An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 3106 Search : on
de-excitation
  فرو انگیزش   
foru-angizeš

Fr.: désexcitation   

Transition from an excited energy state to a lower energy level, as in spectral line formation or particle emission from an atomic nucleus.

From → de- + → excitation.

de-projection
  وا-فراشانش   
vâ-farâšâneš

Fr.: déprojection   

A method for estimating the real orientation of a field and/or related velocities/separations from two-dimensional images.

de-; → projection.

decagon
  ده‌بر، ده‌گوش   
dahbar (#), dahguš (#)

Fr.: décagone   

A ten-sided → polygon. A decagon that is equilateral and equiangular is called a regular decagon. Each angle of a regular decagon is 144°. The central angle subtending any side is 36°. The ratio of the radius to the side of a regular decagon forms the → golden ratio.

deca-; → -gon.

decay constant
  پایای ِ تباهی   
pâyâ-ye tabâhi

Fr.: constante de désintégration   

A constant of proportionality occurring in the formula expressing spontaneous → decay of → radionuclides. The number of atoms decaying is given by N = N0e-kt, where N0 is the number of nuclei in the given volume of the substance at instant t = 0, N is the number of nuclei at t, and k is decay constant. Decay constant is related to → half-life by τ = ln2/k, roughly 0.693/k.

decay; → constant.

deceleration
  واشتاب   
vâšetâb (#)

Fr.: décéleration   

The act or process of moving, or of causing to move, with decreasing speed. Sometimes called negative acceleration.

Verbal noun of decelerate.

deceleration parameter
  پارامون ِ واشتاب   
pârâmun-e vâšetâb

Fr.: paramètre de décéleration   

A parameter designating the rate at which the expansion of the Universe would slow down owing to the braking gravitational effect of the matter content of the Universe. It is expressed by: q(t) = -R(t)R ..(t)/R .2(t), where R(t) represents the size of the Universe at time t. See also → expansion parameter; compare with → acceleration parameter.

deceleration; → parameter.

decimal fraction
  برخه‌ی ِ دهدهی   
barxe-ye dahdahi

Fr.: fraction décimale   

A fraction expressed by using → decimal representation, as opposed to a vulgar fraction. For example, 2/5 is a vulgar fraction; 0.40 is a decimal fraction.

decimal; → fraction.

decimal representation
  نمایش ِ دهدهی   
nemâyeš-e dahdahi

Fr.: représentation décimale   

A representation of a real number between 0 and 1, as written a = d1d2d3 ..., where each di is one of the digits 0, 1, 2, ..., 9. This means that a = d1 x 10-1 + d2 x 10-2 + d3 x 10-3+ ...

decimal; → representation.

decision
  واسون   
vâsun

Fr.: décision   

The act or process of deciding. → rule of decision.

Verbal noun of → decide.

declaration
  روناگش   
runâgeš

Fr.: déclaration   

The act of declaring; announcement.
2) Something that is announced or proclaimed.

Verbal noun of → declare.

declension
  واکیله   
vâkilé

Fr.: déclinaison   

The → inflection of nouns, pronouns, or adjectives for case, number, and gender.

M.E. declenson, declynson (with suffix later assimilated to -sion), from O.Fr. declinaison, from L. declinatio, → declination

declination.

declination
  واکیلش   
vâkileš

Fr.: déclinaison   

1) Angular distance (symbol δ) from the celestial equator. One of the coordinates, with → right ascension, that defines the position of a heavenly body in the equator system. Declination is measured positively (+) north or negatively (-) south of the celestial equator from 0° to 90°.
2) Angle between geographic North and magnetic North (symbol D).

Verbal noun of → decline; → -tion.

declination axis
  آسه‌ی ِ واکیلش   
âse-ye vâkileš

Fr.: axe de déclinaison   

The axis to which the telescope tube is fastened in an → equatorial mounting.

declination; → axis.

declination circle
  پرهون ِ واکیلش، دایره‌ی ِ ~   
parhun-e vâkileš, dâyeré-ye ~

Fr.: cercle de déclinaison   

For a telescope with an → equatorial mounting, a graduated circle attached to the → declination axis that shows the → declination to which the telescope is pointing.

declination; → circle.

decomposition
  واهمنهش   
vâhamneheš

Fr.: décomposition   

The process or the state of breaking down a physical entity or an organic material.

From → de- + → composition.

decompression
  واتنجش   
vâtanješ

Fr.: décompression   

1) A gradual decrease in surrounding → pressure, especially the controlled decrease in pressure that divers undergo after working in deep water or breathing compressed air.
2) Computers: The restoration of compressed electronic data to their full size.

de- + → compression.

deconvolution
  واهماگیش   
vâhamâgiš

Fr.: déconvolution   

A mathematical operation that allows to restore the original input signal, such as an astronomical image or spectrum, to its state before being affected by the → atmospheric turbulence and the → transfer function of the instrument. → convolution.

From → de- + → convolution.

deconvolution algorithm
  خوارزمیک ِ واهماگیش   
xârazmik-e vâhamâgiš

Fr.: logiciel de déconvolution, algorithme ~ ~   

An algorithm used to improve the resolution of an image particularly when the convolving function is well defined. Also called deconvolution code.

deconvolution; → algorithm.

deconvolve
  واهماگیشیدن   
vâhamâgišidan

Fr.: déconvoluer   

Verbal form of → deconvolution.

From → de- + → convolve.

decretion
  وابال   
vâbâl

Fr.: décrétion   

A physical process that is contrary to accretion, referring to the outward direction of the mass flow from a star to its environment.

From → de- "reversal, removal," + -cretion, from L. accretionem (nom. accretio, gen. accretionis) "a growing larger," from stem of accrescere, → accretion.


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