An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 30 Search : scattering
resonant scattering
  پراکنش ِ باز‌آوا   
parâkaneš-e bâzâvâ

Fr.: diffusion résonante   

The absorption and prompt re-emission of photons of a particular wavelength by an atom. In this process, a photon of exactly the right wavelength (i.e. energy) excites an electron in the atom from one energy level to another. The electron then drops back down to its original energy level more or less immediately, emitting a photon of almost identical energy to the one that was absorbed in the first place, but in some random direction. Resonant scattering applies only to line radiation, unlike other forms of scattering which are of continuous radiation (Oxford Dictionary of Astronomy, 2 ed.).

resonant; → scattering.

parâkaneš (#)

Fr.: diffusion   

The process in which the direction of motion of → particles or → waves is changed randomly because of their → interactions (→ collisions) with other particles of the → medium transversed.
Two parameters govern scattering: 1) the wavelength (λ) of the incident radiation, and 2) the size of the scattering particle (r), usually expressed as the nondimensional size parameter, x = 2πr / λ. The size parameter defines three types of scattering:
1) x much less than 1 (or r much smaller than λ), → Rayleigh scattering;
2) x ~ 1 (or rλ), → Mie scattering; and
3) x much larger than 1 (or r much larger than λ), → geometric scattering.
See also: → atmospheric scattering, → backscattering, → Brillouin scattering, → coherent scattering, → Compton scattering, → elastic scattering, → forward scattering, → last scattering, → last scattering surface, → multiple scattering, → noncoherent scattering, → quasi-single-scattering approximation, → Raman scattering, → scattering angle, → scattering coefficient, → scattering of stars, → selective scattering, → single scattering, → spin-flip scattering, → surface of last scattering, → Thomson scattering.
Related terms: → diffraction; → diffusion; → dispersion; → distribution.

Verbal noun of → scatter.

scattering angle
  زاویه‌ی ِ پراکنش   
zâvie-ye parâkaneš

Fr.: angle de diffusion   

The angle between the → incident radiation on a → particle (such as a water droplet in a rainbow) and the scattered radiation (such as the light ray leaving the droplet). Scattering angle is a function of → impact parameter. In other words, The angle along which the change of direction has taken place, irrespective whether radiation is scattered by particles or reflected (refracted) by a surface.

scattering; → angle.

scattering coefficient
  همگر ِ پراکنش   
hamgar-e parâkaneš

Fr.: coefficient de diffusion   

The fraction of light scattered per unit distance in a medium.

scattering; → coefficient.

scattering of stars
  پراکنش ِ ستارگان   
parâkaneš-e setâregân

Fr.: diffusion des étoiles   

The progressive increase of random motions of → disk stars with increasing stellar → ages. While some initial random motion seems likely in the disturbed conditions of disks when the oldest stars formed, the observation is generally attributed to scattering processes. Both massive gas → clumps and → spiral waves are considered as scattering agents (J. A. Sellwood & J. J. Binney, 2002, astro-ph/0203510 and references therein).

scattering; → star.

selective scattering
  پراکنش ِ گزینشی   
parâkaneš-e gozineši

Fr.: diffusion sélective   

A type of scattering that occurs when certain → particles are more effective at scattering a particular → wavelength of light, as in → Rayleigh scattering.

selective; → scattering.

single scattering
  پراکنش ِ تک   
parâkaneš-e tak

Fr.: diffusion unique, ~ simple   

A type of scattering where photons are scattered only once. Single scattering dominates in → optically thin media, since photons have a high probability of exiting the medium (e.g., a thin cloud) before being scattered again.

single; → scattering.

spin-flip scattering
  پراکنش با وارونی ِ اسپین   
parâkaneš bâ vâruni-ye espin

Fr.: diffusion avec renversement du spin   

Quantum mechanics: The scattering of a particle that reverses the spin direction.

spin; flip, from flip-flap; → scattering.

Parâkaneš, → scattering; "with;" vâruni, noun from vârun, → inverse; espin, → spin.

surface of last scattering
  رویه‌ی ِ واپسین پراکنش   
ruye-ye vâpasin parâkaneš

Fr.: surface de dernière diffusion   

Same as → last scattering surface.

surface; → last; → scattering.

Thomson scattering
  پراکنش ِ تامسون   
parâkaneš-e Thomson (#)

Fr.: diffusion de Thomson   

The classical, → non-relativistic scattering of photons by free charged particles. When an electromagnetic wave is incident on a charged particle, the electric and magnetic components of the wave exert a force on the particle, setting it into motion. As it accelerates, it in turn radiates in all directions. Such scattering is independent of wavelength and equal numbers of photons are scattered forward and backward. Thomson scattering occurs in stellar atmospheres and in any non-relativistic → plasma. Thomson scattering is normally taken as the minimum → opacity.

Thomson; → scattering.

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