An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



Number of Results: 16 Search : shell
circumstellar shell
  پوسته‌ی ِ پیراستاره‌ای   
puste-ye pirâsetâreyi

Fr.: coquille circumstellaire   

A shell of dust, molecules, and neutral gas around an evolved star resulting from an intensive mass loss phase, such as the asymptotic giant branch phase for low- and intermediate mass stars and LBVs or supernovae for massive stars.

circumstellar; → shell.

double shell burning
  سوزش ِ پوسته‌ی ِ دوتایی   
suzeš-e puste-ye dotâyi

Fr.: combustion double coquille   

A situation in the evolution of an → asymptotic giant branch star whereby both hydrogen and helium shells provide energy alternatively. As the burning → helium shell approaches the hydrogen-helium discontinuity, its luminosity decreases because it runs out of the fuel. As a consequence, the layers above contract in response, thus heating the extinguished → hydrogen shell until it is re-ignited. However, the shells do not burn at the same rate: the He burning shell becomes thermally unstable and undergoes periodic → thermal pulses.

double; → shell; → burning.

Dyson shell
  پوسته‌ی ِ دایسون   
puste-ye Dyson

Fr.: couche de Dyson   

Dyson sphere.

Dyson; → shell.

electron shell
  پوسته‌ی ِ الکترونی   
puste-ye elekroni (#)

Fr.: couche éléctronique   

Any of up to seven energy levels on which an electron may exist within an atom, the energies of the electrons on the same level being equal and on different levels being unequal. The number of electrons permitted in a shell is equal to 2n2. A shell contains n2 orbitals, and n subshells.

electron; → shell.

helium shell burning
  سوزش ِ پوسته‌ی ِ هلیوم   
suzeš-e puste-ye heliom

Fr.: combustion de la coquille d'hélium   

A stage in the evolution of an → asymptotic giant branch star, when all the helium in the core is fused into carbon and oxygen. No more fusion takes place in the core, and as a result the core contracts. The core contraction generates a sufficient temperature for fusing the surrounding layers of helium. Since helium shell burning is unstable, it causes → helium shell flashes.

helium; → shell; → burning.

helium shell flash
  درخش ِ پوسته‌ی ِ هلیومی   
deraxš-e puste-ye heliomi

Fr.: flash de la couche d'hélium   

A violent outburst of energy that occurs periodically in an → asymptotic giant branch star. It occurs when helium is being burnt in a thin shell surrounding the inner dense core of carbon and oxygen. → Helium shell burning is unstable, producing energy mainly in short intense flashes. The shell flash causes considerable expansion of the star followed by collapse, thus setting up deep convection. As a consequence, the → convective zone in the outer part of the star goes deeper and may → dredge-up carbon to the surface. See also → late thermal pulse; → very late thermal pulse; → AGB final thermal pulse.

helium; → shell; → flash.

hydrogen shell burning
  سوزش ِ پوسته‌ی ِ هیدروژن   
suzeš-e puste-ye hidrožen

Fr.: combustion de la coquille d'hydrogène   

A phase in the life of a star that has left the → main sequence. When no more hydrogen is available in the core, the core will start to contract as it is no longer releasing the necessary energy whose pressure supports the surrounding layers. As a result of this contraction, gravitational energy is converted into thermal energy and the temperature will rise. Therefore a shell of unprocessed material surrounding the original core will be heated sufficiently for hydrogen burning to start. During the evolution of → asymptotic giant branch stars hydrogen shell burning occurs alternatively with helium shell burning. → double shell burning.

hydrogen; → shell; → burning.

Newton's shell theorem
  فربین ِ پوسته‌ی ِ نیوتن   
farbin-e puste-ye Newton

Fr.: théorème de Newton   

In classical mechanics, an analytical method applied to a material sphere to determine the gravitational field at a point outside or inside the sphere. Newton's shell theorem states that: 1) The gravitational field outside a uniform spherical shell (i.e. a hollow ball) is the same as if the entire mass of the shell is concentrated at the center of the sphere. 2) The gravitational field inside the spherical shell is zero, regardless of the location within the shell. 3) Inside a solid sphere of constant density, the gravitational force varies linearly with distance from the center, being zero at the center of mass. For the relativistic generalization of this theorem, see → Birkhoff's theorem.

Newton; → shell; → theorem.

