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

The electromagnetic radiation emitted by high-energy particles that are moving in magnetic fields, as in a synchrotron particle accelerator. The acceleration of the moving charges causes the particles to emit radiation. Radio galaxies and supernova remnants are intense sources of synchrotron radiation. Characteristics of synchrotron radiation are its high degree of polarization and nonthermal spectrum.

→ synchrotron; → radiation.

A method of dividing a polynomial in the special case of dividing by a linear factor. Synthetic division allows one to do long division problems much quicker. It is related to the → Ruffini-Horner method.

→ synthetic; → division.

A → stellar association containing many → T Tauri stars. Examples include the Taurus-Auriga T association, the nearby → TW Hydrae association, and Vela T1 and T2.

T, letter of alphabet; → association.

That component of a an object's motion which is perpendicular to the observer's → line of sight.

→ tangential; → motion.

Fluid mechanics: A second order differential equation that governs the vertical structure of a perturbation in a stratified parallel flow.

Named after G. I. Taylor (Effect of variation in density on the stability of superposed streams of fluid, 1931, Proc. R. Soc. Lond. A, 132, 499), → Taylor number, and S. Goldstein (On the stability of superposed streams of fluids of different densities, 1931, Proc. R. Soc. Lond. A, 132, 524); → equation.

Meteo.: A reversal in the normal temperature decrease, the temperature rising with increased elevation in the atmosphere instead of falling. A layer in which temperature increases with altitude.

→ temperature; → inversion.

The measure of the ability of an observing system to clearly separate events in time. In other words, the shortest time interval that can be determined between two different events.

→ temporal hour; → resolution.

General: The act of stretching or straining; the state of being stretched or strained.
Mechanics: The longitudinal deformation of an elastic body that results in its elongation.
Electricity: Voltage or potential; electromotive force.

M.E., from M.Fr. tension, from L. tensionem (nominative tensio) "a stretching," from tensus, p.p. of tendere "to stretch," cognate with Pers. taneš, as below.

Taneš, verbal noun from tanidan "to spin, twist, weave;" Mid.Pers. tanitan; Av. tan- to stretch, extend;" cf. Skt. tan- to spin, stretch;" tanoti "stretches," tantram "loom;" Gk. teinein "to stretch, pull tight;" L. tendere "to stretch;" PIE base *ten- "to stretch"), Pers. târ "string," tân "thread," tur "fishing net, net, snare," and tâl "thread" (Borujerdi dialect) belong to this family; variants tanta "cobweb," tanadu, tafen, kartané, kârtané, kâtené, Pashtu tanistah "cobweb;" cf. Skt. tantu- "cobweb, thread, string."

An operation of tensor algebra that is obtained by setting unlike indices equal and summing according to a summation convention.

→ contraction; → tensor.

The perturbation in the → primordial Universe plasma caused by → gravitational waves. These waves stretch and squeeze space in orthogonal directions and bring about → quadrupole anisotropy in incoming radiation temperature.

→ tensor; → perturbation.

A → shock wave inside the → heliopause where the → supersonic → solar wind abruptly slows from an average speed of 500 km s^-1 to → subsonic and becomes denser and hotter.

Termination, verbal noun from terminate, from → term; → shock.

Toš, šok, → shock; pâyâni, → terminal.

A parameter representing the product of the → gravitational constant by the Earth's mass. It is 3.987 x 10¹⁴ m³s^-2 or 3.987 x 10⁵ km³s^-2.

→ terrestrial; → gravitational; → constant.

The act or process of thematizing.

→ thematize; → -tion.

1) The random movement of the molecules of a substance, the energy of which is, by kinetic theory, synonymous with the heat content of the substance.
2) Solid state physics: The random motion of free electrons in a conductor due to heat energy.

→ thermal; → agitation.

A process that occurs in a medium where a → temperature gradient exists: dQ = -κ(dT/dx)dA.dt, where dQ is the amount of heat passing through the time dt across an area dA in the direction of the normal x to this area and toward the reduction in temperature, κ is the → thermal conductivity, and (dT/dx) the temperature gradient.

→ thermal; → conduction.

A physical process resulting from → temperature gradients in stellar interiors, whereby more highly charged and more massive chemical species are concentrated toward the hottest region of the star, its center. Therefore, thermal diffusion and → gravitational settling tend to make heavier species sink relative to the light ones.

→ thermal; → diffusion.

→ thermal radiation.

→ thermal; → emission.

A process in which collisions that occur between particles cause atoms or molecules to obtain additional kinetic energy.

→ thermal; → excitation.

The change in dimensions of a material resulting from a change in temperature.

→ thermal; → expansion.

The random motions and collisions of molecules, atoms, electrons, or other subatomic particles constituting an object at all temperatures above → absolute zero. The thermal motion of particles rises with the temperature of those particles and is governed by the laws of → thermodynamics. The most convincing experimental proof of thermal motion → Brownian motion.

→ thermal; → motion.