An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 471 Search : ity
tarâvâyi (#)

Fr.: perméabilité   

The degree of → magnetization of a material that responds linearly to an applied magnetic field. → magnetic permeability.

From permeable, from L. permeabilis "that can be passed through, passable," from L. permeare "to pass through," from per- "through" + meare "to pass," from PIE base *mei- "to change; to go, move."

Tarâvâyi quality noun of tarâvâ "permeable," from tarâvidan "to exude, trickle, ooze; to drop," probably from Proto-Iranian *tra-vaxš-. The first component *tra- "across, over, beyond," → trans-. The second component *vaxš-, cf. Av. uxš-/vaxš- "to sprinkle," present tense stem uxš-; cf. Skt. uks- "to sprinkle, moisten," uksati "spinkles, wets;" Gk. hygros "wet, moist, fluid;" L. uvidus "watery, humid, damp." Tarâvidan may be a back formation from *tarâvaš.


Fr.: permittivité   

A measure of the ability of a material to transmit (or "permit") an electric field. Permittivity is defined as the ratio of the flux density produced by an electric field in a given dielectric to the flux density produced by that field in a vacuum. In → SI units, permittivity is measured in → farads per meter. The constant ε0 is known as the permittivity of free space; its value is about 8.854 x 10-12 F/m.

State or quality noun from → permit.


Fr.: personnalité   

The sum total of the physical, mental, emotional, and social characteristics of an individual (

personal; → -ity.

phase velocity
  تندای ِ فاز   
tondâ-ye fâz

Fr.: vitesse de phase   

The speed at which any fixed phase (individual wave) in a → wave packet travels. It is expressed as vph = ω/k, where ω is the → angular frequency and k the → wave number. See also the → group velocity.

phase; → velocity.

physical quantity
  چندای ِ فیزیکی   
candâ-ye fiziki (#)

Fr.: quantité physique   

A physical → property that can be measured and/or calculated.

physical; → quantity.

Planck density
  چگالی ِ پلانک   
cagâli-ye Planck

Fr.: densité de Planck   

The density corresponding to a → Planck mass in a cubic region of edge length given by the → Planck length: ρP = c5/(ħG2) ≅ 5.16 x 1093 g cm-3, where c is the → speed of light, ħ is the → reduced Planck's constant, and G is the → gravitational constant.

Planck; → density.


Fr.: plasticité   

The property which enables a material to be → deformed permanently without → rupture during the application of a → force. An → elastic material becomes plastic above its → yield point. See also → elasticity, → ductility.

plastic; → -ity.


Fr.: pluralité   

The state or fact of being plural or numerous.

plural + → -ity.


Fr.: polarité   

1) Physics: The condition, in a system, of having opposite characteristics at different points, especially positive or negative with respect to electric charge or magnetic properties.
2) Chemistry: A property of a molecule caused by unsymmetrical charge distribution.

From → polar + → -ity.

polarity epoch
  زیمه‌ی ِ قطبیگی   
zime-ye qotbigi

Fr.: époque de polarité   

The time during which the Earth's magnetic field was of a single polarity; an interval of time between reversals of Earth's magnetic field.

polarity; → epoch.

polarity event
  رویداد ِ قطبیگی   
ruydâd-e qotbigi

Fr.: événement de polarité   

A specific event in the history of Earth's magnetic field. Usually used in reference to a specific → polarity reversal.

polarity; → event.

polarity reversal
  وارونش ِ قطبیگی، واگردانی ِ ~   
v âruneš-e qotbigi, vâgardâni-ye ~

Fr.: inversion de polarité   

1) A change in the → polarity of Earth's magnetic field in which the north magnetic pole becomes the south magnetic pole and vice versa. Also known as geomagnetic reversal or magnetic reversal. Earth's magnetic field has reversed many times in the past and the time intervals between these changes are known as → polarity epochs.
2) The change in the polarity of the → solar magnetic field with the ending of each → solar activity cycle so that the North magnetic pole becomes the South and vice versa.

polarity; → reversal.


Fr.: porosité   

1) General: A → dimensionless number characterizing a porous medium, expressed by the ratio of the volume occupied by the pores to the total volume of the medium.
2) Geology: The percentage volume of hollow spaces in a rock, sediment, or soil.
3) Dust grains: The quantity usually defined as: P = (Vv/Vt) = (1 - Vs/Vt), where Vv and Vs are the volumes of vacuum and of the solid matter making up the particle, and Vt is the total volume of the particle within some defined surface.

porous; → -ity.


Fr.: possibilité   

The state or fact of being possible. Something possible.

M.E. possibilite, from L.L. possibilitas, → possible + → -ity.

ŠÃ¢yani, from šÃ¢yan, → possible.

potential density
  چگالی ِ توند   
cagâli-ye tavand

Fr.: densité potentielle   

Of a fluid parcel at pressure P, the density that it would acquire if adiabatically brought to a reference pressure.

potential; → density.


Fr.: potentialité   

1) The state or quality of being potential. Something potential.
2) According to Aristotle, what has the possibility of having → form, in contrast to → actuality; the power to effect change.

potential + → -ity.

power spectral density
  چگالی ِ بینابی ِ توان   
cagâli-ye binâbi-ye tavân

Fr.: densité spectrale de puissance   

Same as → spectral density.

power; → spectral; → density.

principle of identity
  پروز ِ ایدانی   
parvaz-e idâni

Fr.: principe d'identité   

The first principle of → formal logic introduced in Aristotle's theory of the → syllogism: If a statement is true then it is true. Also called → law of identity.

principle; → identity.

principle of relativistic causality
  پروز ِ بنارمندی ِ باز‌آنیگی‌مند   
parvaz-e bonârmandi-ye bâzânigi-mand

Fr.: principe de la causalité relativiste   

One consequence of the theory of → special relativity, according to which no two events separated by a distance greater than their separation in time multiplied by the → speed of light may have a → causal influence on each other. Violation of this principle leads to → paradoxes, such as that of an → effect preceding its → cause.

principle; → relativistic; → causality.

principle of relativity
  پروز ِ بازانیگی   
parvaz-e bâzânigi

Fr.: principe de relativité   

The first postulate in Einstein's theory of → special relativity whereby all the laws of physics are the same in every → inertial reference frame. In other words, no physical measurement can distinguish one inertial reference frame from another. See also → principle of constancy.

principle; → relativity.

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