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
high-excitation blob (HEB)
  ژیگ ِ پر-بر‌انگیزش   
žig-e por-barangizeš

Fr.:   

A rare class of → H II regions in the → Magellanic Clouds. In contrast to the typical H II regions of the Magellanic Clouds, which are extended structures (sizes of several arc minutes corresponding to more than 50 pc, powered by a large number of exciting stars), HEBs are very dense and small regions (~ 4" to 10" in diameter corresponding to ~ 1-3 pc). They have a higher degree of → excitation ([O III] 5007Å /Hβ) with respect to the typical H II regions, and are, in general, heavily affected by local → dust. They are powered by a relatively smaller number of → massive stars.

high; → excitation; → blob.

high-resolution observation
  نپاهش ِ مه-واگشود   
nepâheš-e mehvâgošud

Fr.: observation à haute résolution   

An observation that provides a particularly narrow, peaked image of a point source. → point spread function.

high; → resolution; → observation.

hole injection
  درشانش ِ سوراخ، ~ چاله   
daršâneš-e surâx, ~ câlé

Fr.: injection de trou   

The injection of holes in a semiconductor which can be produced by application of a sharp conducting point in contact with an n-type semiconductor.

hole; → injection.

holonomic system
  راژمان ِ هروداتیک   
râžmân-e harudâtik

Fr.: système holonomique   

A material system in which the → constraints can be expressed in the form of an equation relating the coordinates.

From Gk. → holo- "whole" + -nomic, related to nomos "law, managing, governing, custom," → -nomy; → system.

homogeneous linear differential equation
  هموگش ِ دگرسانه‌ای ِ خطی همگن   
hamugeš-e degarsâne-yi-ye xatti hamgen

Fr.: équation différentielle linéaire homogène   

A → linear differential equation if the right-hand member is zero, Q(x) = 0, on interval I.

homogeneous; → linear; → differential; → equation.

homonuclear molecule
  مولکول ِ هم‌هسته   
molekul-e ham-hasté

Fr.: molécule homonucléaire   

A molecule that is composed of only one type of → chemical element, e.g. the → molecular hydrogen and → ozone.

homo-; → nuclear; → molecule.

horizon
  افق   
ofoq (#)

Fr.: horizon   

1) An imaginary circle that delimits the sky and the Earth.
2) The fundamental great circle of the → horizon system, defined by the intersection of the → celestial sphere and a level plane passing through the observer. → celestial horizon.
3) In → Robertson-Walker models, the boundary separating objects already observed from those not yet observed, or the boundary separating objects observable from unobservable (J. Plebanski, A. Krasinski, 2006, An Introduction to General Relativity and Cosmology, Cambridge Univ. Press).
4) → cosmic horizon.
5) → event horizon.
See also:
apparent horizon, → artificial horizon, → astronomical horizon, → dip of the horizon, → distance to the horizon, → geometric horizon, → horizon coordinate system, → horizon problem, → horizon system, → particle horizon, → sea horizon, → sensible horizon, → sound horizon, → true horizon, → visible horizon.

From O.Fr. orizon, from orizonte, from L. horizontem (nom. horizon), from Gk. horizon kyklos "bounding circle," from horizein "bound, limit, divide, separate," from horos "boundary."

Ofoq, from Ar.

horizon coordinate system
  راژمان ِ هم‌آراهای ِ افقی   
râžmân-e hamârâhâ-ye ofoqi

Fr.: coordonnées horizontales   

The coordinate system based on the position of the observer. The horizontal plane is the fundamental plane and the coordinates are → altitude and → azimuth.

horizon; → coordinate; → system.

horizon problem
  پراسه‌ی ِ افق   
parâse-ye ofoq

Fr.: problème de l'horizon   

A problem with the standard cosmological model of the Big Bang related to the observational fact that regions of the Universe that are separated by vast distances nevertheless have nearly identical properties such as temperature. This contradicts the fact that light moves with a finite speed and, as a result, certain events which occur in the Universe are completely independent of each other. Inflationary cosmology offers a possible solution.

horizon; → problem.

horizon system
  راژمان ِ افقی   
râžmân-e ofoqi

Fr.: coordonnées horizontales   

Same as → horizon coordinate system.

horizon; → system.

horizontal
  افقی   
ofoqi (#)

Fr.: horizontal   

1) Of or pertaining to the → horizon.
2) At right angles to the → vertical; parallel to level ground.
See also:
blue horizontal branch star, → extreme horizontal branch star, → field horizontal branch star, → horizontal branch, → horizontal branch star, → horizontal eclipse, → horizontal parallax, → horizontal refraction, → red horizontal branch star, → supra-horizontal branch star, → zero age horizontal branch star.

