An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 27 Search : length
blaze wavelength
  موج-طول ِ بلیز   
mowjtul-e beliz

Fr.: longueur d'onde de blaze   

The wavelength in a given diffraction order for which the efficiency curve reaches its maximum.

blaze; → wavelength.

Mowjtulwavelength; belizblaze.

center wavelength
  موج-طول ِ مرکز   
mowjtul-e markaz

Fr.: longueur d'onde centrale   

Center of a filter passband measured at 50% of peak transmittance.

center; → wavelength.

central wavelength
  موج-طول ِ مرکزی   
mowjtul-e markazi

Fr.: longueur d'onde centrale   

1) In an interference filter, the wavelength of peak transmission.
2) In a spectrograph, the wavelength corresponding to the middle of the range covered by the grating or grism.

Central, adj. from → center; → wavelength.

coherence length
  درازا‌ی ِ همدوسی   
derâzâ-ye hamdusi

Fr.: longueur de cohérence   

The distance over which an electromagnetic wave train maintains a specified degree of coherence.

coherence; → length.

Compton wavelength
  موج-طول ِ کامپتون   
mowjtul-e Compton, tul-e mowj-e ~

Fr.: longueur d'onde de Compton, longueur d'onde Compton   

The quantum wavelength of a particle with a highly relativistic velocity. The Compton wavelength is given by h/mc, where h is Planck's constant, m is the mass of the particle, and c the light speed. For an electron, the Compton wavelength is about 2.4 × 10-10 cm, intermediate between the size of an atomic nucleus and an atom.

Compton; → wavelength.

cutoff wavelength
  موج-طول ِ بره   
mowj-tul-e boré

Fr.: longueur d'onde de coupure   

Wavelength at which the transmittance of a filter, or the detectivity of a detector, has fallen to one-half its peak value.

cutoff; → wavelength.

de Broglie wavelength
  موج-طول ِ دوبروی   
mowjtul-e de Broglie

Fr.: longueur d'onde de Broglie   

The wavelength of the wave associated with a → particle as given by the → de Broglie equation.

de Broglie equation; → wavelength.

Debye length
  درازای ِ دبی   
derâzâ-ye Debye (#)

Fr.: longueur de Debye   

A characteristic length scale in a → plasma, determined by the temperature and number density of the charged particles. The Debye length (in cm) is given by the expression: λD = 743(Te/ne)1/2, where Te is the electron temperature in → electron-volts and ne is the electron density in cm-3. Particles which pass each other at distances smaller than the Debye length interact directly. Outside the Debye length particle interactions are dominated by collective effects. In typical laboratory plasmas the Debye length is small compared with the plasma dimension, so that collective effects are important.

debye (D); → length.

effective focal length
  درازا‌ی ِ کانونی ِ ا ُسکرمند   
derâzâ-ye kânuni-ye oskarmand

Fr.: longueur focale effective   

The focal length of an imaging system, which consists of several lenses or mirrors.

effective; → focal length.

focal length
  درازای ِ کانونی   
derâzâ-ye kânuni

Fr.: longueur focale   

The distance between the optical center of a lens, or the surface of a mirror, and its focus.

focal; → distance.

frequency to wavelength conversion
  هاگرد ِ بسامد به موج-طول   
hâgard-e basâmad bé mowj-tul

Fr.: conversion fréquence / longueur d'onde   

Deriving the → wavelength of an undulatory phenomenon from its → frequency, and vice versa.
1) For → electromagnetic waves: λ = c / f, where λ is the wavelength, c is the → speed of light in → meters per second and f the frequency in → hertz. It can be written as: λ (m) = 2.998 × 108 / f (Hz).
2) For → sound waves: λ = C / f, where C is the → sound speed. For air at temperature 0°C, λ (m) = 332 / f (Hz).

frequency; → wavelength; → conversion.

