An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < -ge Gal gal Gal gam gas Gau gen gen geo geo geo gia glo gol gra gra gra gra gre gri gui > >>

Number of Results: 438
gamma-ray astronomy
  اخترشناسی ِ پرتوها‌ی ِ گاما   
axtaršenâsi-ye partowhâ-ye gâmmâ (#)

Fr.: astronomie en rayons gamma   

The study of → gamma rays from → extraterrestrial → sources, especially → gamma-ray bursts.

gamma ray; → astronomy.

gamma-ray burst (GRB)
  بلک ِ پرتوها‌ی ِ گاما   
belk-e partowhâ-ye gâmmâ

Fr.: sursaut de rayons gamma   

An intense discharge of → gamma rays, which range in duration from tenth of a second to tens of seconds and occur from sources widely distributed over the sky. The radio wave → afterglow from the → burst can last more than a year, making long-term observations of the sources possible. The favored hypothesis is that they are produced by a relativistic jet created by the merger of two → compact objects (specifically two → neutron stars or a neutron star and a → black hole). Mergers of this kind are also expected to create significant quantities of neutron-rich radioactive species, whose decay should result in a faint → transient, known as a → kilonova, in the days following the burst. Indeed, it is speculated that this mechanism may be the predominant source of stable → r-process elements in the Universe. Recent calculations suggest that much of the kilonova energy should appear in the → near-infrared spectral range, because of the high optical opacity created by these heavy r-process elements (Tanvir et al., 2017, Nature 500, 547).

gamma rays; → burst.

gamma-ray burster
  بلکور ِ پرتو ِ گاما   
belkvar-e partow-e gâmmâ

Fr.: source à sursaut gamma   

The → object or → phenomenon at the origin of a → gamma-ray burst.

gamma ray; → burster.

gamma-ray source
  خن ِ پرتوهای ِ گاما   
xan-e partowhâ-ye gâmma

Fr.: source de rayons gamma   

1) An astronomical object that emits → gamma rays.
2) A radioactive material that emits gamma rays in a form that can be used in medical imaging.

gamma ray; → source.

Gamma2 Velorum
  گاما۲ بادبان   
gâmâ2 bâdbân

Fr.: γ2 Velorum   

The closest → Wolf-Rayet star, located at 336 → parsecs. Also known as HR 3207, HD 68273, and WR 111. γ2 Velorum is composed of a → WC8 component in a → close binary system with an → O star in a 78.5 day orbit (see, e.g., Lamberts et al., 2017, arXiv: 1701.01124).

Gamma, as in → Bayer designation; Velorum, genitive of → Vela.

Gamow barrier
  ورغه‌ی ِ گاموف   
varqe-ye Gâmof (#)

Fr.: barrière de Gamow   

In nuclear physics, a potential barrier near the surface of the nucleus that inhibits the release of alpha particles.

Gamow, after George Gamow (originally Georgiy Antonovich Gamov), the Ukrainian born theoretical physicist and cosmologist, who discovered quantum tunneling; → barrier.

Gamow condition
  بوتار ِ گاموف   
butâr-e Gamow

Fr.: condition de Gamow   

The constraint on the → baryon number density at T ~ 109 K in the early → expanding Universe. Gamow recognized that a key to the element buildup is the reaction n + p ↔ d + γ. Deuterium needs to be produced in sufficient abundance for higher elements to form, but if all → neutrons are immediately locked up into → deuterium, no higher elements can form either. The Gamow condition is expressed by nb<σv>t ~ 1, where nb is the baryon number density, σ is the cross section for the reaction at relative → velocity v, and t the expansion time-scale for the → Universe. This means that the time-scale for the above reaction is comparable to the expansion time. From this condition the baryon number density at the start of element buildup is found to be nb ~ (σvt)-1 ~ 1018 cm-3 at T = 109 K (P. J. E. Peebles, 2013, Discovery of the Hot Big Bang: What happened in 1948, arXiv.1310.2146).

Gamow barrier; → condition.

Gamow peak
  ستیغ ِ گاموف   
setiq-e Gâmof

Fr.: pic de Gamow   

In nuclear fusion, the product of the Maxwell-Boltzmann distribution with the tunnelling probability of the nuclei through their Coulomb barrier. This is the energy region where the reaction is more likely to take place: at higher energies, the number of particles becomes insignificant while at lower energies the tunnelling through the Coulomb barrier makes the reaction improbable.

Gamow barrier; → peak.

Ganymede (Jupiter III)

Fr.: Ganymède   

The seventh and largest of → Jupiter's known satellites. This → Galilean satellite has a diameter of 5270 km, slightly larger than Mercury, a mass about 1.48 × 1023 kg (about 2 Earth Moons); an → orbital period of 7.155 days, and an → eccentricity of e = 0.0015. It was discovered by Galileo and Marius in 1610. The mean → surface temperature of Ganymede is -160 °C. It is the only moon known to have a → magnetosphere.

In Gk. mythology, Ganymedes, a unusually beautiful prince of Troy who was abducted to Olympus by Zeus and made the cup-bearer of the gods.

gâf (#)

Fr.: division, lacune, trou   

An empty space or interval; interruption in continuity; a break or opening, as in a fence, wall. → Encke gap.

