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: 1965 Search : ion
physical dimension
  وامون ِ فیزیکی   
vâmun-e fiziki

Fr.: dimension physique   

Any of basic physical quantities, such as mass, length, time, electric charge, and temperature in terms of which all other kinds of quantity can be expressed.

physical; → dimension.

physical libration
  هلازان ِ فیزیکی، رخگرد ِ ~   
halâzân-e fiziki, roxgard-e ~

Fr.: libration physique   

A real periodic variation in the rotation rate of a celestial object, as distinct from a → geometrical libration. In particular, slight oscillations in the → Moon's rotation caused by the → gravitational attraction of the Earth on the → equatorial bulge of the Moon's near side. The Moon's physical libration is about 0.03° in longitude and about 0.04° in latitude.

physical; → libration.

physisorption
  فیزی-شمش   
fizi-šameš

Fr.: physisorption   

A kind of → adsorption in which the forces involved are → intermolecular  → van der Waals forces. Same as → physical adsorption. See also → chemisorption.

Physi-, from → physical; → sorption.

piecewise continuous function
  کریای ِ پیوسته‌ی ِ تکه‌ای   
karyâ-ye peyvaste-ye tekke-yi

Fr.: fonction continue par morceaux   

A function f(x) in an interval if :1) the interval can be divided into a finite number of pieces in each of which f(x) is continuous, and 2) the limits of f(x) as x approaches the boundary point of each piece are finite. In other words, a piecewise continuous function is one that is made up of a finite number of continuous pieces.

piecewise; → continuous; → function.

pincushion distortion
  چولگی ِ بالشتکی   
cowlegi-ye bâleštaki

Fr.: distorsion en coussinet   

An → aberration of a → lens  → system in which → magnification increases with → distance from the → optical axis, whereby → horizontal and → vertical lines bend inward toward the → center of the → field. Opposite of → barrel distortion.

Pincushion, from pin, from M.E. pinne, O.E. pinn "peg;" cf. D. pin, Ger. Pinne; perhaps from L. pinna "feather, quill" + cushion, M.E. cuisshin, O.Fr. coissin (Fr. coussin) a variant of V.L. *coxinum, either from L. coxa "hip, thigh," or from L. culcita "mattress;" → distortion.

Cowlegi, → distortion; bâleštaki, adj. of bâleštak, diminutive of bâlešt, variant bâleš "cushion, pillow," Mid.Pers. bâlišn, bâlên "cushion, pillow;" Av. barəiš- "pillow, cushion;" cf. Skt. barhis- "straw, a bed or layer of kusa grass strewed over the sacrificial ground."

pion
  پیون   
piyon (#)

Fr.: pion   

An unstable nuclear particle of mass intermediate between that of a proton and an electron; also called π meson.

From pi (meson) + → -on.

place-value notation
  نمادگان ِ جا-ارزشی   
nemâdgân-e jâ-arezeši

Fr.: notation positionnelle   

A mathematical notation system in which the → numerals get different values depending on their position relative to the other numerals. Same as → positional notation and → positional number system.

place; → value; → notation.

Planck distribution
  واباژش ِ پلانک   
vâbâžeš-e Planck

Fr.: distribution de Planck   

The distribution of radiation with wavelength for a blackbody, given by → Planck's radiation law.

Planck; → distribution.

Planck function
  کریای ِ پلانک   
karyâ-ye Planck

Fr.: fonction de Planck   

Same as → Planck's blackbody formula.

Planck; → function.

Planck's radiation law
  قانون ِ تابش ِ پلانک   
qânun-e tâbeš-e Planck

Fr.: loi du rayonnement de Planck   

An equation that expresses the energy radiated per unit area per unit time per unit wavelength range by a blackbody as a function of temperature. It is expressed by → Planck's blackbody formula.

Planck; → radiation; → law.

plane of polarization
  هامن ِ قطبش   
hâmon-e qotbeš

Fr.: plan de polarisation   

In a → linearly polarized light, a plane perpendicular to the → plane of vibration and containing the direction of propagation of light. It is also the plane containing the direction of propagation and the magnetic vector (H) of the electromagnetic light wave.

plane; → polarization.

plane of rotation
  هامن ِ چرخش   
hâmon-e carxeš

Fr.: plan de rotation   

For a rotating object, the plane → perpendicular to the → rotation axis.

plane; → rotation.

plane of vibration
  هامن ِ شیوش   
hâmon-e šiveš

Fr.: plan de vibration   

In a → linearly polarized light, a plane perpendicular to the → plane of polarization and containing the direction of propagation of light. It is also the plane containing the direction of propagation and the electric vector (E) of the electromagnetic light wave.

plane; → polarization.

plane polarization
  قطبش ِ هامنی   
qotbeš-e hâmoni

Fr.: polarisation plane   

Same as → linear polarization.

plane; → polarization.

planetary aberration
  بیراهش ِ سیاره‌ای   
birâheš-e sayyâreyi

Fr.: aberration planétaire   

The difference between the true position of a planet and its apparent position, due to the time required for light to travel the distance from the planet to Earth. Correction for planetary aberration is necessary in determining orbits.

planetary; → aberration.

planetary precession
  پیشایان ِ سیاره‌ای   
pišâyân-e sayyâre-yi

Fr.: précession planétaire   

The motion of the → ecliptic plane caused by the gravitational influence of the other planets, mainly → Jupiter. The observational effect of planetary precession is similar to that of the → lunisolar precession. But planetary precession causes the → equinoxes to move along the ecliptic in the opposition direction (eastward) from that of luni-solar precession (westward) and at a much slower rate: 0''.12 per year. Same as → precession of ecliptic.

planetary; → precession.

PLAnetary Transits and Oscillations of stars (PLATO)
  پلاتو   
PLATO

Fr.: PLATO   

A space observatory under development by the → European Space Agency for launch around 2024. Its objective is to detect and characterize → exoplanets by means of their → transit signature in front of a very large sample of → bright stars, and measure the seismic oscillations (→ asteroseismology) of the parent stars orbited by these planets in order to understand the properties of the exoplanetary systems.

planetary; → transit; → oscillation; → star.

plasma oscillation
  نوِش ِ پلاسما   
naveš-e plâsmâ

Fr.: oscillation de plasma   

The oscillatory motion of electrons in a neutral plasma around their equilibrium position while the ions remain at rest. When electrons are displaced by any kind of perturbation with respect to ions, a pair of positive and negative charged regions is formed. The Coulomb force accelerates back the displaced electrons, which get kinetic energy. The electrons overshoot their original positions by the same amount as their first displacement.

plasma; → oscillation.

plastic deformation
  وادیسش ِ شوکایند   
vâdiseš-e šukâyand

Fr.: déformation plastique   

Permanent → deformation of a → solid subjected to a → stress.

plastic; → deformation.

Pleione
  پلیونه   
Pleyoné (#)

Fr.: Pléioné   

A star in the constellation → Taurus and a member of the → Pleiades star cluster. Pleione is a blue-white B-type → main sequence → dwarf with a mean apparent magnitude of +5.09. It is a variable star and its brightness varies from magnitude +4.77 to +5.50. It is approximately 380 light-years from Earth.

Pleione was an Oceanid nymph. She lived in a southern region of Greece called Arcadia, on a mountain named Mount Kyllini. She married Atlas and gave birth to the Hyades, Hyas and the Pleiades.

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