  صدف، کلاچک   
sadaf (#), kelâcak (#)

Fr.: coquille   

The hard shell of a marine mollusk.

sea; → shell.

Sadaf, loan from Ar. Kelâcak from Tabari, variant kelâcin, cf. Gilaki guš kuli. The component kel-, kul might be related to PIE *qarq- "to be hard," → crab.

pusté (#)

Fr.: coquille; couche   

1) General: A relatively thin external form covering a hollow space.
2) Physics: → electron shell.
3) → seashell.
4) Astro.: → shell burning; → shell galaxy; → shell star; → shellular rotation; → SNR shell.

M.E.; O.E. sciell, scill "seashell, eggshell," related to O.E. scealu "shell, husk;" cf. W.Fris. skyl "peel, rind," M.L.G. schelle "rind, egg shell," Goth. skalja "tile;" PIE base *(s)kel- "to cut, cleave."

Pusté "shell," from pust "skin;" Mid.Pers. pôst "skin;" O.Pers. pavastā- "thin clay envelope used to protect unbaked clay tablets;" Av. pastô-, in pastô.fraθanhəm "of the breadth of the skin;" Skt. pavásta- "cover," Proto-Indo-Iranian *pauastā- "cloth."

shell burning
  سوزش ِ پوسته   
suzeš-e pusté

Fr.: combustion en couche   

The nuclear reactions in a shell around a star's core that continue after the fuel in the core itself has been exhausted. As the fuel is progressively exhausted, the shell moves outward until it enters regions too cool for the reactions to continue. For example, after the exhaustion of hydrogen in the core, helium burning might take place in the core with a shell of hydrogen burning surrounding it. Stars may have more than one region of shell burning during their stellar evolution, each shell with its own nuclear reactions. → hydrogen shell burning; → helium shell burning.

shell; → burning.

shell galaxy
  کهکشان ِ پوسته‌دار   
kahkešân-e pustedâr

Fr.: galaxie en coquille   

An elliptical galaxy that is surrounded by thin shells of stars which are thought to have been ejected during a galaxy merger. Shell galaxies are different from ring galaxies in that the shells are much further away from the galaxy's centre and much fainter than the rings. Spectroscopy of the stars in the shell show that they are old whereas the stars in a ring galaxy are young.

shell; → galaxy.

shell star
  ستاره‌ی ِ پوسته‌دار   
setâre-ye pustedâr

Fr.: étoile à enveloppe   

A main-sequence star, usually of spectral class B to F, whose spectrum shows bright emission lines superimposed on the normal absorption lines. The emission spectrum is explained by the presence of a circumstellar shell of gas surrounding the star at the equator. Shell stars are fast rotators.

shell; → star.

shellular rotation
  چرخش ِ پوسته‌ای   
carxeš-e puste-yi

Fr.: rotation coquillaire   

A rotation mode in which internal rotation of a star depends essentially on depth and little on latitude: Ω(r,θ) = Ω(r), where r is the mean distance to the stellar center of the considered level surface (or → isobar). This particular mode was introduced by J.-P. Zahn (1992, A&A 265, 115) to simplify the treatment of rotational → mixing, but also on more physical grounds. Indeed differential rotation tends to be smoothed out in latitude through → shear turbulence. See also → von Zeipel theorem; → meridional circulation .

Shellular, the structure of this term is not clear; it may be a combination of → shell (referring to star's assumed division in differentially rotating concentric shells) + (circ)ular, → circular. The first bibliographic occurrence of shellular is seemingly in Ghosal & Spiegel (1991, On the Thermonuclear Convection: I. Shellular Instability, Geophys. Astrophys. Fluid Dyn. 61, 161). However, surprisingly the term appears only in the title, and nowhere in the body of the article; → rotation.

Carxeš, → rotation; puste-yi, adj. of pusté, → shell.

SNR shell
  پوسته‌ی ِ بازمانده‌ی ِ اَبَر-نوختر   
pustey-e bâzmânde-ye abar-now-axtar

Fr.: coquille de reste de supernova   

A ring-like structure of swept-up → gas and → dust around a → supernova remnant. See also: → free expansion phase, → Sedov-Taylor phase, → snowplow phase.

supernova remnant (SNR); → shell.


Fr.: sous couche   

A set of electrons with the same angular momentum quantum number, denote l. The number of electrons permitted in a subshell is equal to 2l + 1.

sub- + → shell.