An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 1286
steady state theory
  نگره‌ی ِ حالت ِ پایا   
negare-ye hâlat-e pâyâ

Fr.: théorie de l'état stationnaire   

A → cosmological model according to which the → Universe has no beginning and no end and maintains the same mean density, in spite of its observed expansion, by the continual creation of matter throughout all space. The theory was first put forward by Sir James Jeans in about 1920 and again in revised form in 1948 by Hermann Bondi and Thomas Gold. It was further developed by Sir Fred Hoyle to deal with problems that had arisen in connection with the alternative → Big Bang model. Observations since the 1950s have produced much evidence contradictory to the steady state theory and supportive of the Big Bang model. More specifically, the steady state theory attributed the → cosmic microwave background to → thermal radiation from → dust clouds, but this cannot account for a single → blackbody spectrum. Moreover, the steady state theory lacked a plausible mechanism for the creation of matter in space. See also → perfect cosmological principle.

steady; → state; → theory.

boxâr (#)

Fr.: vapeur   

The vapor into which water is changed when boiled.

From M.E. steme, O.E. steam; cognate with Du. stoom, of unknown origin.

Boxâr, → vapor.

steam engine
  ماشین ِ بخار   
mâšin-e boxâr (#)

Fr.: machine à vapeur   

An engine in which the energy of hot → steam is converted into → mechanical power, especially an engine in which the force of expanding steam is used to drive one or more → pistons. The source of the steam is typically external to the part of the machine that converts the steam energy into → mechanical energy (

steam; → engine.

pulâd (#)

Fr.: acier   

A strong → alloy of → iron containing up to 1.5 percent → carbon along with small amounts of other → chemical elements such as → manganese, → chromium, → nickel, and so forth.

O.E. style; cf. O.S. stehli, O.N., M.L.G. stal, Dan. staal, Swed. stål, M.Du. stael, Du. staal, O.H.G. stahal, Ger. Stahl.

Pulâd, variant fulâd, from Mid.Pers. pôlâwad, pôlâvat, loaned in Arm. polopat, polovat, maybe related to Skt. pavīra- "a weapon with metallic point, a spear, a lance."

qapân (#)

Fr.: balance romaine   

A balance used for weighing loads that has a two beams of different lengths. The shorter beam has a hook or the like for holding the object to be weighed and the longer one supports a movable counterpoise that slides to attain a balance.

steel; yard, from M.E. yard(e), O.E. gerd "straight twig;" cognate with Du. gard, Ger. Gerte "rod."

Qapân, from kapân "a large balance with one scale, being kept in equilibrium by a weight on the other end of the beam, a lever balance" (Steingass).

Stefan-Boltzmann constant
  پایای ِ اشتفان-بولتسمن   
pâyâ-ye Stefan-Boltzmann

Fr.: constante de Stefan-Boltzmann   

The constant of proportionality present in the → Stefan-Boltzmann law. It is equal to σ = 5.670 × 10-8 W m-2 K-4 or 5.670 × 10-5 erg cm-2 s-1 K-4.

Stefan-Boltzmann law; → constant.

Stefan-Boltzmann law
  قانون ِ اشتفان-بولتسمن   
qânun-e Stefan-Boltzmann

Fr.: loi de Stefan-Boltzmann   

The flux of radiation from a blackbody is proportional to the fourth power of its absolute temperature: L = 4πR2σT4. Also known as Stefan's law.

Ludwig Eduard Boltzmann (1844-1906), an Austrian physicist, who made important contributions in the fields of statistical mechanics and statistical thermodynamics and Josef Stefan (1835-1893), an Austrian physicist; → law.

Steiner's theorem
  فربین ِ اشتاینر   
farbin-e Steiner

Fr.: théorème de Steiner   

The → moment of inertia of a body about an arbitrary axis x' is equal to the sum of its moment of inertia about axis x, passing through the center of mass of the body and parallel to axis x', and the product of the mass M of the body by the square of the distance d between axes x and x': Ix' = Ix + Md2. Same as → parallel axis theorem.

Named after Jakop Steiner (1796-1863), a Swiss mathematician who derived this statement; → theorem.

  ۲۸۶۷ اشتاینس   
2867 Šteins

Fr.: 2867 Šteins   

A small → main belt  → asteroid of size 5.9 x 4 km, discovered in 1969 by N. S. Chernykh. It was visited by the → Rosetta space probe in 2008.

Named after Karlis Šteins (1911-1983), a Latvian and Soviet astronomer.

stellar aberration
  بیراهش ِ ستاره‌ای   
birâheš-e setâre-yi

Fr.: aberration stellaire   

Same as → aberration of starlight .

stellar; → aberratio.

stellar association
  آهزش ِ ستاره‌ای   
âhazeš-e setâre-yi

Fr.: association stellaire   

1) A large, loose grouping of 10 to 1000 stars that are of similar spectral type and share a common origin. The members move together through space, but have become gravitationally → unbound. Stellar associations are primarily identified by their common movement vectors and ages. → OB association; → T association; → R association.
2) An → unbound stellar agglomeration for which the age of the stars is smaller than the → crossing time (Giels & Portegies Zwart, 2010, MNRAS Letters, astro-ph/1010.1720). See also → star cluster.