Hubble length
  درازای ِ هابل   
derâzâ-ye Hubble

Fr.: longueur de Hubble   

The distance traveled by light along a straight → geodesic in one → Hubble time. Also called the → Hubble radius, → Hubble distance, and → cosmic horizon.

Hubble; → length.

Jeans length
  درازای ِ جینز   
derâzâ-ye Jeans (#)

Fr.: longueur de Jeans   

The critical size of a homogeneous and isothermal interstellar cloud above which the cloud is unstable and must collapse under its own gravity. Below this size the cloud's internal pressure is sufficient to resist collapse. The Jeans length is defined by: λJ = (π cs2/Gρ)1/2 = 0.2 pc (T/10 K)1/2(nH2/104 cm-3)-1/2, where cs is the → sound speed, G is the → gravitational constant, ρ is the gas density, T is the gas temperature, and nH2 is the molecular hydrogen density.

Jeans; → length.

  درازا، طول   
derâzâ (#), tul (#)

Fr.: longueur   

A distance determined by the extent of something specified. → Jeans length

M.E. length(e), O.E. lengthu "length," from P.Gmc. *langitho, noun of quality from *langgaz (root of O.E. lang "long," cognate with Pers. derâz, as below) + -itho, abstract noun suffix. Cognate with O.N. lengd, O.Fris. lengethe, Du. lengte.

Derâzâ quality noun of derâz "long," variants Laki, Kurdi derež; Mid.Pers. drâz "long;" O.Pers. dargam "long;" Av. darəga-, darəγa- "long," drājištəm "longest;" cf. Skt. dirghá- "lon (in space and time);" L. longus "long;" Gk. dolikhos "elongated;" O.H.G., Ger. lang; Goth. laggs "long;" PIE base *dlonghos- "long;" tul loan from Ar. ţaul, used in → wavelength.

length contraction
  ترنگش ِ درازا   
terengeš-e derâzâ

Fr.: contraction de longueur   

Same as → Lorentz contraction.

length; → contraction.

kešnâk (#)

Fr.: long, interminable   

1) Having or being of great length; very long.
2) Tediously verbose; very long; too long (

From → length + -y.

Kešnâk "lengthy" (Bardsiri, Kermâni), from kešidan, kašidan "to draw, protract, trail, drag, carry," → tide. Bardesir, Kermân

mixing length
  درازای ِ آمیزش   
derâzâ-ye âmizeš

Fr.: longueur de mélange   

In a → turbulent flow, the average distance traveled by a → convective cell before it dissolves into its surroundings and deposits its energy. The mixing length is of the order of the → pressure scale height (HP), l = αHP, where α is the → mixing length parameter. See also → mixing length theory.

mixing; → length.

mixing length parameter
  پارامون ِ درازای ِ آمیزش   
pârâmun-e derâzâ-ye âmizeš

Fr.: paramètre de la longueur de mémange   

In the → mixing length theory, a parameter, α, that relates the → mixing length, l, to the → pressure scale height: α = l/HP. It is usually supposed that α is of order unity. Changes in α correspond to variations in the efficiency of the → convection, hence the transfer of heat.

mixing; → length; → parameter.

mixing length theory (MLT)
  نگره‌ی ِ درازای ِ آمیزش   
negare-ye derâzâ-ye âmizeš

Fr.: théorie de la longueur de mélange   

A theory dealing with heat transport by → turbulence which includes an elementary treatment of → convection. The central idea is that an unbalanced → buoyancy force drives a → convective cell to move through a distance, called the → mixing length, before the cell dissolves and joins the ambient medium. In this theory an adjustable → mixing length parameter  α is used. The theory, originally due to L. Prandtl (1925), was first applied to the Sun by L. Biermann (1932, Z. Astrophys. 5, 117).

mixing; → length; → theory.

nominal focal length
  درازای ِ کانونی ِ نامین   
derâzâ-ye kânuni-ye nâmin

Fr.: distance focale nominale   

An approximate value of the → focal length, used for the classification of lenses, mirrors, or cameras, as opposed to the measured one.

nominal; → focal; → length.

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