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: 699
rotational angular momentum
  جنباک ِ زاویه‌ای ِ چرخشی   
jonbâk-e zâviyeyi-ye carxeši

Fr.: moment angulaire rotationnel, moment cinétique ~   

The → angular momentum of a body rotating about an axis. The rotational angular momentum of a solid homogeneous sphere of mass M and radius R rotating about an axis passing through its center with a period of T is given by: L = 4πMR2/5T.

rotational; → angular; → momentum.

rotational axis
  آسه‌ی ِ چرخش   
âse-ye carxeš

Fr.: axe de rotation   

An imaginary line about which a solid object rotates. Same as → rotation axis and → axis of rotation.

rotational; → axis.

rotational broadening
  پهنش ِ چرخشی   
pahneš-e carxeši

Fr.: élargissement rotationnel   

The spectral line broadening caused by stellar rotation. Light from two rims of the star will be Doppler shifted in opposite directions, resulting in a line broadening effect. The line broadening depends on the inclination of the star's pole to the line of sight. The derived value is a function of ve. sini, where ve is the rotational velocity at the equator and i is the inclination, which is not always known. The fractional width (Δλ/λ) is of the order of 10-3 for B stars.

rotational; → broadening.

rotational Eddington limit
  حد ِ ادینگتون ِ چرخشی   
hadd-e Eddington-e carxeši

Fr.: limite d'Eddington avec rotation   

The → Eddington limit of luminosity for a → rotating star in which both the effects of → radiative acceleration and rotation are important. Such objects mainly include → OB stars, → LBV, → supergiants, and → Wolf-Rayet stars. It turns out that the maximum permitted luminosity of a star is reduced by rotation, with respect to the usual Eddington limit (Maeder & Meynet, 2000, A&A, 361, 159).

rotational; → Eddington limit.

rotational energy
  کاروژ ِ چرخشی   
kâruš-e carxeši

Fr.: énergie rotationnelle   

The → kinetic energy due to the → rotation of and object. Rotational energy is part of the total kinetic energy of the body. It is given by: (1/2)Iω2, where I is the → moment of inertia and ω is the → angular velocity. Same as → angular kinetic energy.

rotational; → energy.

rotational mixing
  آمیزش ِ چرخشی   
âmizeš-e carxeši

Fr.: mélange rotationnel   

A consequence of → stellar rotation that deforms the star, triggers instabilities (→ shear turbulence and → meridional currents) leading to → transport of chemical species in the star. The efficiency of rotational mixing (measured for instance by the degree of surface → enrichments at a given → evolutionary stage) increases when the initial mass and rotation increase. This efficiency increases also when the initial → metallicity decreases. This is due to the fact that when the metallicity is lower, the stars are more compact. This makes the → gradients of the → angular velocity steeper in the stellar interiors. Steeper gradients produce stronger shear turbulence and thus more mixing. Rotational mixing can bring to the surface heavy elements newly synthesized in the stellar core. Rotation thus produces an increase of the → opacity of the outer layers and activates strong → mass loss through → radiatively driven winds. This effect may be responsible for the loss of large fractions of the initial mass of the star (Meynet et al. 2007, arXiv:0709.2275).

rotational; → mixing.

rotational motion
  جنبش ِ چرخشی   
jonbeš-e charkheshi

Fr.: mouvement de rotation   

Of a → rigid body, a motion in which there are always two points of the body which remain motionless.

rotational; → motion.

rotational period
  دوره‌ی ِ چرخش   
dowre-ye carxeš

Fr.: période de rotation   

rotation period.

rotational; → period.

rotational transition
  گذرش ِ چرخشی   
gozareš-e carxeši

Fr.: transition rotationnelle   

A slight change in the energy level of a molecule due to the rotation of its constituent atoms about their center of mass.

rotational; → transition.

rotational velocity
  تندای ِ چرخشی   
tondâ-ye catxeši

Fr.: vitesse de rotation   

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

rotational; → velocity.

rotator
  چرخنده، چرخاننده   
carxandé (#), carxânandé (#)

Fr.: rotateur   

A device that rotates or causes rotation.

Agent noun from → rotate.

rotor
  چرخا   
carxâ (#)

Fr.: rotor   

A rotating part of an electrical apparatus, e.g. the armature of a generator, or of a mechanical device.
A system of several flat blades attached to a hub, which rotates either horizontally to give lift and thrust to a helicopter, or vertically to help control it.
Meteo.: The circulation of flow about a horizontal or nearly horizontal axis.

