An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 3106 Search : on
gravity darkening exponent
  نمای ِ تاریکش ِ گرانشی   
nemâ-ye târikeš-e gerâneši

Fr.: exposant de l'assombrissement gravitationnel   

The exponent appearing in the power law that describes the → effective temperature of a → rotating star as a function of the → effective gravity, as deduced from the → von Zeipel theorem or law. Generalizing this law, the effective temperature is usually expressed as Teff∝ geffβ, where β is the gravity darkening exponent with a value of 0.25. It has, however, been shown that the relation between the effective temperature and gravity is not exactly a power law. Moreover, the value of β = 0.25 is appropriate only in the limit of slow rotators and is smaller for fast rotating stars (Espinosa Lara & Rieutord, 2011, A&A 533, A43).

gravity; → darkening; → exponent.

grazing occultation
  فروپوشانش ِ برمژنده   
forupušâneš-e barmažandé

Fr.: occultation rasante   

A special type of occultation that occurs when the star appears to pass tangentially on the → edge of the → Moon.

grazing; → occultation.

greatest eastern elongation
  بزرگترین درازش ِ خاوری   
bozorgtarin derâzeš-e xâvari

Fr.: plus grande élongation est   

The Greatest → elongation of an inferior planet occurring after sunset.

Superlative of → great; → eastern; → elongation.

greatest elongation
  بزرگترین درازش   
bozorgtarin derâzeš

Fr.: plus grande élongationt   

The largest → elongation of an inferior planet from the Sun. It may be → greatest eastern elongation or → greatest western elongation. The greatest elongation of Mercury is about 28°, and thus Mercury can only be observed 112 minutes after sunset or before sunrise. For Venus, it is about 47°, making it visible at most about 3 hours after sunset or before sunrise.

Superlative of → great; → eastern; → elongation.

greatest western elongation
  بزرگترین درازش ِ باختری   
bozorgtarin derâzeš-e bâxtari

Fr.: plus grande élongation ouest   

The Greatest → elongation of an inferior planet occurring before sunrise.

Superlative of → great; → western; → elongation.

ground-based observation
  نپاهش از زمین   
nepâheš az zamin

Fr.: observation au sol   

An astronomical observation carried out using a telescope on Earth, as opposed to that from an orbiting satellite.

ground; based, adj. of base, from O.Fr. bas, from L. basis "foundation," from Gk. basis "step, pedestal," from bainein "to step;" → observation.

Nepâheš, → observation; az "from," → ex-; zamin, → ground.

Gunn-Peterson effect
  ا ُسکر ِ گان-پیترسون   
oskar-e Gunn-Peterson

Fr.: effet Gunn-Peterson   

The continuum trough observed in the spectra of high redshift quasars (z> 6) at the blue wing of their Lyman-alpha emission line (1216 Å). It is explained by the scattering of the radiation of the quasar by intergalactic neutral hydrogen on the line of sight. Because of the cosmological expansion, the quasar line is redshifted with respect to the continuum trough. The Gunn-Peterson opacity increases rapidly with redshift. It is interpreted as a strong evidence for the reionization of the Universe around z = 6.

After James E. Gunn and Bruce A. Peterson who predicted the effect in 1965; → effect.

H I region
  ناحیه‌ی ِ H I   
nâhiye-ye H I

Fr.: région H I   

A region of neutral (atomic) hydrogen in interstellar space. At least 95 percent of interstellar hydrogen is H I. It emits radio waves that are 21 cm long.

H I; → region

H II region
  ناحیه‌ی ِ H II   
nâhiye-ye H II

Fr.: région H II   

A type of → emission nebulae composed of very hot gas (about 104 K), mainly ionized hydrogen, created by the ultraviolet radiation of → massive stars. H II regions originate when O or early-type stars, born in → giant molecular clouds, start heating up the cold gas, causing it to become → ionized and "glow". The effective temperatures of the → exciting stars are in the range 3 x 104 to 5 x 104 K, and throughout the nebula hydrogen is ionized. Helium is → singly ionized, and other elements are mostly singly or → doubly ionized. Typical densities in the H II region are of the order 10 to 102 cm-3, ranging as high as 104 cm-3. Internal motions occur in the gas with velocities of order 10 km s-1. The spectra of H II regions are mainly composed of strong → H Irecombination lines and → forbidden lines such as [O III], [O II], [N II]. See also → ionization-bounded H II region; → density-bounded H II region; → compact H II region; → ultracompact H II region.

