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: 1251
Class 0
  رده‌ی ِ 0   
rade-ye 0

Fr.: Classe 0   

A low-mass → protostar deeply embedded in a → circumstellar dusty envelope and resulting from the → gravitational collapse of a dense → pre-stellar core. This stage in the process of star formation occurs typically a few 104 years after the onset of the collapse. Class 0 protostars represent the earliest stage of → young stellar objects. The → spectral energy distribution (SED) of a Class 0 object resembles a → blackbody spectrum at a temperature below ~ 15-30 K, peaking at → submillimeter wavelengths beyond 100 μm. The central protostar has not yet acquired its final mass, since → accretion is still going on, and the envelope (detected in submillimeter wavelengths) is more massive than the central protostellar mass. Moreover, these objects show powerful → bipolar ejections of material in the form of collimated → carbon monoxide (CO)outflows which distinguish them from the pre-stellar phase of star formation. The subsequent evolution of a Class 0 is a → Class I.

class; → zero.

Class I
  رده‌ی ِ I   
rade-ye I

Fr.: Classe I   

A protostellar phase resulting from the evolution of a → Class 0 object typically a few 105 years after the beginning of the → gravitational collapse. The protostar grows in mass due to → accretion from the envelope, which becomes less massive than the protostar. An → accretion disk forms around the protostar through which mass is transferred to the central object. The → spectral energy distribution (SED) changes with respect to that of a Class 0. The peak of the SED shifts to → far infrared wavelengths (below 100 μm) as the temperature of the dust rises. Emission from both the envelope (about 100 K) and the thick disk (a few 100 K) are observed. The SED has a positive → spectral index (αIR > 0), so that the bulk of the → luminosity (still due to accretion) emerges at the longer infrared wavelengths. Moreover, → bipolar outflows and → jets are observed which are generally less powerful than those in Class 0 objects. Class I objects evolve into → Class II.

class; → one.

Class II
  رده‌ی ِ II   
rade-ye II

Fr.: Classe II   

A stage in the evolution of low-mass → protostars resulting from a → Class I object about 106 years after the initial → gravitational collapse. Most of the envelope has been removed and the embedded object becomes visible at infrared and optical wavelengths. At this stage, the bulk of the material has → accreted onto the central object. A flattened → circumstellar disk or → protoplanetary disk is present in which material moves inward at a decreasing rate. The disk contributes only about 1% of the total mass of the system. Material from a remaining envelope may still accrete onto the outer parts of the disk. The → spectral energy distribution (SED) at → near infrared wavelengths is dominated by the emission of the central protostar and typically peaks around 2 μm, corresponding to temperatures around 1000 to 2000 K. At longer wavelengths an → infrared excess is observed, originating from the disk. The SED has a negative → spectral index (-1.5 < αIR < 0). Estimated disk masses and → accretion rates are 10-3 to 10-1 → solar masses and 10-8 solar masses per year, respectively. This stage initiates the → pre-main sequence stage of a star. The object is referred to as a → classical T Tauri star. The stellar → photosphere is revealed at optical wavelengths accompanied by strong → emission lines and photometric variability, but the infrared luminosity is far larger than can be explained by the photometric temperature and radius.

class; → two.

Class III
  رده‌ی ِ III   
rade-ye III

Fr.: Classe III   

An evolutionary stage in the formation of low-mass → protostars resulting from a → Class II object between 1 to 10 million years after the initial → gravitational collapse. At this stage → accretion has ceased completely and what remains from the → circumstellar disk is a → debris disk. The temperature and density of the → pre-main sequence star keep increasing as the object slowly contracts to its final size. Most of the → luminosity derives from protostellar contraction. The → spectral energy distribution (SED) resembles a stellar → blackbody, peaking at optical and infrared wavelengths. Minor → infrared excess is still observed. The SED has a negative → spectral index (αIR < -1.5). Class III objects are sometimes called → weak-line T Tauri stars.

class; → three.

classical
  کلاسیک   
kelâsik (#)

Fr.: classique   

1) Considered as the typical, traditional, or usual form of something. → classical T Tauri star.
2) → classical physics.

