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Rossby number 'adad-e Rossby Fr.: nombre de Rossby A dimensionless number relating the ratio of inertial to Coriolis forces for a given flow of a rotating fluid. It is used in the study of atmospheric motions in planets. In case a small number is involved, cyclones and anticyclones are observed for low and high pressures. When it is large (Venus) the Coriolis force becomes negligible and atmospheric motions are barely affected by planetary rotation. Named after Carl-Gustav Arvid Rossby (1898-1957), a Swedish-American meteorologist who first explained the large-scale motions of the atmosphere in terms of fluid mechanics; → number. |
Rossby parameter pârâmun-e Rossby Fr.: paramètre de Rossby The northward variation of the Coriolis parameter, arising from the sphericity of the Earth. → Rossby number; → parameter. |
Rossby wave mowj-e Rossby Fr.: onde de Rossby A wave on a uniform current in a two-dimensional non-divergent fluid system, rotating with varying angular speed about the local vertical. → Rossby number; → wave. |
Rosseland mean opacity 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 κ_{R}, it is defined by: 1/κ_{R} = (π/4σT^{3}) ∫(1/k_{ν}) (∂B/∂T)_{ν}dν, summed from 0 to ∞, where σ is the → Stefan-Boltzmann constant, T temperature, B(T,ν) the → Planck function, and k_{ν} 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. |
Rossiter-McLaughlin effect oskar-e Rossiter-McLaughlin Fr.: effet Rossiter-McLaughlin A → spectroscopic phenomenon observed when either an → eclipsing binary's → secondary star or an → extrasolar planet is seen to → transit across the face of the → primary body. Because of the rotation of the star, an asymmetric distortion takes place in the → line profiles of the stellar spectrum, which changes during the transit. The measurement of this effect can be used to derive the → alignment of the → orbit of the transiting exoplanet with respect to the → rotation axis of the star. Named after Richard Alfred Rossiter (1886-1977) and Dean Benjamin McLaughlin (1901-1965), American astronomers. |
rotate carxidan (#) Fr.: tourner To turn around an axis. See also → revolve. From L. rotare "to cause to spin, roll, move in a circle," from L. rota "wheel;" cognate with Pers. râh "way, path" (from Mid.Pers. râh, râs "way, street," also rah, ras "chariot;" from Proto-Iranian *rāθa-; cf. Av. raθa- "chariot;" Skt. rátha- "car, chariot," rathyā- "road;" Lith. ratas "wheel;" O.H.G. rad; Ger. Rad; Du. rad; O.Ir. roth; PIE *roto- "to run, to turn, to roll"). Carxidan "to rotate," from carx "every thing performing a circulatory motion; a wheel; a cart;" Mid.Pers. chr "wheel," Parthian cxr "wheel;" Ossetic calx "wheel;" Av. caxra- "wheel;" cognate with Skt. cakra- "wheel, circle; cycle," carati "he moves, wanders;" Gk. kyklos "circle, wheel," polos "axis of a sphere," polein "move around;" L. colere "to dwell in, to cultivate, move around," colonus "farmer, settler;" O.E. hweol "wheel;" Rus. koleso "wheel." |
rotating carxandé, carxân Fr.: en rotation Capable of or having rotation. |
rotating black hole siyahcâl-e carxân Fr.: trou noir en rotation A black hole that possesses angular momentum, as first postulated by Roy C. Kerr in 1963. Opposite of a stationary black hole. → ergosphere. → rotating; → black hole. |
rotating star setâre-ye carxân, ~ carxandé Fr.: étoile en rotation A star that has a non-zero → angular velocity. In a rotating star, the → centrifugal forces reduce the → effective gravity according to the latitude and also introduce deviations from sphericity. In a rotating star, the equations of stellar structure need to be modified. The usual spherical coordinates must be replaced by new coordinates characterizing the → equipotentials. See also → von Zeipel theorem. |
rotation carxeš (#) Fr.: rotation The motion of a body about its axis. Verbal noun of → rotate. |
rotation axis âse-ye carxeš Fr.: axe de rotation The imaginary line around which an object rotates. Same as → rotational axis and → axis of rotation. |
rotation curve xam-e carxeš Fr.: courbe de rotation A plot of the variation in → orbital velocity of stars and → interstellar matter with distance from the center of a → galaxy. A "flat" rotation curve indicates that the mass of the galaxy increases linearly with distance from its center. See also: farsi→ Keplerian rotation curve Rotation; → curve. |
rotation energy kâruž-e carxeš Fr.: énergie de rotation The → kinetic energy of rotational motion of an object. It is expressed by E_{R} = (1/2)Iω^{2}, where I is the → moment of inertia and ω → angular velocity (2π/P). |
rotation frequency basâmad-e carxeš Fr.: fréquence de rotation 1) The number of rotations per unit time of a rotating object. |
rotation period dowre-ye carxeš (#) Fr.: période de rotation The interval of time during which an object turns once about its axis. |
rotation phase fâz-e carxeš Fr.: phase de rotation A position parameter used in → stellar magnetic field studies. Its zero value represents the moment when, during → stellar rotation, the positive → magnetic pole is nearest to the → line of sight. |
rotation-induced turbulence âšubnâki-ye zâyide-ye carxeš, darhâzidé az ~ Fr.: turbulence induite par turbulence A type of → turbulence with motions more vigorous in the horizontal than in the vertical direction occurring in internal radiation zone of → rotating stars. Same as → shear turbulence. → rotation; → induced; → turbulence. |
rotation-powered pulsar (RPP) tapâr-e carxeš-tavân, pulsâr-e ~ ~ Fr.: A → neutron star that is spinning down as a result of → torques from → magnetic dipole radiation and particle emission. RPPs derive their energy primarily from the → rotation of the neutron star. The energy from their → spin-down appears as broad-band pulsations from → radio to → gamma-ray wavelengths and as a → wind of energetic particles flowing into their surrounding → pulsar wind nebulae. Since the discovery of RPPs through their radio → pulsations in 1967, more than 2000 → radio pulsars are now known with periods ranging from a few milliseconds to several seconds (A. K. Harding, 2013, Front. Phys. 8, 679). |
rotation-vibration spectrum binâb-e carxeš-šiveš Fr.: spectre rotation-vibration The spectrum of a molecule resulting from the simultaneous rotation and vibration of its constituent atoms. |
rotational carxeši (#) Fr.: rotationnel Of or pertaining to → rotation. |
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