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.
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.
→ differential; → rotation.
differentially rotating system
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.
To perceive or show the difference in or between.
M.L. differentiatus "distinguished," p.p. of differentiare.
Degarsânidan, verbal form of → difference.
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.
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.
Verbal noun of → differentiate.
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-.
Verbal form of → 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
with the primary wavefront as well as with each other to form a
→ diffraction pattern.
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.
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.
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; parâš→ diffraction.
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.
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 karân→ boundary + -mand possession suffix; parâš→ diffraction.
1) paxšidan (#); 2) paxšidé (#)
Fr.: 1) diffuser; 2) diffus
1a) To pour out, to spread in all directions.
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
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 galactic light
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 interstellar band (DIB)
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
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
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.