An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 3079 Search : on
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 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.

stellar population
  پُرینش ِ ستاره‌ای   
porineš-e setâre-yi

Fr.: population stellaire   

Population I star; → Population II star.

stellar; → population.

stellar population synthesis
  هندایش ِ پرینش‌های ِ ستاره‌ای   
handâyeš-e porinešhâ-ye setâre-yi

Fr.: synthèse de poupulations stellaires   

A theoretical model that reconstructs the integrated spectrum of → stellar populations from an empirical library of stellar spectra containing the range of types expected to be present in the sample. The light received from a given galaxy is emitted by a large number of stars that may have different masses, ages, and metallicities. Stellar population synthesis models are tools for interpreting the integrated light that we observe from the galaxies.

stellar; → population; → model.

stellar pulsation
  تپش ِ ستاره، ~ ستاره‌ای   
tapeš-e setâré, ~ setâre-yi

Fr.: pulsation stellaire   

The expansion of a star followed by contraction so that its → surface temperature and → luminosity undergo periodic variation. Pulsation starts with a loss of → hydrostatic equilibrium, when, for example, a layer contracts. This layer heats up and becomes more opaque to radiation. Therefore, radiative diffusion slows down through the layer because of its increased → opacity and heat increases beneath it. Hence pressure rises below the layer. Eventually this increase in pressure starts to push the layer out. The layer expands, cools and becomes more transparent to radiation. Energy now escapes from below the layer and the pressure beneath the layer drops. The layer falls inward and the cycle starts over. See also → kappa mechanism; → gamma mechanism; → partial ionization zone; → pulsating star; → valve mechanism.

stellar; → pulsation.

stellar rotation
  چرخش ِ ستاره، ~ ستاره‌ای   
carxeš-e setâré, é setêre-yi

Fr.: rotation stellaire   

The spinning of a star about its axis, due to its angular momentum. Stars do not necessarily rotate as solid bodies, and their angular momentum may be distributed non-uniformly, depending on radius or latitude.Thus the equator of the star can rotate at a different angular velocity than the higher latitudes. These differences in the rate of rotation within a star may have a significant role in the generation of a stellar magnetic field.

stellar; → rotation.

stellar structure equation
  هموگش ِ ساختار ِ ستاره   
hamugeš-e sâxtâr-e setâré

Fr.: équation de structure stellaire   

A set of → differential equations describing the physical properties of stars based on two main assumptions: a star is a perfect sphere and the net force on a macroscopic mass element is zero. If the effects of rotation and magnetism are ignored, these assumptions lead to a set of five differential equations.

stellar; → structure; → equation.

step function
  کریای ِ پله‌ای   
karyâ-ye pelle-yi

Fr.: fonction échelon   

Math.: A function f of a real variable defined on an interval [a,b] so that [a,b] can be divided into a finite number of sub-intervals on each of which f is a constant. The graph of a step function is a series of line segments resembling a set of steps.

Step, from M.E. steppen, O.E. steppan; cf. Du. stap, O.H.G. stapfo, Ger. stapfe "footprint;" → function.

Karyâ, → function; pellé "stair, step;" Mid.Pers. pylg "step," pillagân "steps, staircase;" from *palak, from *padak, from pad-, → foot, + relation suffix -ak.

stereographic projection
  فراشانش ِ استریونگاریک   
farâšâneš-e estereyonegârik

Fr.: projection stéréographique   

A graphical method of depicting three-dimensional geometrical objects in two dimensions. In a → planispheric astrolabe, it is the projection of a point of the celestial sphere onto the equatorial plane, as seen from one of the poles. The center of projection is the South pole for the northern hemisphere, and the North pole for the southern hemisphere. In this operation the projection of any circle of the sphere remains a circle on the projection plane and moreover the projection does not alter angles.

stereographic; → projection

stimulated emission
  گسیل ِ گوازیده   
gosil-e gavâzidé

Fr.: émission stimulée   

The process by which an electron, which is already in an excited state (an upper energy level, in contrast to its lowest possible level or "ground state"), can "stimulate" a transition to a lower level, producing a second photon of the same energy. The quantum energy of the incoming photon should be equal to the energy difference between its present level and the lower level. This process forms the basis of both the → laser and → maser. Same as → induced emission.

Stimulated, p.p. of → stimulate; → emission.

stimulated star formation
  دیسش ِ گوالیده‌ی ِ ستاره   
diseš-e gavâlide-ye setâré

Fr.: formation stimulée d'étoiles   

A process in which a star is not formed spontaneously but is provoked by the action of external forces, such as pressure and shock on a molecular cloud by close-by → massive stars, → supernova explosions, etc. See also → sequential star formation.

Stimulated, p.p. of → stimulate; → star formation.

