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reddened star setâre-ye sorxidé Fr.: étoile rougie A star whose light has undergone → reddening. |
reddening sorxeš Fr.: rougissement The process by which light from an astronomical object grows red as it travels through interstellar dust. Dust scatters blue light more than red, thus leaving predominantly red light transmitted. Verbal noun of → redden. |
reddening coefficient hamgar-e sorxeš Fr.: coefficient de rougissement A dimensionless quantity determined from the comparison of the observed → Balmer decrements with respect to the theoretical values for given physical conditions of electron temperature and density. The reddening coefficient at Hβ is defined as c(Hβ) = log (I(Hβ)/F(Hβ)), where I(Hβ) and F(Hβ) are → de-reddened and reddened Hβ fluxes respectively. Also called logarithmic extinction. → reddening; → coefficient. |
reddening function karyâ-ye sorxeš Fr.: fonction de rougissement The normalized interstellar extinction at a given wavelength. It is defined by f(λ) = A(λ)/A(Hβ) - 1, where A(λ) is the extinction at the given wavelength and A(Hβ) the extinction at Hβ, with f(Hβ) = 0. It is used to → de-redden observed fluxes: I(λ)/I(Hβ) = F(λ)/F(Hβ).10^{c(Hβ).f(λ)}, where I represents the flux in the absence of extinction and F the observed flux affected by extinction, c(Hβ) being the → reddening coefficient. |
reddening parameter pârâmun-e sorxeš Fr.: paramètre de rougissement A dimensionless quantity characterizing the → interstellar extinction, defined by the total-to-selective extinction ratio: R_{V} = A_{V}/E(B-V). The typical value found for the reddening parameter in the Milky Way is R_{V} ~ 3.1, but it is known to vary from one line of sight to another, from values as 2 to as large as 6. Very large → dust grains would produce extinction with R_{V} → ∞. |
reddening vector bordâr-e sorxeš Fr.: vecteur de rougissement A vector indicating the direction in which interstellar reddening moves the position of a star in a multi-dimensional space of color indices. |
redshift sorxkib Fr.: décalage vers le rouge A shift in the lines of an object's spectrum toward longer wavelengths. Redshift indicates that an object is moving away from the observer. The larger the redshift, the faster the object is moving. Redshift is expressed by z = Δλ/λ = v/c, where λ is the wavelength, Δλ the wavelength shift, v the velocity of the source relative to the observer, and c the → speed of light. When v approaches c, redshift is expressed by the → relativistic formula z = ((1 +v/c)/(1 - v/c))^{½} - 1. |
redshift space fazâ-ye sorx-kib Fr.: espace de décalage vers le rouge The space corresponding to → redshift measurements, as contrasted with real space. See also → redshift space distortion |
redshift space distortion cowlegi-ye fazâ-ye sorx-kib Fr.: distorsion dûe aux vitesses particulières sur la ligne
de visée The distortion observed in → redshift space of → galaxy clusters caused by peculiar velocities of the members (→ peculiar velocity). In a perfectly homogeneous → Friedmann-Lemaitre Universe the redshifts would accurately measure radial distances from the observer, and the mapping from real space to redshift space would simply be an identity. In an inhomogeneous Universe the peculiar velocities associated with any inhomogeneous structure will introduce a distortion in this mapping (N. Kaiser, 1987, MNRAS 227, 1). See also: → fingers of God, → Kaiser effect. → redshift; → space; → distortion;. |
redshift survey bardid-e sorx kib Fr.: relevé de décalages vers le rouge A survey of a large region of the sky to measure the redshifts of all the galaxies down to a certain limiting magnitude. |
redshift-distance relation bâzâneš-e sorxkib-durâ Fr.: relation décalage vers le rouge-distance The correlation, first established by E. Hubble, between the cosmological recession velocities of galaxies and their distances. |
redshifted line xatt-e sorx kibideh Fr.: raie décalée vers le rouge A spectral line whose wavelength does not coincide with its theoretical value and is shifted toward longer wavelengths. |
reduce 1) bâzhâxtan, bâzhâzidan; 2) kâstan Fr.: réduire 1) To bring to a certain state, condition, arrangement, etc. M.E. reducen "to lead back," from O.Fr. reducer, from L. reducere, from → re- "back" + ducere "to bring, to lead." From bâz-, → re- +
Mid.Pers. hâxtan, hâzidan
"to lead, guide, persuade," Av. hak-, hacaiti "to attach oneself to, to join," cf.
Skt. sacate "accompanies, follows," Gk. hepesthai
"to follow," L. sequi "to follow;" PIE *sekw- "to follow." |
reduced mass jerm-e bâhâzidé Fr.: masse réduite The "effective" → inertial mass appearing in the → two-body problem of → Newtonian mechanics. The reduced mass is a quantity which allows the two-body problem to be solved as if it were a one-body problem. For the masses m_{1} and m_{2}, it is given by the ratio μ = m_{1}m_{2} / (m_{1} + m_{2}). The value of μ is generally smaller than m_{1} and m_{2}. The larger the difference between the two masses, the closer μ will be to the smaller mass. If the particles are of equal mass, μ is half the mass of either. |
reduced Planck's constant pâyâ-ye Planck-e bâzhâzidé Fr.: constante de Planck réduite The Planck's constant divided by 2π and denoted ħ, pronounced h-bar. Also called → Dirac's constant. Reduced, p.p. of → reduce; → Planck's constant. |
reducing agent konešgar-e bâzhâzandé Fr.: réducteur A substance which removes → oxygen from, or adds → hydrogen, to another substance. In the more general sense, one which loses electrons. Also called → reductant. |
reducing atmosphere javv-e bâzhâzandé, havâsepehr-e ~ Fr.: atmosphère réductrice 1) An atmospheric condition in which oxidation is prevented by removal
of oxygen and other oxidating gasses or vapours. Usually nitrogen or
hydrogen gas is used in order to produce specific effects, e.g. on
ceramic wares being fired. Reducing verbal adj. of → reduce; → atmosphere. |
reductant bâzhâzandé Fr.: réducteur Same as → reducing agent. Agent noun from → reduce. |
reductio ad absurdum bâzhâzeš bé yâvé Fr.: raisonnement par l'absurde Logic, Math.: A method of → reasoning in which one assumes some statement to be → true and from that → assumption proceeds to deduce a logical → absurdity and hence to a conclusion that the original assumption must have been → false. L. reductio ad absurdum "reduction to absurdity," → reduction; → absurd. |
reduction bâzhâzeš Fr.: réduction 1) In → data processing, the transformation of data from
a "raw" form to some usable form. Verbal noun of → reduce. |
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