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: 90 Search : city
recession velocity
  تندای ِ دورشدن   
tondâ-ye dur šodan

Fr.: vitesse d'éloignement   

The velocity with which an object moves away from another object or a reference point.

recession; → velocity.

reciprocity theorem
  فربین ِ دوسویگی   
farbin-e dosuyegi

Fr.: théorème de réciprocité   

1) General: Any theorem that expresses various reciprocal relations for the behavior of some physical systems, in which input and output can be interchanged without altering the response of the system to a given excitation.
2) In classical electromagnetism, the theorem stating that the current in a detector divided by the voltage at the source remains constant when source and detector are interchanged, as long as the frequency and all the impedances are left unchanged.

Reciprocity, from L. reciproc(us) "returning the same way, alternating" + → -ity; → theorem.

Farbin, → theorem; dosuyegi, quality noun of dosuyé nuanced term of dosu "two-sided," from do, → two, + su "direction, side," from Mid.Pers. sôk "direction, side."

relative velocity
  تندای ِ بازانی   
tondâ-ye bâzâni

Fr.: vitesse relative   

For two objects A and B, the velocity which B, supposing itself at rest, assigns to A.

relative; → velocity.

relativistic velocity
  تندای ِ بازانیگی‌مند   
tondâ-ye bâzânigimand

Fr.: vitesse relativiste   

The velocity of a body when it is a significant fraction of the → speed of light.

relativistic; → velocity.

Rosseland mean opacity
  کدری ِ میانگین ِ روسلاند   
kederi-ye miyângin-e Rosseland

Fr.: opacité moyenne de Rosseland   

The → opacity of a gas of given composition, temperature, and density averaged over the various wavelengths of the radiation being absorbed and scattered. The radiation is assumed to be in → thermal equilibrium with the gas, and hence have a → blackbody spectrum. Since → monochromatic opacity in stellar plasma has a complex frequency dependence, the Rosseland mean opacity facilitates the analysis. Denoted κR, it is defined by: 1/κR = (π/4σT3) ∫(1/kν) (∂B/∂T)νdν, summed from 0 to ∞, where σ is the → Stefan-Boltzmann constant, T temperature, B(T,ν) the → Planck function, and kν monochromatic opacity (See Rogers, F.J., Iglesias, C. A. Radiative atomic Rosseland mean opacity tables, 1992, ApJS 79, 507).

Named after Svein Rosseland (1894-1985), a Norwegian astrophysicist, who obtained the expression in 1924; → mean; → opacity.

rotational velocity
  تندای ِ چرخشی   
tondâ-ye catxeši

Fr.: vitesse de rotation   

The velocity of a → rotational motion; same as → angular velocity.

rotational; → velocity.

scientificity
  دانشیگی   
dânešigi

Fr.: scientificité   

The quality of the practices and theories that aim at establishing reproducible regularities in phenomena by using experimental method and providing a clearly formulated description.

scientific + → -ity.

solar metallicity
  فلزیگی ِ خورشیدی   
felezigi-ye xoršidi

Fr.: métallicité solaire   

The proportion of the solar matter made up of → chemical elements heavier than → helium. It is denoted by Z, which represents the sum of all elements heavier than → helium, in mass fraction. The most recent determination of the solar Z gives a value of 0.0134 (Asplund et al. 2009, ARAA 47, 481), corresponding to the present-day photospheric composition.

solar; → metallicity.

solar velocity
  تندای ِ خورشید، ~ خورشیدی   
tondâ-ye xoršid, ~ xoršidi

Fr.: vitesse solaire   

The rate of change of the Sun's position with respect to the local standard of rest toward the → solar apex.

solar; → velocity.

space velocity
  تندای ِ فضایی   
tondâ-ye fazây

Fr.: vitesse spatiale   

The velocity of a star relative to the Sun.

space; → velocity.

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.

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.

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.

thermoelectricity
  دمابرق   
damâbarq (#)

Fr.: thermo-éléctricité   

The electricity produced by heat or temperature difference in a conductor.

thermo- + → electricity.

transverse velocity
  تندای ِ تراگذر   
tondâ-ye tarâgozar

Fr.: vitesse transverse   

Same as → tangential velocity.

transverse; → velocity.

univocity
  یکوازی   
yekvâzi

Fr.: monosémie   

The character of being → univocal. Same as → monosemy.

univocal; → ity.

vector angular velocity
  بردار ِ تندای ِ زاویه‌ای   
bordâr-e tondâ-ye zâviye-yi

Fr.: vecteur de vitesse angulaire   

Of a rotating body, a vector of magnitude ω (→ angular velocity) pointing in the direction of advance of a right-hand screw which is turned in the direction of rotation.

vector; → angular; → velocity.

velocity
  تندا   
tondâ

Fr.: vitesse   

The time rate of change of position in a given direction, measured as length per unit time. → speed.

L. velocitatem (nominative velocitas) "swiftness, speed," from velox (genitive velocis) "swift."

Tondâ, from tond "swift, rapid, brisk; fierce, severe" (Mid.Pers. tund "sharp, violent;" Sogdian tund "violent;" cf. Skt. tod- "to thrust, give a push," tudáti "he thrusts;" L. tundere "to thrust, to hit" (Fr. percer, E. pierce, ultimately from L. pertusus, from p.p. of pertundere "to thrust or bore through;" PIE base *(s)teud- "to thrust, to beat") + noun suffix .

velocity curve
  خم ِ تندا   
xam-e tondâ

Fr.: courbe de vitesse   

A plot of the radial velocity of an object against time, derived from the Doppler shift of spectral lines.

velocity; → curve.

velocity dispersion
  پاشش ِ تندا   
pâšeš-e tondâ

Fr.: dispersion de vitesses   

The → standard deviation of a velocity → distribution. It indicates how objects of the sample move relative to one another. Objects with similar velocities have a small velocity dispersion, whereas objects with very different velocities have a large velocity dispersion.

velocity; → dispersion.

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