From classic (+ → -al), from Fr. classique, from L. classicus "belonging to a class, relating to the first or highest class of the Roman people," from classis perhaps akin to calare "to call."

Loan from Fr. classique, as above.

classical bulge
  کوژ ِ کلاسیک   
kuž-e kelâsik

Fr.: bulbe classique   

A → galaxy bulge that appears protruding from the disk plane when seen at an appropriate → inclination. Classical bulges are somewhat → spheroidal, featureless (no → spiral arms, → bars, → rings, etc.), contain mostly → old stars (not much dust or star-forming regions), and are kinematically hot, i.e. dynamically supported by the → velocity dispersion of their stars. Their → surface brightness profile follows the → de Vaucouleurs law. Currently, they are thought to form through → gravitational collapse or → mergers in violent events, inducing a fast → burst of star formation if gas is available. An example is the → Sombrero galaxy bulge (D. A. Gadotti, 2012, astro-ph/1208.2295).

classical; → bulge.

classical field theory
  نگره‌ی ِ کلاسیک ِ میدان   
negare-ye klâsik-e meydân

Fr.: théorie classique des champs   

The theory that studies distributions of → energy, → matter, and other physical quantities under circumstances where their discrete nature is unimportant. Classical field theory traditionally includes → Newtonian mechanics, Maxwell's → electromagnetic theory, and Einstein's theory of → general relativity. The main scope of classical field theory is to construct the mathematical description of → dynamical systems with an infinite number of degrees of freedom. The word "classical" is used in contrast to those field theories that incorporate → quantum mechanics (→ quantum field theory). Classical field theories are usually categorized as → non-relativistic and → relativistic.

classical; → field; → theory.

classical logic
  گوییک ِ کلاسیک   
guyik-e kelâsik

Fr.: logique classique   

The traditional logic in which → sets are sharply defined (→ crisp set) for example, the number of students registered for a course, or the names beginning with P in a given telephone directory. Classical logic also defines relations between sets of → propositions. Consider for example two sets: elephants and mammals, a simple proposition would be the assertion that all elephants are mammals, that is E ⊂ M, where E is the elephant set and M is the mammal set. The classical logic proposition is either true or false. Compare with → fuzzy logic.

classical; → logic.

classical mechanics
  مکانیک کلاسیک   
mekânik kelâsik (#)

Fr.: mécanique classique   

The branch of physical science which deals with the motions of bodies travelling at velocities that are very much less than that of light in a vacuum. Same as → Newtonian mechanics.

classical; → mechanics.

classical physics
  فیزیک ِ کلاسیک   
fizik-e kelâsik (#)

Fr.: physique classique   

Physics not taking into account → quantum mechanics or Einstein's → relativity theory. Classical physics includes the branches developed before the beginning of the 20th cantury: Mechanics, Acoustics, Optics, Thermodynamics, and Electricity and Magnetism. Most of classical physics is concerned with matter and energy on the normal scale of observation.

classical; → physics.

classical T Tauri star
  ستاره‌ی ِ T-گاو ِ کلاسیک   
setâre-ye T-Gâv-e kelâsik

Fr.: étoile T Tauri classique   

A → T Tauri star in which → accretion from a → circumstellar disk is responsible for ultraviolet and infrared excess emission and for a moderate to strong emission line spectrum superimposed on the photospheric spectrum. Classical T Tauri stars probably evolve into → weak-line T Tauri stars when their disks are fully accreted by the stars.

classical; → T Tauri star.

classification
  رده بندی   
radebandi (#)

Fr.: classification   

The systematic grouping of astronomical objects into categories on the basis of physical, morphological, or evolutionary characteristics.

Classification, from O.Fr., from classifier, from → class + -fier, from L. -ficare, root of facere "to make, do;" PIE base *dhe- "to put, to do" (cf. Skt. dadhati "puts, places;" Av. dadaiti "he puts," O.Pers. ada "he made," Gk. tithenai "to put, set, place."