Stirling's approximation
  نزدینش ِ استرلینگ   
nazdineš-e Stirling

Fr.: approximation de Stirling   

A mathematical formula yielding an approximate value for → factorial n, when n is large: n! ≅ (2πn)1/2nne-n, where e is the base of → natural logarithm.

Named after James Stirling (1692-1770), a Scottish mathematician; → approximation.

stochastic excitation
  بر‌انگیزش ِ کاتورگین   
barangizeš-e kâturgin

Fr.: excitation stochastique   

The mechanism arising from turbulent convection in the → convective zone of stars, which is responsible for the driving of stellar → pulsation modes. In stars cooler than typically ~ 7 500 K (→ F-type stars and cooler), the stochastic excitation occurs in the convection envelope. In massive stars, it may develop either in the → convective core or in the convective layer beneath the → photosphere. Recent studies suggest that in → Be stars stochastic excitation takes place in the convective core. The stochastic waves can transport → angular momentum from the core to the surface. Fast rotation, as in Be stars, amplifies the stochastic excitation.

stochastic; → mode.

stochastic self-propagating star formation
  دیسش ِ ستارگان با خود-توچش ِ کاتورگین   
diseš-e setâregân bâ xod-tuceš-e kâturgin

Fr.: formation d'étoiles par auto-propagation stochastique   

A mechanism that could be responsible for global → spiral structure in galaxies either by itself or in conjunction with spiral → density waves. In this mechanism, star formation is caused by → supernova-induced → shocks which compress the → interstellar medium. The → massive stars thus formed may, when they explode, induce further → star formation. If conditions are right, the process becomes self-propagating, resulting in agglomerations of young stars and hot gas which are stretched into spiral shaped features by → differential rotation. Merging of small agglomerations into larger ones may then produce large-scale spiral structure over the entire galaxy. The SSPSF model, first suggested by Mueller & Arnett (1976) was developed by Gerola & Seiden (1978). While the → density wave theory postulates that spiral structure is due to a global property of the galaxy, the SSPSF model examines the alternative viewpoint, namely that spiral structure may be induced by more local processes. The two mechanisms are not necessarily mutually exclusive, but they involve very different approaches to the modeling of galaxy evolution. The SSPSF gives a better fit than the density wave theory to the patchy spiral arms found in many spiral galaxies. However, it cannot explain → galactic bars.

stochastic; → self; → propagate; → star; → formation.

Stokes friction factor
  کروند ِ مالش ِ استوکس   
karvand-e mâleš-e Stokes

Fr.: facteur de friction de Stokes   

For the translational motion of a spherical body moving in a → viscous fluid, the proportionality factor between the uniform flow velocity far from the sphere and the drag force, provided no-slip boundary condition and small → Reynolds numbers: f = 6πηR, where η is the Reynolds number and R radius of the sphere.

Stokes; → friction; → factor.

sang (#)

Fr.: pierre   

The hard nonmetallic mineral or group of consolidated minerals either in mass or in a fragment of pebble or larger size. See also → rock.

O.E. stan; cf. O.N. steinn, Dan. steen, O.H.G., Ger. Stein; from PIE *stai- "stone," also "to thicken, stiffen" (cf. Skt. styayate "curdles, becomes hard;" Av. stay- "heap;" Gk. stear "fat, tallow," stia, stion "pebble").

Sang "stone, rock;" Mid.Pers. sang; O.Pers. aθanga-; Av. asenga- "stone;" PIE *aken-.

Stone Age
  عصر ِ سنگ   
asr-e sang (#)

Fr.: âge du fer   

A prehistoric period during which the main material used to make tools and weapons was stone. The Stone Age is usually divided into three separate periods (Paleolithic Period, Mesolithic Period, and Neolithic Period) based on the degree of sophistication in the fashioning and use of tools. The Paleolithic time period is by far the longest, beginning some two million years ago and ending around 10,000 BC to coincide with the end of the last ice age (Pleistocene epoch).

stone; → age.

stony meteorite
  شخانه‌ی ِ سنگی   
šaxân-ye sangi

Fr.: météorite pierreuse   

A meteorite composed largely of rock-forming (→ silicate) → minerals. Stony meteorites are the most abundant kind, about 95%, of all meteorites. They are divided into two groups: → chondrites and → achondrites.

stone; → meteorite.

stony-iron meteorite
  شخانه‌ی ِ سنگی-آهنی   
šaxâne-ye sangi-âhani

Fr.: sidérolithe, sidérolite   

Meteorites comprised of roughly equal amounts of → nickel/→ iron and → stone. They are divided into two groups: → pallasites and → mesosiderites. The stony-irons are thought to have formed at the core/mantle boundary of their parent bodies. The stony-irons account for less than 2% of all known meteorites. Also called → siderolite.

stony; → iron; → meteorite.

stop consonant
  هم‌آوای ِ ایستی   
hamâvâ-ye isti

Fr.: consonne occulsive   

occlusive consonant.

stop; → consonant.

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