An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 1333
stellar magnetic field
  میدان ِ مغناتیسی ِ ستاره‌ای   
meydân-e meqnâtisi-ye setâre-yi

Fr.: champ magnétique stellaire   

The → magnetic field associated with a star. Magnetic fields are common among stars of solar and lower masses. So far definitive detections of fields in stars with masses ~1.5 Msun have, for the most part, been made for objects having anomalous chemical abundances (e.g., the → chemically peculiar A and B stars). Recently, however, observations of cyclic variability in the properties of → stellar winds from luminous → OB stars have been interpreted as evidence for the presence of large-scale magnetic fields in the surface layers and atmospheres of these objects (→ magnetic massive star). These inferences have been bolstered by the unambiguous measurement of a weak (~ 360 G) field in the chemically normal B1 IIIe star → Beta Cephei. These results suggest that magnetic fields of moderate strength might be more prevalent among → hot stars than had previously been thought. At the present time, the origin of magnetism in massive stars is not well understood. If the magnetic field of a hot star is produced by → dynamo effect in the → convective core, then a mechanism for transporting the field to the stellar surface must be identified. The finite electrical conductivity of the envelope leads to the outward diffusion of any fields contained therein, but only over an extended period of time. Estimates indicate that for stars more massive than a few solar masses, the resistive diffusion time across the radiative interior exceeds the → main sequence lifetime. Another possibility is that dynamo fields are advected from the core to the surface by rotation-induced → meridional circulation (MacGregor & Cassinelli, 2002, astro-ph/0212224).

stellar; → magnetic; → field.

stellar nucleosynthesis
  هسته‌هندایش ِ ستاره‌ای   
haste-handâyeš-e setâre-yi

Fr.: nucléosynthèse stellaire   

The → nuclear reaction process taking place inside stars, whereby → chemical elements are produced from pre-existing nuclei heavier than → hydrogen and → helium.

stellar; → nucleosynthesis.

stellar object
  بر‌آخت ِ ستاره‌ای   
barâxt-e setâre-yi

Fr.: objet stellaire   

Any of a class of → astronomical objects which is thought to evolve into a → star or is a descendant of a star.

stellar; → object.

stellar parallax
  دیدگشت ِ ستاره   
didgašt-e setâré

Fr.: parallaxe stellaire   

The apparent → difference in the → position of a → celestial object as seen by an → observer from two widely separated → locations. The parallax of an object can be used to derive its → distance. The relationship between the → parallax angle  p (measured in seconds of arc) and the distance d (measured in → astronomical units) is given by d = 206,264 / p. For a parallax angle p = 1'', the distance to the star would correspond to 206,264 AU. By convention, the distance unit → parsec is defined to be equivalent to 206,264 AU. Therefore, the parallax relation takes the much simpler form: d (in pc) = 1/p (in seconds of arc). The first star whose parallax was measured was → 61 Cygni (Bessel, 1838).
See also:
annual parallax, → diurnal parallax, → dynamical parallax, → geocentric parallax, → heliocentric parallax, → horizontal parallax, → lunar parallax, → mean parallax, → parallactic ellipse, → parsec, → photometric parallax, → secular parallax, → solar parallax, → spectroscopic parallax, → statistical parallax, → trigonometric parallax.

stellar; → parallax.

stellar photometry
  نورسنجی ِ ستاره‌ای   
nursanji-ye setâre-yi

Fr.: photométrie stellaire   

The precise measurement of a star's brightness, usually through several specific wavelength bands.

stellar; → photometry.

stellar physics
  فیزیک ِ ستاره‌ای   
fizik-e setâre-yi (#)

Fr.: physique stellaire   

Same as → stellar astrophysics.

stellar; → physics.

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
  ساختار ِ ستاره، ~ ستاره‌ای   
sâxtâr-e setâré, ~ setêre-yi

Fr.: structure stellaire   

A physical model that describes the internal arrangement of a star in detail and makes detailed predictions about the luminosity, the color, and the future evolution of the star.

stellar; → structure.

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.

stellar wind
  باد ِ ستاره‌ای   
bâd-e setâre-yi

Fr.: vent stellaire   

The steady flow of gas away from a star resulting in → mass loss. They range from gentle solar wind (2 x 10-14 solar masses per year) to violent winds some 10 billions times stronger (10-4 solar masses per year) for hot, massive stars.

stellar; → wind.

stellar-mass black hole
  سیه‌چال با جرم ِ ستاره‌ای   
siyah câl bâ jerm-e setâre-y

Fr.: trou noir de masse stellaire   

Same as → stellar black hole.

stellar; → mass; → black; → hole.

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.

Stephan's Quintet
  پنج‌تایه‌ی ِ استفان   
panjtâye-ye Stephan

Fr.: Quintet de Stéphan   

A group of five closely grouped galaxies (NGC 7317, 7318A, 7318B, 7319 and 7320) in the constellation → Pegasus. Four of the galaxies show essentially the same → redshift, suggesting that they are at the same distance from us. The fifth galaxy (NGC 7320) has a smaller redshift than the others, indicating it is much closer. This one is probably a foreground galaxy which happens to lie along the line of sight. The four distant galaxies seem to be colliding, showing serious distortions due to gravitational → tidal forces. The NASA → Spitzer Space Telescope has revealed the presence of a huge intergalactic → shock wave. Collisions play an important role in the life cycles of galaxies. → merging galaxies.

Named after the French astronomer Edouard Stéphan (1837-1923), who discovered the group in 1877 at Marseilles Observatory, using the → Foucault's reflector; → quintet.

steradian (sr)
  استرادیان   
esterâdiân (#)

Fr.: stéradian   

The solid angle subtended at the center of a sphere by an area on its surface numerically equal to the square of the radius. → square degree.

From ste(reo)-, → stereo- + → radian.

stere-, stereo-
  استریو-   
estereyo- (#)

Fr.: stéréo-   

A combining form meaning "having and dealing with three dimensions of space; solid."

From stereo a shortening of stereotype, from Fr. stéréotype (adj.) "printing by means of a solid plate of type," from Gk. stereos "solid."

Loan from Fr., as above.

stereo-comparator
  هم‌سنج‌گر ِ استریو   
ham-sanj-gar-e estereyo

Fr.: stéréo comparateur   

A device that allows two images of the sky taken at different times to be optically superimposed so that changes in star brightness or moving objects can be detected.

stereo-; comparator, from L. comparare "to place together, match," from compar "alike, matching," → com-; → partial + -tor.

Ham-sanj-gar "comapartor," from ham-, → com-, + sanj stem of sanjidan "to compare" + -gar, → -or; → stereo-.

stereographic
  استریونگاری، استریونگاریک   
estereyonegâri, estereyonegârik

Fr.: stétéographique   

Of, relating to, or being a delineation of the form of a solid body on a plane.

stereography; → -ic

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