The concept of stellar association was first introduced by Viktor A. Ambartsumian (1908-1996), Armenian astrophysicist (1947, Stellar Evolution and Astrophysics, Armenian Acad. of Sci.; German translation, Abhandl. Sowjetischen Astron. Ser. 1. 33, 1951). → stellar; → association.

stellar astronomy
  اخترشناسی ِ ستاره‌ای   
axtaršenâsi-ye setâreyi (#)

Fr.: astronomie stellaire   

The branch of astronomy that deals with the study of stars, their physical properties, formation, and evolution. Same as → stellar astrophysics and → stellar physics.

stellar; → astronomy.

stellar astrophysics
  اخترفیزیک ِ ستاره‌ای   
axtarfizik-e setâre-yi

Fr.: astrophysique stellaire   

The field of → astrophysics concerned with the study of the physical characteristics of stars, more specifically their → internal structure, physical processes taking place in their interiors, atmospheres, → stellar winds, → mass loss, interaction with the → interstellar medium, as well as the physical laws governing → star formation. Same as → stellar physics and → stellar astronomy.

stellar; → astrophysics.

stellar atmosphere
  جوّ ِ ستاره‌ای، هواسپهر ِ ~   
javv-e setâre-yi, havâsephre ~

Fr.: atmosphère stellaire   

The outer envelope of gas and plasma that surrounds a star; characterized by pressure, temperature, density, chemical composition, and opacity at varying altitudes.

stellar; → atmosphere.

stellar atmosphere model
  مدل ِ جو ِ ستاره   
model-e javv-e setâré

Fr.: modèle d'atmosphère stellaire   

A model that computes the radiation field crossing the boundary layers of a star at all frequencies. The parameters used for the characterization of a stellar atmosphere model are: → effective temperature, → surface gravity, and → metallicity.

stellar; → atmosphere; → model.

stellar black hole
  سیه‌چال ِ ستاره‌ای   
siyah câl-e setâre-yi

Fr.: trou noir stellaire   

A → black hole with a mass in the range 3-30 → solar masses representing the end-product of → massive star evolution. Since → neutron stars cannot have masses larger than 3 solar masses, compact objects more massive than this must be black holes. There is good observational evidence for the existence of stellar black holes, based in particular on dynamical measurements of the masses of compact objects in → transient X-ray sources. Same as → stellar-mass black hole.

stellar; → black; → hole.

stellar creation function
  کریای ِ آفرینش ِ ستارگان   
karyâ-ye âfarineš-e setâregân

Fr.: fonction de création stellaire   

The number of stars born per unit area in the mass range log M to log M + d log M during the time interval t to t + dt. The integration of the creation function over time gives the → present-day mass function (Miller & Scalo, 1797, ApJSS 41, 513).

stellar; → creation; → function.

stellar cusp
  تیزه‌ی ِ ستاره‌ای   
tize-ye setâre-yi

Fr.: cuspide stellaire   

A steeply rising radial profile (→ cusp) in the number density of stars in the central region of a galaxy resulting from the gravitational influence of a central → supermassive black hole, as predicted by theoretical models. An important assumption of all cusp formation models is that the stellar cluster is in dynamical equilibrium in the black hole potential. This radial profile is usually characterized by a power law of the form n(r) ∝ r, with a slope that is steeper than that of a flat isothermal → core. For a single-mass stellar cluster, Bahcall & Wolf (1976) determined the dynamically relaxed cusp will have γ = 7/4. The presence of such a cusp is important observationally because it may represent a simple test for black holes in stellar systems where dynamical mass estimates are difficult, such as in the cores of galaxies. In the case of the Milky Way, several attempts have been done to probe the presence of such a stellar cusp. However, the presence of the cusp is not confirmed. For example, based on the late-type stars alone, Do et al. (2009, ApJ 703, 1323), show that γ is less than 1.0 at the 99.7% confidence level. This is consistent with the nuclear star cluster having no cusp, with a → core profile that is significantly flatter than that predicted by most cusp formation theories, and even allows for the presence of a central hole in the stellar distribution (See also Genzel et al., 2010, Rev.Mod.Phys. 82, 3121, also at astro-ph/1006.0064).

stellar; → cusp.

stellar dynamics
  توانیک ِ ستاره‌ای   
tavânik-e setâre-yi

Fr.: dynamique stellaire   

The field of astrophysics that describes systems of many → point mass particles whose mutual gravitational interactions determine their orbits. Theses systems include → star clusters, → globular clusters, and galaxies (→ galaxy) consisting of about 102-103, 104-106, and up to about 1012 members respectively. Stellar dynamics deals with systems in which each member contributes importantly to the overall gravitational field and is usually concerned with the statistical properties of many orbits. It can be compared to the → kinetic theory of gases developed in the late 19th century. In contrast, → celestial mechanics deals with systems where the gravitational force of a massive planet or star determines the orbits of its satellites.

stellar; → dynamics.

stellar evolution
  فرگشت ِ ستاره   
fargašt-e setâré

Fr.: évolution stellaire   

The gradual changes in physical state (spectrum, luminosity, temperature) and chemical composition that occurs during the life of a star.

stellar; → evolution.

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