Short for rotator, → rotate, + → -or.

Carxâ agent noun of carxidan, → rotate.

row
  رج   
raj (#)

Fr.: ligne, rangée   

CCD detector: Series of pixels arranged along a line. → column

O.E. ræw "a row, line;" cf. Du. rij "row;" O.H.G. rihan "to thread," riga "line;" Ger. Reihe "row, line, series."

Raj "line, row," variants raž, rak, râk, rezg (Lori), ris, risé, radé, rasté, râsté, related to râst "right, true; just, upright, straight;" Mid.Pers. râst "true, straight, direct;" Soghdian rəšt "right;" O.Pers. rāsta- "straight, true," rās- "to be right, straight, true;" Av. rāz- "to direct, put in line, set," razan- "order;" cf. Skt. raj- "to direct, stretch," rjuyant- "walking straight;" Gk. orektos "stretched out;" L. regere "to lead straight, guide, rule," p.p. rectus "right, straight;" PIE base *reg- "move in a straight line," hence, "to direct, rule."

Roxburgh criterion
  سنجیدار ِ راکسبرگ   
sanjidâr-e Roxburgh

Fr.: critère de Roxburgh   

An integral constraint used to quantify the uncertainty on the extent of → convective overshooting and its effect on models of stars.

Roxburgh, I. 1989, A&A, 211, 361; → criterion.

RR Lyrae star
  ستاره‌ی ِ RR چنگ   
setâre-ye RR Cang

Fr.: étoile RR Lyrae   

A member of a large class of yellow pulsating stars of type A2-F6 with periods less than 1 day. They are similar to Cepheids, except that their periods are much shorter and are less luminous. RR Lyrae stars belong to Population II and are often found in globular clusters (hence one of their older names - cluster variables) or elsewhere in the galactic halo. They are used as distance indicators out to more than 200 kpc.

Lyra; → star.

rubidium
  روبیدیوم   
rubidiom (#)

Fr.: rubidium   

A metallic chemical element; symbol Rb. Atomic number 37; atomic weight 85.4678; melting point 38.89°C; boiling point 686°C; specific gravity 1.53 at 20°C. It was discovered in the mineral lepidolite by the German chemist Robert Wilhelm Bunsen and the German physicist Gustav-Robert Kirchoff in 1861. Bunsen isolated rubidium in 1863.

From L. rubidus "deep red," because of the two "deep red lines" in its spectra.

ruby
  یاقوت، یاکند   
yâqut (#), yâkand (#)

Fr.: rubis   

Red form of corundum, Al2O3, which owes its color to traces of chromium. Used in laser as a gem stone.

M.E. rubi, from O.Fr. rubi, from M.L. rubinus lapis "red stone," from L. rubeus "red," related to ruberred.

Yâqut, yâkand related to Gk. hyakinthos "hyacinth," probably ult. from a non-I.E. Mediterranean language.

Rudolphine Tables
  زیج ِ رودولفی   
zij-e Rudolfi

Fr.: Tables rudolphines   

A set of astronomical tables created in 1627 by Johannes Kepler (1571-1630) based on observations by Tycho Brahe (1546-1601). These tables allowed Kepler to derive the three laws of planetary motions bearing his name (→ Kelpler's laws). These are the first tables in which → atmospheric refraction has been taken into account. They overruled the → Prutenic Tables.

From the L. title Tabulae Rudolphinae, in memory of Rudolf II (1552-1612), king of Hungary and Bohemia, and Holy Roman Emperor; → table.

Ruffini-Horner method
  روش ِ روفینی-هورنر   
raveš-e Ruffini-Horner

Fr.: méthode de Ruffini-Horner   

A method for finding the value of a → polynomial given by a real number and deriving its → roots. It consists essentially of factoring the polynomial in a nested form. Also known as → nested multiplication.

Named after Paolo Ruffini (1765-1822) and William Horner (1786-1837), who independently elaborated the method; → method.

Ruhmkorff coil
  پیچه‌ی ِ روهمکورف   
pice-ye Ruhmkorff

Fr.: bobine de Ruhmkorff   

An → induction coil which was a forerunner of today's automobile ignition coil. It consists of two coils wound on a single → iron core, and uses an → alternating current produced by a break-wheel to induce a high-voltage current in the secondary coil.

After Heinrich Daniel Ruhmkorff (1803-1877), a German-born instrument maker, who settled in Paris in 1819 for the rest of his life; → coil.

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