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Angstrom unit (Å) yekâ-ye Ângštrom Fr.: unité d'Ångström Unit of length used to describe wavelengths and interatomic distances. 1 Å = 10^{-10} m. Named after Anders Jonas Ångström, Swedish physicist and astronomer who founded the science of spectroscopy and discovered by studying the solar spectrum that there is hydrogen in the Sun's atmosphere; → unit. |
angular zâviye-yi (#) Fr.: angulaire Having, forming, or consisting of an → angle or angles. From L. angularis "having corners or angles," from angulus→ angle. Zâviye-yi, adj. from zâviyé, → angle. |
angular acceleration šetâb-e zâviye-yi (#) Fr.: accélération angulaire The rate of change of → angular velocity: α = ω(dω/dθ), where ω is the angular velocity and θ the rotation angle with respect to the reference axis. → angular; → acceleration. |
angular diameter tarâmun-e zâviye-yi, qotr-e ~ Fr.: diamètre angulaire The apparent diameter of an object in angular measure. |
angular diameter distance apest-e zâviye-yi Fr.: distance angulaire 1) The ratio of an object's → linear size
to its → angular size (in → radians).
It is used to convert observed angular
separations into proper separations at the source. |
angular differential imaging (ADI) tasvigari-ye degarsâne-yi-ye zâviye-yi Fr.: imagerie différentielle angulaire A high-contrast imaging technique that reduces minute temporal and spatial → seeing fluctuations and facilitates the detection of faint point sources, in close separation from their stars. It consists of the acquisition of a sequence of images with an → altazimuth mounting telescope while the instrument field derotator is switched off. This keeps the instrument and telescope optics aligned and allows the field of view to rotate with respect to the instrument. For each image, a reference → point spread function (PSF) is constructed from other appropriately selected images of the same sequence and subtracted to remove quasistatic PSF structure (Marois et al. 2006, ApJ 641, 556). → angular; → differential; → imaging. |
angular dispersion pâšeš-e zâvie-yi Fr.: dispersion angulaire The rate of change of the angles of emergence θ of various wavelengths from a dispersing prism: dθ/dλ. → angular; → dispersion. |
angular distance apest-e zâviye-yi Fr.: distance angulaire Between two points A and B, the angle → subtended by lines drawn from an observing point O to A and B. Same as → angular separation. |
angular frequency basâmad-e zaviye-yi (#) Fr.: fréquence angulaire The number of complete rotations per unit time, expressed in radian per second: ω = 2πν, where ν is the frequency (cycles per second). |
angular kinetic energy kâruž-e jonbeši-ye zâviye-yi Fr.: énergie cinétique angulaier Same as → rotational energy. |
angular momentum jonbâk-e zâviye-yi Fr.: moment angulaire, moment cinétique The product of → moment of inertia and → angular velocity; synonymous with moment of momentum about an axis. Angular momentum is a vector quantity; it is conserved in an isolated system. |
angular momentum catastrophe negunzâr-e jonbâk-e zâviye-yi Fr.: catastrophe du moment angulaire A problem encountered by the → cold dark matter model of galaxy formation. The model predicts too small systems lacking → angular momentum, in contrast to real, observed galaxies. → cusp problem; → missing dwarfs. → angular; → momentum; → catastrophe |
angular momentum parameter pârâmun-e jonbâk-e zâviye-yi Fr.: paramètre de moment angulaire The ratio J/M, where J is the → angular momentum of a → rotating black hole and M the mass of the black hole. |
angular momentum problem parâse-ye jonbâk-e zâviye-yi Fr.: problème de moment angulaire 1) The fact that the Sun, which contains 99.9% of the mass of the
→ solar system, accounts for about 2% of the total
→ angular momentum of the solar system. The problem of outward
→ angular momentum transfer has been a main topic of interest for
models attempting to explain the origin of the solar system. |
angular momentum transfer tarâvaž-e jonbâk-e zâviye-yi Fr.: transfert de moment angulaire A process whereby in a rotating, non-solid system matter is displaced toward (→ accretion) or away from (→ mass loss) the rotation center. See also → magnetorotational instability. |
angular momentum transport tarâbord-e jonbâk-e zâviye-yi Fr.: transfert de moment angulaire Same as → angular momentum transfer. |
angular power spectrum binâb-e tavâni-ye zâviye-yi Fr.: spectre de puissance angulaire Of the → cosmic microwave background radiation, a plot of how much the temperature varies from point to point on the sky versus the angular frequency. This spectrum answers fundamental questions about the nature of the Universe. → cosmic microwave background anisotropy; → dipole anisotropy. |
angular resolution vâgošud-e zâviye-yi Fr.: résolution angulaire Of a telescope, the smallest angle betwwen two → point sources that produces distinct images. It depends on both the wavelength at which observations are made and on the diameter of the telescope. Same as → spatial resolution. → angular; → resolution. |
angular separation jodâyiye zâviye-yi Fr.: séparation angulaire Same as → angular distance. → angular; → separation. |
angular size distance apest-e zâviye-yi Fr.: distance angulaire Same as → angular diameter distance. |
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