Gap, from O.N. gap "chasm," related to gapa "to gape."

Gâf, variant kâf "split, slit," stem of kâftan, kâvidan "to split; to dig," Mid./Mod.Pers. škâf- škâftan "to split, burst," Proto-Iranian *kap-, *kaf- "to split;" cf. Gk. skaptein "to dig;" L. cabere "to scratch, scrape," P.Gmc. *skabanan (Goth. skaban; Ger. schaben; E. shave). PIE base *(s)kep- "to cut, to scrape, to hack."

Garnet star
  ستاره‌ی ِ نارسنگ   
setâre-ye nârsang

Fr.: étoile Grenat   

A variable → red supergiant star of → spectral type M2 Ia in the → constellation → Cepheus. Also called → Mu Cephei. Its → apparent magnitude is usually about 4.5 and varies from 3.6 to 5.1. It is also a → triple star.

Garnet "a deep-red color," from the more or less transparent, usually red, silicate mineral that has a vitreous luster. So named by William Herschel from its unusual deep reddish tint. From O.Fr. grenat "garnet," from M.L. granatum, originally an adj., "of dark red color," probably abstracted from pomegranate, from M.L. pomum granatum "apple with many seeds," from pome "apple, fruit" + grenate "having grains."

Nârsang, from nâr, from anâr "pomegranate," from Mid.Pers. anâr "pomegranate" + sang, → stone.

gâz (#)

Fr.: gaz   

A substance whose physical state is such that it always occupies the whole of the space in which it is contained.

Gas, from Du. gas, probably from Gk. khaos "empty space," → chaos. The term gas was coined by the Belgian physician Jean-Baptiste van Helmont (1579-1644) to designate aerial spirits.

Gâz, loanword from Fr.

gas constant
  پایا‌ی ِ گاز‌ها   
pâyâ-ye gâzhâ (#)

Fr.: constante des gaz parfaits   

For a given quantity of an → ideal gas, the product of its → pressure and the → volume divided by the → absolute temperature (R = PV/T).

gas; → constant.

gas equation
  هموگش ِ گاز   
hamugeš-e gâz

Fr.: équation des gaz   

An equation that links the pressure and volume of a quantity of gas with the absolute temperature. For a gram-molecule of a perfect gas, PV = RT, where P = pressure, V = volume, T = absolute temperature, and R = the gas constant.

gas; → equation.

gas giant
  غولپیکر ِ گازی   
qulpeykar-e gâzi (#)

Fr.: géante gazeuse   

A → giant planet composed mainly of → hydrogen and → helium with → traces of → water, → methane, → ammonia, and other hydrogen compounds. Gas giants have a small rocky or metallic core. The core would be at high temperatures (as high as 20,000 K) and extreme pressures. There are four gas giants in our solar system: → Jupiter, → Saturn, → Uranus, and → Neptune. Another category of gas giants is → ice giants. Ice giants are also composed of small amounts of hydrogen and helium. However, they have high levels of what are called "ices." These ices include methane, water, and ammonia.

gas; → giant.

gas laser
  لیزر ِ گازی   
leyzer-e gâzi

Fr.: laser à gaz   

A kind of laser where the lasing medium is a gas or a mixture of gases that can be excited with an electric discharge. The first gas laser to operate successfully was built by A. Javan and William R. Bennette at the Bell Telephone Laboratories. This laser used a mixture of helium and neon as the active medium and produced a continuous beam rather than a series of pulses. This laser operated in the infrared region of the spectrum at 1.15 micrometres. A few years later Kumar Patel developed the CO2 laser.

gas; → laser.

gas metallicity
  فلزیگی ِ گاز   
felezigi-ye gâz

Fr.: métallicité de gaz   

The metallicity derived from observations of the gas component of a galaxy. It is mainly measured from optical → emission lines using primarily oxygen abundances. The gas → metallicity is one of the most important tools to investigate the evolutionary history of galaxies. The reason is that the gas metallicity of galaxies is basically determined by their star-formation history. Recent observational studies has allowed the investigation of the gas metallicity even in → high redshift beyond z = 1, such as → Lyman break galaxies, submillimeter-selected high-z galaxies, and so on. Such observational insights on the metallicity evolution of galaxies provide constraints on the theoretical understandings of the formation and the evolution of galaxies.

gas; → metallicity.

gas mixture
  آمیزه‌ی ِ گاز   
âmize-ye gâz

Fr.: mélange de gaz   

An aggregate of several different kinds of gases which do not react chemically under the conditions being considered. A gas mixture constitutes a homogeneous thermodynamical system.

gas; → mixture.

gas tail
  دنباله‌ی ِ گازی   
donbâle-ye gâzi

Fr.: queue de gaz   

The → ionized component of a → comet's → tail, driven nearly straight away from the → Sun Sun by the → solar wind. solar wind. Also called → ion tail, → plasma tail, and → Type I tail.

gas; → tail.

gas-poor galaxy
  کهکشان ِ کم‌گاز   
kahkešân-e kamgâz

Fr.: galaxie pauvre en gaz   

A galaxy which has a relatively low gas content. More specifically, a galaxy whose → baryonic matter is chiefly in the form of stars and has very little → interstellar matter.

gas; → poor; → galaxy.

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