Radebandi, from radé, → class, + bandi, verbal noun of bastan "to bind, shut; to get, acquire, incur," from Mid.Pers. bastan/vastan "to bind, shut;" Av./O.Pers. band- "to bind, fetter," banda- "band, tie;" cf. Skt. bandh- "to bind, tie, fasten;" Ger. binden, E. bind, → band; PIE base *bhendh- "to bind."

clathrate
  کلاترات   
klâtrât

Fr.: clathrate   

A chemical substance in which a molecule of one compound fills a cavity within the crystal lattice of another compound. An example is clathrate hydrate, a special type of gas hydrate in which small molecules (typically gases) are trapped inside "cages" of hydrogen bonded water molecules. Large amounts of methane have been discovered both in permafrost formations and under the ocean floor. Similarly oceans contain large quantities of trapped CO2, which dissociate when the temperature rises sufficiently.

From L. clathratus, p.p. of clathrarer "to fit with bars," from clathra "bars, lattice," from Gk. kleithron " bar," from kleiein "to close."

clause
  بند   
band (#)

Fr.: clause   

1) Grammar: A syntactic construction containing a subject and predicate and forming part of a sentence or constituting a whole simple sentence.
2) A distinct article or provision in a contract, treaty, will, or other formal or legal written document (Dictionary.com).

M.E., from O.Fr. clause, from M.L. clausa "conclusion," used in the sense of classical L. clausula "the end, a closing, termination," also "end of a sentence or a legal argument," from clausa, from p.p. of claudere "to close, to shut, to conclude," → closure.

Band present stem of bastan "to close, to fasten, to bind," → closure.

Clausius equation
  هموگش ِ کلاؤزیوس   
hamugeš-e Clausius

Fr.: équation de Clausius   

A first-order improvement on the → ideal gas law that corrects for the finite volume of molecules.

After Rudolf Clausius (1822-1888), a German physicist and mathematician, → equation.

Clausius's postulate
  فراوس ِ کلاؤزیوس   
farâvas-e Clausius

Fr.: postulat de Clausius   

If heat flows by conduction from body A to another body B, then a transformation whose only final result is to transfer heat from B to A is impossible. Clausius's postulate is a formulation of the → second law of thermodynamics. It is also equivalent to → Kelvin's postulate.

Clausius equation; → postulate.

Clausius-Clapeyron equation
  هموگش ِ کلاؤزیوس-کلاپرون   
hamugeš-e Clausius-Clapeyron

Fr.: équation de Clausius-Clapeyron   

An approximation of the → Clapeyron equation for liquid-vapor equilibrium that incorporates the → ideal gas law and states that the logarithm of vapor pressure is inversely proportional to temperature.

Clausius equation; → Clapeyron equation.

clay
  رُس   
ros (#)

Fr.: argile   

A broad class of hydrous → silicate minerals that has the tetrahedral silicate groups linked in sheets. Clay commonly forms as a product of rock weathering. Deposits of phyllosilicates, such as chamosite and nontronite, recently identified on Mars are attributed to the action of liquid water in the past history of this planet.

O.E. clæg "stiff, sticky earth; clay," from PIE base *glei- "to stick together;" cf. Gk. gloios "sticky substance," L. glus, gluten "glue," O.Slav. glina "clay." The Pers. gel "clay, mud," Mid.Pers. gil "clay" may belong to this family.

Ros, variant rost "clay," of unknown origin.

clear
  رونه   
runé (#)

Fr.: clair   

1) Free from darkness, obscurity, or cloudiness.
2) Transparent; pellucid.
3) Without discoloration, defect, or blemish (Dictionary.com). → clear night.

M.E. clere, from O.Fr. cler, from L. clarus "clear, bright, distinct."

Runé, from Kurd. (Sorani) rûn "bright, clear," rûn kirdin "to explain," variant of rowšan, → bright.

clear night
  شب ِ رونه   
šab-e runé

Fr.: nuit claire   

A night sky without clouds, mist, or haze, atmospheric dust particles, and without city lights in which a sixth magnitude star is visible by naked-eye.

clear; → night.

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