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

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.

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.

The sum total of the physical, mental, emotional, and social characteristics of an individual (Dictionary.com).

→ personal; → -ity.

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

→ phase; → velocity.

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

→ physical; → quantity.

The density corresponding to a → Planck mass in a cubic region of edge length given by the → Planck length: ρ_P = 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.

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.

The state or fact of being plural or numerous.

→ plural + → -ity.

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.

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.

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

→ polarity; → event.

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.

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 = (V_v/V_t) = (1 - V_s/V_t), where V_v and V_s are the volumes of vacuum and of the solid matter making up the particle, and V_t is the total volume of the particle within some defined surface.

→ porous; → -ity.

The state or fact of being possible. Something possible.

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

ŠÃ¢yani, from šÃ¢yan, → possible.

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

→ potential; → density.

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.

Same as → spectral density.

→ power; → spectral; → density.

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.

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.

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.