An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 471 Search : ity
spectral density
  چگالی ِ بینابی   
cagâli-ye binâbi

Fr.: densité spectrale   

For a specified → bandwidth of radiation consisting of a continuous → frequency spectrum, the total → power in the bandwidth divided by the bandwidth. Spectral density describes how the power (or variance) of a time series is distributed with frequency. Also called power spectral density.

spectral; → density.

spectral variability
  ورتندگی ِ بینابی   
vartandegi-ye binâbi

Fr.: variabilité spectrale   

The state of a spectrum from an astronomical object in which the lines change with time as far as their intensity, profile, and wavelength are concerned.

spectral; → variability.


Fr.: spiritualité   

The quality or fact of being → spiritual.

spiritual; → -ity..

pâydâri (#)

Fr.: stabilité   

A condition in which a dynamical system slightly displaced from its equilibrium configuration always tends to return to this configuration. → instability, → instability strip.

Noun from adj. → stable.

stellar luminosity
  تابندگی ِ ستاره   
tâbandegi-ye setâré

Fr.: luminosité stellaire   

The total amount of energy emitted by a star per unit time. According to the → Stefan-Boltzmann law, the stellar luminosity is given by: L* = 4πR*2σTeff4, where R* is radius, σ is the → Stefan-Boltzmann constant, and Teff is → effective temperature. A star's luminosity depends, therefore, on two factors, its size and its surface temperature. Stellar luminosity is measured either in ergs per second or in units of → solar luminosity or in → absolute magnitude. See also → luminosity class.

stellar; → luminosity.

stellar metallicity
  فلزیگی ِ ستاره‌ای   
felezigi-ye setâre-yi

Fr.: métallicité stellaire   

The metallicity derived from observations of stars in galaxies. It is mainly based on spectral → absorption lines in → ultraviolet (UV) and optical ranges. Stellar metallicity is a direct measure of the amount of metals in a galaxy, since large part of heavy elements lies in its stars.

stellar; → metallicity.


Fr.: subjectivité   

1) The state or quality of being → subjective. Contrasted with → objectivity.
2) The interpretation based on individual personal feelings and opinions rather than on external → facts.

subjective + → -ity.


Fr.: nature sous-stellaire   

The fact or condition, for an object, of not being capable to sustain the → hydrogen fusion because of its low mass (less than 0.08 → solar masses).

substellar + → -ity.


Fr.: superconductivité   

The phenomenon in which certain materials, when cooled to a sufficiently low temperature, lose all resistance to the flow of electricity.

super-; → conductivity


Fr.: superfluidité   

The phenomenon occurring in → liquid helium (→ helium I) cooled below the → lambda point temperature of 2.17 K, whereby it flows freely with no measurable → friction and → viscosity.

super-; → fluidity.

surface density
  چگالی ِ رویه‌ای   
cagâli-ye ruye-yi

Fr.: densité de surface   

The amount of a quantity distributed over a surface area divided by the area, such as a surface-charge density.

surface; → density.

surface gravity
  گرانی ِ رویه، ~ رویه‌ای   
gerâni-ye ruyé, ~ ruye-yi

Fr.: gravité de surface   

1) The rate at which a small object in free fall near the surface of a body is accelerated by the gravitational force of the body: g = GM / R2, where G is the gravitational constant, and M and R are the mass and radius of the object. The surface gravity of Earth is equal to 980 cm s-2.
2) → black hole surface gravity.

surface; → gravity.


Fr.: susceptibilité   

State or character of being susceptible. → magnetic susceptibility

M.L. susceptibilitas, from susceptibilis "capable, sustainable, susceptible," from susceptus, p.p. of suscipere "sustain, support, acknowledge," from sub "up from under" + capere "to take" ......

Barxodgiri, from bar- "up; upon; on; in; into; at; forth; with; near; before; according to" (Mid.Pers. abar; O.Pers. upariy "above; over, upon, according to;" Av. upairi "above, over," upairi.zəma- "located above the earth;" cf. Gk. hyper- "over, above;" L. super-; O.H.G. ubir "over;" PIE base *uper "over") + xod "self, own" (Mid.Pers. xwad "self; indeed;" Av. hva- "self, own") + giri vebal noun of gereftan "to take, seize, hold" (Mid.Pers. griftan, gir- "to take, hold, restrain;" O.Pers./Av. grab- "to take, seize," cf. Skt. grah-, grabh- "to seize, take," graha- "seizing, holding, perceiving," M.L.G. grabben "to grab," from P.Gmc. *grab, E. grab "to take or grasp suddenly;" PIE *ghrebh- "to seize").


Fr.: durabilité   

An ecological concept, the property or condition of being → sustainable.

Quality, state noun from → sustainable.

tangential velocity
  تندای ِ سایانی   
tondâ-ye sâyâni

Fr.: vitesse tangentielle   

1) The instantaneous linear velocity of a body moving in a circular path. It is equal to the → angular velocity multiplied by the radius: vt = ωr.
3) The component of the velocity of an object, such as a star, that is at right-angles to the observer's → line of sight; also known as transverse velocity. See also → radial velocity.

tangential; → velocity.

Taylor-Couette instability
  ناپایداری ِ تیلر-کویءت   
nâpâydâri-ye Taylor-Couette

Fr.: instabilité de Taylor-Couette   

A hydrodynamic instability in the → Taylor-Couette flow that arises when the rotation velocity of the fluid exceeds a critical value. The instability arises for → Taylor numbers larger than about 1700. At the beginning the fluid elements will move in simple rolls, but turbulence in the form of complex spirals will appear with increasing rotation velocity.

Taylor-Couette flow; → instability.


Fr.: temporalité   

Temporal character or nature.

temporal; → -ity.

tensor density
  چگالی ِ تانسور   
cagâli-ye tânsor

Fr.: densité de tenseur   

A generalization of the tensor concept that like a tensor transforms, except for the appearance of an extra factor, which is the → Jacobian matrix of the transformation of the coordinates, raised to some power, in transformation law. The exponent, which is a positive or negative integer, is called the weight of the tensor density. → weight of a tensor density. Ordinary tensors are tensor densities of weight 0. Tensor density is also called → relative tensor.

tensor; → density.

terminal velocity
  تندای ِ پایانی   
tondâ-ye pâyâni

Fr.: vitesse terminale   

1) The constant maximum velocity reached by a body falling under gravity through a liquid or gas, especially the atmosphere. The body ceases to accelerate downward because the force of gravity is equal to the opposing force of resistance by the medium.
2) The velocity acquired at the end of a body's motion.
3) The velocity attained by → stellar wind at very large distance from the star. The material that escapes from the outer layers of the stars is accelerated outward from a small radial velocity at the → photosphere of the star, to some high velocity at large distance from the star. The theory of → radiation-driven winds predicts that the terminal velocity scales with the → escape velocity as: v  ≅ 2-3 vesc. The winds of hot → O stars experience fast acceleration and reach 80% of their terminal velocity near the star (some 3 R*). The terminal velocity ranges from about 10 km s-1 for a cool → supergiant star to 3000 km s-1 for a luminous hot star. Terminal velocities are quite accurately measured from the violet trough of saturated → P Cygni line profiles in the ultraviolet (mainly N V λ1239, C IV λ1548, Si IV λ1394).

terminal; → velocity.

âzmunpaziri (#)

Fr.: testabilité   

The state or fact of being → testable. See also → falsifiability.

testable; → -ity.

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