An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 1965 Search : ion
gravitational redshift
  سرخ‌کیب ِ گرانشی   
sorxkib-e gerâneši

Fr.: décalage vers le rouge gravitationnel   

The change in the wavelength or frequency of electromagnetic radiation in a gravitational field predicted by general relativity.

gravitational; → redshift.

gravitational settling
  نیاشش ِ گرانشی   
niyâšeš-e gerâneši

Fr.: décantation par gravité   

A physical process occurring in → stellar atmospheres whereby in a very stable atmosphere → heavy elements are gravitationally pulled down preferentially. If such an atmosphere is stable for long periods of time, the → absorption lines of heavy elements may therefore become very weak. Observationally, the star seems to contain only → hydrogen and → helium. Gravitational settling takes place in the Sun at the bottom of the outer → convective zone where helium is dragged down, leading to a surface He abundant smaller than the cosmic value. It occurs also in the atmospheres of → brown dwarfs and → planets. See also → radiative levitation, → element diffusion, → thermal diffusion.

gravitational; → settling.

gravitational slingshot
  فلاخن ِ گرانشی   
falâxan-e gerâneši

Fr.: fronde gravitationnelle   

Same as → gravity assist.

gravitational; slingshot, from sling, from M.E. slyngen, from O.N. slyngva "to sling, fling" + shot, from M.E., from O.E. sc(e)ot, (ge)sceot; cf. Ger. Schoss, Geschoss.

Falâxan "sling;" from Av. fradaxšana- "sling," fradaxšanya- "sling, sling-stone;" → gravitational.

gravitational wave
  موج ِ گرانشی   
mowj-e gerâneši (#)

Fr.: ondes gravitationnelles   

A → space-time oscillation created by the motion of matter, as predicted by Einstein's → general relativity. When an object accelerates, it creates ripples in space-time, just like a boat causes ripples in a lake. Gravitational waves are extremely weak even for the most massive objects like → supermassive black holes. They had been inferred from observing a → binary pulsar in which the components slow down, due to losing energy from emitting gravitational waves. Gravitational waves were directly detected for the first time on September 14, 2015 by the → Laser Interferometer Gravitational-Wave Observatory (LIGO) (Abbott et al., 2016, Phys. Rev. Lett. 116, 061102). Since then several other events have been detected by LIGO and → Laser Interferometer Space Antenna (LISA). The Nobel Prize in physics 2017 was awarded to three physicists who had leading roles in the first detection of gravitational waves using LIGO. They were Rainer Weiss (MIT), Barry C. Barish, and Kip S. Thorne (both Caltech).
2) Not to be confounded with → gravity wave.

gravitational; → wave.

gravitational-field theory
  نگره‌ی ِ میدان ِ گرانشی   
negare-ye meydân-e gerâneši (#)

Fr.: théorie de champ gravitationnel   

A theory that treats gravity as a field rather than a force acting at a distance.

gravitational; → field.

gravitationally bound
  گرانشانه بندیده   
gerânešâné bandidé

Fr.: gravitationnellement lié   

Objects held in orbit about each other by their → gravitational attraction. Such objects are part of a → bound system.

gravitational; → bound.

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.

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.


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").

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.

Hamiltonian function
  کریای ِ هامیلتون   
karyâ-ye Hâmilton

Fr.: fonction de Hamilton   

A function that describes the motion of a → dynamical system in terms of the → Lagrangian function, → generalized coordinates, → generalized momenta, and time. For a → holonomic system having n degrees of freedom, the Hamiltonian function is of the form: H = Σpiq.i - L(qi,q.i,t) (summed from i = 1 to n), where L is the Lagrangian function. If L does not depend explicitly on time, the system is said to be → conservative and H is the total energy of the system. The Hamiltonian function plays a major role in the study of mechanical systems. Also called → Hamiltonian.

Introduced in 1835 by the Irish mathematician and physicist William Rowan Hamilton (1805-1865); → function.

harmonic motion
  جنبش ِ هماهنگ   
jonbeš-e hamâhang (#)

Fr.: mouvement harmonique   

A motion that repeats itself in equal intervals of time (also called periodic motion).

harmonic; → motion.

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