An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 1002
pointing model
  مدل ِ آماجش   
model-e âmâješ

Fr.: modèle de pointage   

A mathematical model that reproduces the diurnal rotation of the Earth and is used to direct a telescope toward a precise position on the sky.

pointing; → model.

poise
  پو‌آز   
poise

Fr.: poise   

The unit of viscosity in the c.g.s. system, equal to 1 dyne.s/cm2. Symbol: P

Poise, from Jean-Louis-Marie Poiseuille (1797-1869), a French physiologist and physician who studied the flow of liquids through tubes and developed a method for measuring blood pressure.

Poiseuille's law
  قانون ِ پو‌آزوی   
qânun-e Poiseuille

Fr.: loi de Poiseuille   

In fluid dynamics, the law that the rate of flow of a liquid through a horizontal tube of uniform radius is directly proportional to the pressure of the liquid and the fourth power of the radius of the tube and is inversely proportional to the viscosity of the liquid and the length of the tube.

Named after Jean-Louis-Marie Poiseuille (1797-1869), a French physiologist and physician who found the law in 1844; → law.

Poisson distribution
  واباژش ِ پو‌آسون   
vâbâžeš-e Poisson

Fr.: distribution de Poisson   

A → probability function that characterizes → discrete  → random events occurring independently of one another within some definite time or space. It may be regarded as an approximation of the → binomial distribution when the number of events becomes large and the probability of success becomes small. The Poisson distribution is expressed by: f(x) = (λxe)/x!, where λ is the mean number of successes in the interval, e is the base of the → natural logarithm, and x is the number of successes we are interested in.

Named after Siméon Denis Poisson (1781-1840), French mathematician, who developed the application of Fourier series to physical problems and made major contributions to the theory of probability and to the calculus of variations; → distribution.

Poisson's equation
  هموگش ِ پو‌آسون   
hamugeš-e Poisson

Fr.: équation de Poisson   

An equation (∇2φ = 4πGρ) which relates the gravitational (or electromagnetic) potential to the mass density (or charge density).

Poisson distribution; → equation.

polar
  ۱) قطبی؛ ۲) پلار   
1) qotbi; 2) polâr

Fr.: 1) polaire; 2) polar   

1) Of or pertaining to the pole of any sphere, a magnet, an electric cell, etc.
2) A subclass of → cataclysmic variables, the prototype being AM Herculis. Polars are short-period systems in which a → late-type → main sequence star transfers mass to a highly magnetized → white dwarf. The strong magnetic field (10-70 million → gauss) prevents the formation of an → accretion disk, locks both stars in synchronous rotation and guides the accreting matter to accretion spots which are the source of intense X-ray radiation (material impacts on to the white dwarf where it is radiated away).

1) Adj. of → pole.
2) From polar(ization) + (st)ar, because of their → circularly polarized light.

polar alignment
  آخطش ِ قطبی   
âxateš-e qotbi

Fr.: alignement polaire   

The process or the state of making a → telescope's → polar axis → parallel to the → Earth's → rotation axis, that is with the → true North or → South  → celestial pole. When this is accomplished, the sky's motion can be cancelled out simply by turning the axis (either by hand or with a motor → drive) at the same rate as the rotation of the Earth, but in the opposite direction.

polar; → alignment.

polar axis
  آسه‌ی ِ قطبی   
âse-ye qotbi (#)

Fr.: axe polaire   

The axis of an → equatorial mounting that is parallel to the Earth's axis, and consequently points to the celestial pole.

polar; → axis.

polar bond
  بند ِ قطبی   
band-e qotbi

Fr.: lien polaire   

A chemical bond where the electrons are shared unequally between atoms. The atom that is more electronegative will pull the electrons closer to itself.

polar; → bond.

polar cap
  کلاهک ِ قطبی   
kolâhak-e qotbi

Fr.: calotte polaire   

1) Either of the regions around the poles of the Earth that are permanently covered with ice.
2) Either of the two regions around the poles of the planet Mars, consisting of frozen carbon dioxide and water ice.
3) An area of a → pulsar's surface from where open magnetic field lines emanate.

polar; → cap.

polar circle
  پرهون ِ قطبی، دایره‌ی ِ ~   
parhun-e qotbi, dâyere-ye ~ (#)

Fr.: cercle polaire   

An imaginary parallel circle on the celestial sphere or on the Earth at a distance of 23°.5 from either poles.

polar; → circle.

polar coordinates
  هم‌آراهای ِ قطبی   
hamârâhâ-ye qotbi (#)

Fr.: coordonnées polaires   

A coordinate system in which the position of any point (M) in a plane is specified by two coordinates: 1) ρ, which expresses the distance from a fixed point (the pole, denoted O), and 2) the number φ, which is the angle formed by the line segment OM and a fixed reference line passing through the pole.

polar; → coordinate.

polar cusp
  تیزه‌ی ِ قطبی   
tize-ye qotbi

Fr.: cuspide polaire   

An area in the Earth's → magnetosphere, where the → magnetosheath plasma has direct access to the → ionosphere.

polar; → cusp.

polar day
  روز ِ قطبی   
ruz-e qotbi (#)

Fr.: jour polaire   

In polar regions, the portion of the year when the Sun is continuously in the sky. Its length changes from twenty hours at the Arctic/Antarctic Circle (latitude 66°33' N or S) to 186 days at the North/South Pole.

polar; → day.

polar distance
  دورای ِ قطبی   
durâ-ye qotbi

Fr.: distance polaire   

The angular distance of an object from a celestial pole. It is equal to 90° minus the object's declination.

polar; → distance.

polar equation
  هموگش ِ قطبی   
hamugeš-e qotbi

Fr.: équation polaire   

An equation for a curve written in terms of the → polar coordinates.

polar; → equation.

polar faculae
  پریسک‌های ِ قطبی   
periskhâ-ye qotbi

Fr.: facules polaires   

Solar faculae occurring in regions of high heliographic latitudes. They are smaller than the main-zone faculae; their shape is point-like or oval. Their lifetimes range from a few minutes to some hours, but the decisive difference from the main-zone faculae lies in their activity cycle. When spots and faculae of the main zone are at minimum, the polar faculae have their maximum activity, and vice versa.

polar; → facula.

polar molecule
  مولکول ِ قطبی   
molekul-e qotbi

Fr.: molécule polaire   

A molecule in which the centers of positive and negative charge distribution do not converge and therefore has a mostly positive charge on one side and a mostly negative charge on the other. Different atoms around a central atom will always be polar molecules. Some polar molecules are H2O, HF, COS, and CH3Cl. Polar molecules are characterized by a → dipole moment.

polar; → molecule.

polar motion
  جنبش ِ قطبی   
jonbeš-e qotbi

Fr.: mouvement du pôle   

The irregularly varying motion of the Earth's pole of rotation with respect to the Earth's crust.

polar; → motion.

polar night
  شب ِ قطبی   
šab-e qotbi

Fr.: nuit polaire   

In polar regions, the portion of the year when the Sun does not rise above the horizon. Its length changes from twenty hours at the Arctic/Antarctic Circle (latitude 66°33' N or S) to 179 days at the North/South Pole.

polar; → day.

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