H II; → region

H II region luminosity
  تابندگی ِ ناحیه‌ی ِ H II   
tâbandegi-ye nâhiye-ye H II

Fr.: luminosité de région H II   

The total number of → Lyman continuum photons emitted by an → H II region. It is usually derived using → radio continuum observations which are less affected by → interstellar extinction. The measured value is often a lower limit because of photon leakage from the H II region and absorption. See also → density-bounded H II region.

H II; → region; → luminosity.

habitable zone (HZ)
  زُنار ِ زیست‌پذیر   
zonâr-e zistpazir

Fr.: zone habitable   

A zone around a → star where the → temperature would be in the range 0-100 °C to sustain → liquid water on the surface of rocky planets (or sufficiently large moons). Water is thought to be a necessary component to the → formation and evolution of Earth-type life. This zone depends on the parent star's luminosity and distance; it will be farther from hotter stars. A more accurate definition of HZ needs to include other factors, such as orbital → eccentricity, heat sources other than stellar irradiation, and atmospheric properties. Same as → circumstellar habitable zone; → ecosphere.

habitable; → zone.

hadron
  هادرون   
hâdron (#)

Fr.: hadron   

Any elementary particle which experiences the strong nuclear force. There are two sorts of hadrons: mesons, which have zero spin, and baryons, which have spin 1/2 or 3/2.

Hadron, from Gk. hadr(os) "thick, bulky" + -on a suffix used in the names of subatomic particles (gluon, meson, neutron), quanta (photon, graviton), and other minimal entities or components (magneton).

hadron era
  دوران ِ هادرونی   
dowrân-e hâdroni

Fr.: ère hadronique   

The interval lasting until some 10-5 seconds after the Big Bang when the Universe was dominated by radiation and its temperature was around 1015 kelvins. It is preceded by → Planck era and followed by → lepton era.

hadron; → era.

hadronic
  هادرونی   
hâdroni (#)

Fr.: hadronique   

Of or related to → hadrons.

hadron; → -ic.

hadronic matter
  ماده‌ی ِ هادرونی   
mâde-ye hâdroni (#)

Fr.: matière hadronique   

Ordinary matter composed of → hadrons.

hadronic; → matter.

halation
  هاله‌گیری   
hâlegiri

Fr.: halo   

1) In a cathode-ray tube, the glow surrounding a bright spot that appears on the fluorescent screen as the result of the screen's light being reflected by the front and rear surfaces of the tube's face.
2) The effect in which a halo appears around the image of a bright object recorded on a photographic film or plate. It is produced by the fan-like pattern of light reflected through the emulsion by the medium's backing material.

Halation, from hal(o), → halo + -ation a combination of -ate and -ion, used to form nouns from stems in -ate.

Hâlegiri, from hâlé, → halo + giri, verbal noun of gereftan "to take, seize" (Mid.Pers. griftan, Av./O.Pers. grab- "to take, seize," cf. Skt. grah-, grabh- "to seize, take," graha "seizing, holding, perceiving," M.L.G. grabben "to grab," from P.Gmc. *grab, E. grab "to take or grasp suddenly;" PIE base *ghrebh- "to seize").

half moon
  نیمه‌مانگ، نیمه‌ماه   
nime mâng, nime mâh (#)

Fr.: demi-lune   

The moon when, at either quadrature, half its disk is illuminated.

half; → moon.

halo occupation distribution (HOD)
  واباژش ِ هگش ِ هاله   
vâbâžeš-e hageš-e hâlé

Fr.: distribution d'occupation de halo   

The → probability distribution of the → number of galaxies that a host → dark matter halo of a given mass contains. HOD is a powerful theoretical frame to populate dark matter halos with luminous galaxies. More specifically, it describes the bias between galaxies and dark matter by specifying (a) the probability P(N|M) that a halo of → virial mass M contains N galaxies of a particular class and (b) the relative spatial and velocity distributions of galaxies and dark matter within halos.

halo; → occupation; → distribution.

halo population
  پُرینش ِ هاله   
porineš-e hâlé

Fr.: population du halo   

Old stars with very low metallicities (→ metallicity) found in the → halo of the Galaxy. Also called → population II star.

halo; → population.

Hamilton's equation
  هموگش ِ هامیلتون   
hamugeš-e Hamilton

Fr.: équation de Hamilton   

One of a set of equations that describe the motion of a → dynamical system in terms of the → Hamiltonian function and the → generalized coordinates. For a → holonomic system with n degrees of freedom, Hamilton's equations are expressed by: q.i = ∂H/∂pi and p.i = - ∂H/∂qi, i = 1, ..., n.

Hamiltonian function; → equation.

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