# An Etymological Dictionary of Astronomy and AstrophysicsEnglish-French-Persian

## فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

### M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 29 Search : angular
 angular   زاویه‌ای   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   شتاب ِ زاویه‌ای   šetâb-e zâviye-yiFr.: accélération angulaire   The rate of change of → angular velocity. It is equal to the → first derivative of the → angular velocity: α = dω/dt =d2θ/dt2 = at/r, where θ is the angle rotated, at is the linear tangential acceleration, and r is the radius of circular path.→ angular; → acceleration. angular diameter   ترامون ِ زاویه‌ای، قطر ِ ~   tarâmun-e zâviye-yi, qotr-e ~Fr.: diamètre angulaire   The apparent diameter of an object in angular measure.→ angular; → diameter. angular diameter distance   اپست ِ زاویه‌ای   apest-e zâviye-yiFr.: distance angulaire   1) The ratio of an object's → linear size (l) to its → angular size (δθ, in → radians), that is DA = l/δθ. It is used to convert observed angular separations into proper separations at the source. 2) In cosmology, a distance defined as the ratio of an object's physical transverse size (l) to its angular size (δθ). It is used to convert angular separations in telescope images into proper separations at the source. The angular diameter distance is defined by: DA = l / δθ. Consider a light source of size l at r = r1 and t = t1 subtending an angle δθ at the origin (r = 0, t = t0). The proper distance between the two ends of the object is related to δθ by: δθ = l / [a(t1). r1], where a(t1) is the → scale factor at the present epoch. Therefore, DA = r1 / (1 + z). The angular diameter distance has the particularity that it does not increase infinitely with z→ ∞. It gets its maximum value at a → redshift of ~ 1 and then decreases for higher z. Therefore, more distant objects appear larger in angular size. This is explained by considering the size of the Universe when the light of the object was emitted. At that time the Universe was smaller and therefore the object occupied a larger fraction of the size of the Universe. In other words, objects appear larger because the entire Universe acts as a → gravitational lense.→ angular; → diameter; → distance. angular differential imaging (ADI)   تصویرگری ِ دگرسانه‌ای ِ زاویه‌ای   tasvigari-ye degarsâne-yi-ye zâviye-yiFr.: 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   پاشش ِ زاویه‌ای   pâšeš-e zâvie-yiFr.: 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   اپست ِ زاویه‌ای   apest-e zâviye-yiFr.: 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; → distance. angular frequency   بسامد ِ زاویه‌ای   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; → frequency. angular kinetic energy   کاروژ ِ جنبشی ِ زاویه‌ای   kâruž-e jonbeši-ye zâviye-yiFr.: énergie cinétique angulaier   Same as → rotational energy.→ angular; → kinetic; → energy. angular momentum   جنباک ِ زاویه‌ای   jonbâk-e zâviye-yiFr.: 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. angular momentum catastrophe   نگونزار ِ جنباک ِ زاویه‌ای   negunzâr-e jonbâk-e zâviye-yiFr.: 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   پارامون ِ جنباک ِ زاویه‌ای   pârâmun-e jonbâk-e zâviye-yiFr.: 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; → parameter. angular momentum problem   پراسه‌ی ِ جنباک ِ زاویه‌ای   parâse-ye jonbâk-e zâviye-yiFr.: 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. 2) More generally, in star formation studies, the question of the origin of the angular momentum of a star and the evolution of its distribution during the early history of a star. Consider a filamentary molecular cloud with a length of 10 pc and a radius of 0.2 pc, rotating about its long axis with a typical → angular velocity of Ω = 10-15 s-1. At a matter density of 20 cm-3, the cloud is about 1 → solar mass. The cloud collapses to form a star with radius of 6 x 1010 cm. The conservation of angular momentum (∝ ΩR2) requires that as the radius decreases from 0.2 pc to the stellar value, a factor of 107, the value of Ω must increase by 14 orders of magnitude to 10-1 s-1. The star's rotational velocity will be 20% the speed of light and the ratio of → centrifugal force to gravity at the equator will be about 104. Observational data, however, indicate that the youngest stars are in fact rotating quite slowly, with rotational velocities of 10% of the → break-up velocity. The angular momentum problem was first studied in the context of single stars forming in isolation (L. Mestel, 1965, Quart. J. R. Astron. Soc. 6, 161). For more information see, e.g., P. Bodenheimer, 1995, ARAA 33, 199; H. Zinnecker, 2004, RevMexAA 22, 77; R. B. Larson, 2010, Rep. Prog. Phys. 73, 014901, and references therein.→ angular; → momentum; → problem. angular momentum transfer   تراوژ ِ جنباک ِ زاویه‌ای   tarâvaž-e jonbâk-e zâviye-yiFr.: 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; → transfer. angular momentum transport   ترابرد ِ جنباک ِ زاویه‌ای   tarâbord-e jonbâk-e zâviye-yiFr.: transfert de moment angulaire   Same as → angular momentum transfer.→ angular; → momentum; → transport. angular power spectrum   بیناب ِ توانی ِ زاویه‌ای   binâb-e tavâni-ye zâviye-yiFr.: 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; → power; → spectrum. angular resolution   واگشود ِ زاویه‌ای   vâgošud-e zâviye-yiFr.: 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   جدایی ِ زاویه‌ای   jodâyiye zâviye-yiFr.: séparation angulaire   Same as → angular distance.→ angular; → separation. angular size distance   اپست ِ زاویه‌ای   apest-e zâviye-yiFr.: distance angulaire   Same as → angular diameter distance.→ angular; → size; → distance. angular velocity   تندا‌ی ِ زاویه‌ای   tondâ-ye zâviye-yiFr.: vitesse angulaire   A measure of the angular displacement per unit time. Of a particle traveling on a circular path or a rotating body, the ratio of the angle traversed to the amount of time it takes to traverse that angle: ω = dθ/dt. For a rigid body, all lines in it rotate through the same angle in the same time, and the angular velocity is the characteristic of the body as a whole. The angular velocity is related to the linear velocity by the equation v = rω, where r is the distance of the point from the rotation axis. → vector angular velocity.→ angular; → velocity.

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