An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 902
Angstrom unit (Å)
  یکا‌ی ِ آنگستروم   
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.

zâviye-yi (#)

Fr.: angulaire   

Having, forming, or consisting of an → angle or angles.

From L. angularis "having corners or angles," from angulusangle.

Zâviye-yi, adj. from zâviyé, → angle.

angular acceleration
  شتاب ِ زاویه‌ای   
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
  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-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.
2) In a → homogeneous Universe the angular diameter distance is solely a function of → redshift. In inhomogeneous cosmologies, → gravitational lensing by intervening metric fluctuations can cause magnification of the angular size - with associated change of flux density, since surface brightness is unaffected by lensing. Thus the apparent distance to objects at a given z becomes in effect a randomly fluctuating quantity.

angular; → diameter; → distance.

angular differential imaging (ADI)
  تصویرگری ِ دگرسانه‌ای ِ زاویه‌ای   
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
  پاشش ِ زاویه‌ای   
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
  اپست ِ زاویه‌ای   
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; → 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-yi

Fr.: énergie cinétique angulaier   

Same as → rotational energy.

angular; → kinetic; → energy.

angular momentum
  جنباک ِ زاویه‌ای   
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.

angular momentum catastrophe
  نگونزار ِ جنباک ِ زاویه‌ای   
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
  پارامون ِ جنباک ِ زاویه‌ای   
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; → parameter.

angular momentum problem
  پراسه‌ی ِ جنباک ِ زاویه‌ای   
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.
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-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; → transfer.

angular momentum transport
  ترابرد ِ جنباک ِ زاویه‌ای   
tarâbord-e jonbâk-e zâviye-yi

Fr.: transfert de moment angulaire   

Same as → angular momentum transfer.

angular; → momentum; → transport.

angular power spectrum
  بیناب ِ توانی ِ زاویه‌ای   
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; → power; → spectrum.

angular resolution
  واگشود ِ زاویه‌ای   
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
  جدایی ِ زاویه‌ای   
jodâyiye zâviye-yi

Fr.: séparation angulaire   

Same as → angular distance.

angular; → separation.

angular size distance
  اپست ِ زاویه‌ای   
apest-e zâviye-yi

Fr.: distance angulaire   

Same as → angular diameter distance.

angular; → size; → distance.

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