From → horizon + → -al.

horizontal branch (HB)
  شاخه‌ی ِ افقی   
šâxe-ye ofoqi (#)

Fr.: branche horizontale   

A set of roughly horizontal points in the → Hertzsprung-Russell diagram of a typical → globular cluster. It displays a stage of stellar evolution which immediately follows the → red giant branch (RGB) in stars with an initial mass < 1.2 Msun. When the star's ascent of the RGB is terminated by the → helium flash, it moves down to the HB. The star's → effective temperature on the HB is higher than it was on the RGB, but the luminosity is considerably less than at the helium flash. Usually HB stars have two energy sources: in addition to the → helium burning in their cores, they experience → hydrogen fusion in a surrounding shell. The thickness of the shell determines the color of the HB stars. A thin shell, involving low → opacity, makes the star look blue. The HB domain encompasses a very large effective temperature range with several members: → extreme HB, → blue HB, → RR Lyrae, → red HB, and → red clump stars. The locations depend on many parameters, including stellar mass, metallicity, age, helium abundance, and rotation.

horizontal; → branch.

horizontal branch star
  ستاره‌ی ِ شاخه‌ی ِ افقی   
setâre-ye šâxe-ye ofoqi

Fr.: étoile de la branche horizontale   

A star lying on the → horizontal branch.

horizontal; → branch; → star.

horizontal eclipse
  ماه‌گرفت ِ افقی   
mâhgereft-e ofoqi

Fr.: selenelion   

A type of → lunar eclipse that occurs when both the Sun and the eclipsed Moon can be observed at the same time. This is possible only when lunar eclipse occurs just before sunset or just after sunrise. At that case, both bodies will appear just above the horizon at nearly opposite points in the sky. Also called → selenelion and → selenehelion.

horizontal; → eclipse.

horizontal parallax
  دیدگشت ِ افقی   
didgašt-e ofoqi

Fr.: parallaxe horizontale   

The angle under which the radius of the Earth at the place of observation would be seen from a celestial body when it is in the horizon (at the instant of rising or setting). The amount varies with the latitude since the Earth is not exactly spherical, and is greatest at equator.

horizontal; → parallax.

horizontal refraction
  شکست ِ افقی   
šekast-e ofoqi (#)

Fr.: réfraction horizontale   

The angular distance of an object below the horizon when it appears to lie on the horizon.

horizontal; → refraction.

horizontal scaling
  مرپلش ِ افقی   
marpeleš- ofoqi

Fr.:   

In computer science, a scaling in which the processing power is increased/decreased by adding/removing nodes with similar resources. See also → vertical scaling.

horizontal; → scaling.

hot accretion flow
  تچان ِ فربال ِ داغ   
tacân-e farbâl-e dâq

Fr.: écoulement d'accrétion chaud   

A type of → accretion flow by a → compact object such as a → black hole which has a high → virial temperature, is → optically thick, and occurs at lower mass → accretion rates compared with → cold accretion flows. In a hot accretion flow with a very low mass accretion rate, the electron mean free path is very large, and so the accreting → plasma is nearly collisionless. In this type of accretion flow, thermal conduction transports the energy from the inner to the outer regions. As the gas temperature in the outer regions can be increased above the → virial temperature , the gas in the outer regions can escape from the gravitational potential of the central black hole and form outflows, significantly decreasing the mass accretion rate.

cold; → accretion; → flow.

hot electron diode
  دیود ِ الکترون ِ داغ   
diod-e elektron-e dâq

Fr.:diode à électrons chauds   

Same as → Schottky diode

hot; → electron; → diode.

Hubble classification
  رده‌بندی ِ هابل   
radebandi-ye Hubble (#)

Fr.: classification de Hubble   

The classification of galaxies according to their visual appearance into four basic types suggested by E. Hubble: → ellipticals (E), → spirals (S), → barred spirals (SB), and → irregulars (Ir). Later on a separate class of → lenticulars (S0) was appended as an intermediate type between ellipticals and spirals. The sequence starts with round elliptical galaxies (E0). Flatter galaxies are arranged following a number which is calculated from the ratio (a - b)/a, where a and b are the major and minor axes as measured on the sky. Ellipticals are divided into eight categories (E0, E1, ..., E7). Beyond E7 a clear disk is apparent in the lenticular (S0) galaxies. The sequence then splits into two parallel branches of disk galaxies showing spiral structure: ordinary spirals, S, and barred spirals, SB. The spiral and barred types are subdivided into Sa, Sb, Sc, and SBa, SBb, SBc, respectively. Along the sequence from Sa to Sc, the central bulge becomes smaller, while the spiral arms become more and more paramount. The original, erroneous idea that such arrangement of the galaxies might represent an evolutionary sequence led to the ellipticals being referred to as early-type galaxies, and the spirals and Irr I irregulars as late-type galaxies. See also → dwarf galaxy, → dwarf elliptical galaxy, → dwarf spheroidal galaxy.

Hubble; → classification.

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