous planetary or asteroidal body is separated into regions of different composition, such as core, mantle, and crust.

Verbal noun of → differentiate.

došvâr (#)

Fr.: difficile   

Not easy to do or to understand; hard to deal with.

Back-formation from difficulty; L. difficilis. "hard," from → dis- "not, away from" + facilis "easy to do," from facere "to do," → fact.

Došvâr, from Mid.Pers. dušwâr "difficult, disagreeable," variant dušxwâr antonym of xwâr "easy; light; low; mean, abject;" with prefix duš- "ill, evil, bad," → dys-.

parâšidan (#)

Fr.: diffracter   

Verbal form of → diffraction.


parâš (#)

Fr.: diffraction   

A wave property of light which allows it to curl around obstacles whose size is about that of the wavelength of the light. As a → wavefront of light passes by an opaque edge or through an opening, secondary weaker wavefronts are generated, apparently originating at that edge. These secondary wavefronts will interfere with the primary wavefront as well as with each other to form a → diffraction pattern.
Related terms: → diffusion; → dispersion; → distribution; → scatter; → scattering.

From Fr. diffraction, from Mod.L. diffractionem, from L. diffrac-, stem of diffringere "break in pieces," from → dis- "apart" + frangere "to break."

Parâš "dispersion, scattering," variant of pâš, pâšidan, → dispersion.

diffraction grating
  توری ِ پراش   
turi-ye parâš (#)

Fr.: réseau de diffraction   

An optical device containing thousands of very fine parallel grooves which produce interference patterns in a way which separates out all the components of the light into a spectrum.

diffraction; → grating.

diffraction pattern
  الگوی ِ پراش   
olgu-ye parâš (#)

Fr.: tache de diffraction   

A series of concentric rings of dark and light color produced by interference.

diffraction; → pattern.

Olgu, loanword from Turkish; parâšdiffraction.

diffraction spike
  سیخک ِ پراش   
sixak-e parâš

Fr.: aigrette de diffraction   

One of several light rays emanating from a bright light source in images taken with → reflecting telescopes. They are artifacts caused by light diffracting around the support or → spider vanes of the → secondary mirror.

diffraction; → spike.

  کران‌مند به پراش   
karânmand bé parâš

Fr.: limité par la diffraction   

The quality of an → optical system that is capable of producing images with angular resolution as small as the theoretical limit of the → Airy disk.

diffraction; limited, adj. of → limit.

Karânmand "bounded, limited," from karânboundary + -mand possession suffix; parâš diffraction.

  ۱) پخشیدن؛ ۲) پخشیده   
1) paxšidan (#); 2) paxšidé (#)

Fr.: 1) diffuser; 2) diffus   

1a) To pour out, to spread in all directions.
1b) To spread by → diffusion.
2) Spread out, diffused, scattered, as → diffuse reflection.
See also: → diffuse atomic cloud, → diffuse galactic light, → diffuse interstellar band, → diffuse interstellar band carrier, → diffuse interstellar cloud, → diffuse interstellar medium, → diffuse molecular cloud, → diffuse nebula, → diffuse reflection, → diffuse transmission, → diffusion.

L. diffusus "spread, poured forth," from dif- "apart, in every direction," variant of → dis- + fuse, from fusus "melted, poured, cast," p.p. of fundere "to melt, cast, pour out," from PIE *gheud-, from root *gheu- "to pour."

Paxšidan "to diffuse, scatter, disperse," infinitive of paxš "scattered, dispersed; withered, trodden," (Manichean) Mid.Pers. pxš "to wither, fade; to grow ripe," Proto-Iranian *paxš- "to cook," cf. Av. pac- "to cook," pacika- "cooked," Mod.Pers. paz-, poxtan "to cook, bake," Skt. pac- "to cook," pakva- "ripe," Gk. peptein "to cook, ripen," L. coquere "to cook," from which V.L. cocus "cook," from which O.E. coc "cook;" PIE *pekw- "to cook, ripen;" paxšidé, p.p. of paxšidan.

diffuse atomic cloud
  ابر ِ اتمی ِ پخشیده   
abr-e atomi-ye paxšidé

Fr.: nuage atomique diffus   

A type of cloud in the → interstellar medium with low molecular content that is fully exposed to the → interstellar radiation field, and therefore nearly all its → molecules are quickly destroyed by → photodissociation. Hydrogen is mainly in → neutral atomic form (→ neutral hydrogen), and atoms with → ionization potentials less than that of hydrogen (most notably → carbon) are almost fully → ionized, providing abundant electrons. The paucity of molecules implies that very little chemistry occurs in such clouds. Many → sightlines with low → extinction seem to pass exclusively through → diffuse atomic gas. Such sightlines typically have a → column density, NH, less than about 5 × 1020 cm-2, and are sufficiently → optically thin to be observable by means of → visible and → ultraviolet → absorption line measurements. Diffuse atomic clouds typically have a fairly low → density (~ 10-100 cm-3), and → temperatures of 30-100 K (Snow & McCall, 2006, ARA&A 44, 367).

diffuse; → atomic; → gas.

diffuse galactic light
  نور ِ کهکشانی ِ پخشیده   
nur-e kahkašâni-ye paxšidé

Fr.: lumière galactique diffuse   

A minor component of galactic light resulting from the diffusion of starlight by → interstellar dust near the → galactic plane.

diffuse; → galactic; → light.

diffuse interstellar band (DIB)
  باند ِ پخشیده‌ی ِ اندر‌اختری   
bând-e paxšide-ye andaraxtari

Fr.: bande diffuse interstellaire   

Absorption features in the spectrum of stars identified in the ultraviolet, visible, and infrared regions. They have an interstellar origin, but despite extensive efforts, their carrier(s) have not yet been clearly identified. See also → Aromatic Infrared Bands; → polycyclic aromatic hydrocarbons.

diffuse; → interstellar; → band.

diffuse interstellar band carrier
  برنده‌ی ِ باند ِ پخشیده‌ی ِ اندر‌اختری   
barande-ye bând-e paxšide-ye andaraxtari

Fr.: porteur des bandes diffuses interstellaires   

The chemical element or composition that is supposedly at the origin of a → diffuse interstellar band (DIB).

diffuse; → interstellar; → band; → carrier.

diffuse interstellar cloud
  ابر ِ اندر‌اختری ِ پخشیده   
abr-e andaraxtari-ye paxšidé

Fr.: nuage interstellaire diffus   

An → interstellar cloud in which hydrogen is completely dissociated and which is less dense and dusty than → molecular clouds. In diffuse interstellar clouds photoabsorption of the background → ultraviolet (UV) radiation field is an important dissociating and ionizing process. Typical densities and temperatures of diffuse clouds are 102 to 103 cm-3 and 20 to 100 K respectively. Because of modest extinctions (≤ 1 mag), → photodissociation processes are important in diffuse clouds preventing the formation of larger molecules.

diffuse; → interstellar; → cloud.

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