An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 48 Search : formation
affine transformation
  ترادیس ِ کروَن   
tarâdis-e karvan

Fr.: transformation affine   

Any → transformation preserving → collinearity.

affine; → transformation.

biased galaxy formation
  دیسش ِ ورکدار ِ کهکشانها   
diseš-e varakdâr-e kahkašânhâ

Fr.: formation biaisée de galaxies   

The theory that bright galaxies form preferentially from anomalously overdense perturbations in the → early Universe.

biased; → galaxy; → formation.

bimodal star formation
  دیسش ِ دومد ِ ستارگان   
diseš-e domod-e setâregân

Fr.: formation bimodale d'étoile   

A concept of → star formation in which → high-mass stars and → low-mass stars form in different physical conditions involving different → molecular clouds. Following the pioneering suggestion of Herbig (1962), successive investigations have generally supported the idea that star formation proceeds bimodally with respect to stellar mass. The star formation rate appears to differ both spatially and temporally for low mass and → massive stars. This is of considerable importance for galactic evolution, since the low-mass stars lock up mass and are long-lived, low luminosity survivors to the present epoch, whereas massive stars are short-lived, recycle and enrich interstellar gas, and leave dark remnants while producing a high luminosity per unit of mass (Silk, J., 1988, in Galactic and Extragalactic Star Formation, p. 503, eds. R. E. Pudritz and M. Fich).

bimodal; → star; → formation.

bottom-up structure formation
  دیسش ِ ساختار از پایین به بالا   
diseš-e sâxtâr az pâyin bé bâlâ

Fr.: formation des structures du bas vers le haut   

A → structure formation scenario in which small galaxies form first, and larger structures are then formed in due course. Contrary to → top-down structure formation.

bottom; → up; → structure; → formation; → galaxy.

burst of star formation
     
belk-e diseš-e setâregân

Fr.: flambée de formation d'étoiles   

An intense → star formation activity in a region of → interstellar medium or, more globally, in a → galaxy. It is characterized by a → star formation rate which is much higher than the corresponding average. Same as → starburst.

burst; → star; → formation.

CO formation
  دیسش ِ CO   
diseš-e CO

Fr.: formation de CO   

The chemical reaction that gives rise to → carbon monoxide in the → interstellar medium. According to models, several processes may lead to CO formation. For example, HCO+ + e → CO + H. The molecule HCO+ is itself produced through several paths, for example: H3+ + C → CH2+ + H, CH2+ + H2 → CH3+ + H, CH3+ + O → HCO+ + H. Alternatively: C+ + H2O → HCO+ + H. Another possibility: C+ + OH → CO+ + H, CO+ + H2→ HCO+ + H.

carbon monoxide; → formation.

collective star formation
  دیسش ِ گرد‌آمدی ِ ستارگان   
diseš-e gerdâmdi-ye setâregân

Fr.: formation collective d'étolies   

Formation of stars, especially → massive stars, in group as opposed to individual formation.

collective; → star; → formation.

color transformation
  ترادیس ِ رنگ   
tarâdis-e rang

Fr.: transformation de couleur   

Empirical mathematical transformation applied to the observed magnitudes in order to convert them into a standard system, or into a different system.

color; → transformation.

cosmic star formation peak
  چکاد ِ کیهانی ِ دیسش ِ ستارگان   
cakâd-e keyhâni-ye diseš-e setâregân

Fr.: pic de formation stellaire cosmique   

A crucial period in the history of the → Universe, when the bulk of stars in massive galaxies were likely formed. Observations of young stars in distant galaxies at different times in the past have indicated that the → star formation rate peaked at the → redshift of z ~ 2, some 10 billion years ago, before declining by a factor of around ten to its present value (P. Madau & Dickinson, 2014, arXiv:1403.0007).

cosmic; → star; → formation; → peak.

deformation
  وادیس، وادیسش، وادیسانش   
vâdis, vâdiseš, vâdisâneš

Fr.: déformation   

Altering in the size or shape of a body. See also → deformable.

Verbal noun of → deform.

elastic deformation
  وادیسش ِ کشایند   
vâdiseš-e kešâyand

Fr.: déformation élastique   

A deformation of a → solid body in which the change (→ strain) in the relative position of points in the body disappears when the deforming stress is removed. See also → elastic limit.

elastic; → deformation.

formation
  دیسش   
diseš

Fr.: formation   

1) The act or process of forming or the state of being formed, such as → star formation.
2) Geology: A laterally continuous rock unit with a distinctive set of characteristics that make it possible to recognize and map from one → outcrop or well to another. The basic rock unit of stratigraphy.

Verbal noun of → form, + -ate + -ion.

Diseš, verbal noun of disidan, → from dis-, → form, + -eš.

galaxy formation
  دیسش ِ کهکشان   
diseš-e kahkešân

Fr.: formation de galaxies   

The study dealing with the processes that gave rise to galaxies in a remarkably → early Universe. See also → structure formation, → protogalaxy

galaxy; → formation.

Galilean transformation
  ترادیس ِ گالیله‌ای   
tarâdis-e Gâlile-yi (#)

Fr.: transformation galiléenne   

The method of relating a measurement in one → reference frame to another moving with a constant velocity with respect to the first within the → Newtonian mechanics. The Galilean transformation between the coordinate systems (x,y,z,t) and (x',y',z',t') is expressed by the relations: x' = x - vt, y' = y, z' = z. Galilean transformations break down at high velocities and for electromagnetic phenomena and is superseded by the → Lorentz transformations.

Galilean, of or pertaining to Galileo Galilei (1564-1642), Italian physicist and astronomer; → transformation.

gauge transformation
  ترادیس ِ گز   
tarâdis-e gaz (#)

Fr.: transformation de jauge   

A change of the fields of a gauge theory that does not change the value of any measurable quantity.

gauge; → transformation.

grain formation
  دیسش ِ دانه   
diseš-e dâné

Fr.: formation des grains   

The process by which dust grains are assembled or produced.

grain; → formation.

hierarchical structure formation
  دیسش ِ ساختار ِ پایگانی   
diseš-e sâxtâr-e pâygâni

Fr.: formation de structures hiérarchiques   

A cosmological → structure formation model in which the smallest gravitationally bound structures (→ quasars and galaxies) form first, followed by → groups, → galaxy clusters, and → superclusters of galaxies.

hierarchical; → structure; → formation.

image formation
  دیسش ِ تصویر   
diseš-e tasvir

Fr.: formation de l'image   

The meeting of light rays emanating from an object after crossing an optical system.

image; → formation.

information
  ازدایش   
azdâyeš (#)

Fr.: information   

1) Knowledge gained through study, communication, research, instruction, etc.
2) Knowledge communicated or received concerning a particular fact or circumstance; news.
3) The act or fact of informing.
4) A sequence of signals that conveys a message to a receiver. Information does not exist on its own. It is contained within something and is coded. The notion of information involves → uncertainty and → randomness; hence the necessity for calling on → probability theory and → statistics.
See also: → information content, → information entropy, → information flow, → information paradox, → information science, → information technology, → information theory, → infosphere, → quantum information, → entropy.

Verbal noun of → inform.

information content
  پربنه‌ی ِ ازدایش   
parbane-ye azdâyeš

Fr.: contenu d'information   

The → negative of the → logarithm of the → probability that a particular → message or → symbol will be emitted by a → source.

information; → content.

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