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

Of, pertaining to, or consisting in theory.

From L.L. theoreticus "of or pertaining to theory," from Gk. theoretikos "contemplative, pertaining to theory;" → theory.

Negarik, contraction of negaréik, from negaré→ theory + -ik, → -ic.

An astrophysical study or research group mainly concerned with theory rather than observation.

→ theoretical; → astrophysics.

One who formulates or is expert in the theoretical side of a subject.

From theoretic, from theoretics, from → theory + -ian.

Negare-pardâz, from negaré, → theory, + pardâz, present stem of pardâxtan "to accomplish; bring to perfection; to attempt, to care; to clean; to free;" Mid.Pers. pardâxtan, pardâzidan "to accomplish; to be done with, freed of" ultimately from Proto-Iranian *para-tāxta-, *para-tāca- "to take away; to expel," from *para- "along, forth," → para-, + tāxta-, tāca- "to run, to flow;" cf. Av. tak- "to run, to flow;" Mod.Pers. tâxtan, tâz- "to flow, to cause to walk," → flow.

Any of the two theories put forward by Albert Einstein: → special relativity (1905) and → general relativity (1916).

→ theory; → relativity;

The emission of electromagnetic radiation from high temperature plasma, produced as electrons are deviated by positive ions. Same as → free-free emission

→ thermal; → bremsstrahlung.

The ordinary pressure in a gas that is due to motions of particles and can be attributed to the object's → temperature.

→ thermal; → pressure.

A temperature scale, measured in → kelvin (K), that is related to the energy possessed by matter; it was formerly known as → absolute temperature. The zero point on the scale (0 K) is absolute zero. Thermodynamic temperature can be converted to temperature on the → Celsius scale by subtracting 273.15.

→ thermodynamic; → temperature.

A nuclear reaction in which two or more atomic nuclei fuse into a single heavier nucleus by a collision of the interacting particles at extremely high temperatures. Chains of thermonuclear reactions, such as the → proton-proton chain and the → CNO cycle, account for the energy radiated from the Sun and more massive stars.

→ thermo- + → nuclear; → reaction.

The region of the upper atmosphere in which temperature increases continuously with height, starting at roughly 100 km. The thermosphere includes the exosphere and most of the ionosphere.

→ thermo-; → sphere.

A → dredge-up process that occurs in the stellar interior during He shell burning, as in → asymptotic giant branch (AGB) stars. These stars consist of a degenerate carbon-oxygen core, surrounded by a helium-rich region, above which lies a hydrogen-rich convective envelope. Following thermal pulses of the helium-burning shell, the convective envelope moves inward in mass, penetrating the hydrogen-exhausted regions. This is known as third dredge-up. As convection moves inward, nuclear processed materials are carried to the surface.

→ third; → dredge-up.

1) A declaration of an intention or determination to inflict punishment, injury, etc., in retaliation for, or conditionally upon, some action or course; menace.
2) An indication or warning of probable trouble (Dictionary.com).

M.E. threte, O.E. threat "pressure, oppression;" cognate with O.N. thraut "hardship, bitter end," Du. verdreiten, Ger. verdrießen "to vex," L. trudere "to press, thrust."

Harš, from Kurd. haraša "threat," haraša kirdan "threaten," related to Mid/Mod.Pers. rašk "envy, jealousy;" Lori, Laki erešt "assault, attack;" Tabari ârâšt "curse, anathema;" Av. arš- "to be envious;" Skt. īrs- "to be envious, envy;" Arm. her "anger, quarrel;" O.E. eorsian "to be malicious;" Proto-Ir. Harš- "to be envious."

1) To utter a threat against; menace.
2) To be a menace or source of danger to (Dictionary.com).

From M.E. thretnen, from O.E. thrêatnian, → threat

Infinitive from harš, → threat.

A cardinal number, 2 plus 1.

M.E.; O.E. threo, thrib, feminin and neuter of thri(e); cf. O.Fris. thre, M.Du., Du. drie, O.H.G. dri, Ger. drei, Dan. tre), cognate with Pers. sé, as below.

Sé, from Mid.Pers. sé; Av. θrayô, θrayas, tisrô, θri; cf. Skt. tráya, tri, trini; Gk. treis, L. tres, Lith. trys, O.C.S. trye, Ir., Welsh tri, O.E. threo, as above; PIE base *trei-.

The mathematical problem of studying the positions and velocities of three mutually attracting bodies (such as the Sun, Earth and Moon) and the stability of their motion. This problem is surprisingly difficult to solve, even in the simple case, called → restricted three-body problem, where one of the masses is taken to be negligibly small so that the problem simplifies to finding the behavior of the mass-less body in the combined gravitational field of the other two. See also → two-body problem, → n-body problem.

→ three; → body; → problem.

A flow whose parameters (velocity, pressure, and so on) vary in all three coordinate directions. Considerable simplification in analysis may often be achieved, however, by selecting the coordinate directions so that appreciable variation of the parameters occurs in only two directions, or even only one (B. Massey, Mechanics of Fluids, Taylor & Francis, 2006).

→ three; → dimensional; → flow.

The level that must be reached for a physical effect to begin or be noticeable.

M.E. threschold, O.E. threscold, threscwald "doorsill, point of entering."

Âstâné "threshold; a place of rest or sleeping," variant âstân; Mid.Pers. âstânak; ultimately from Proto-Iranian *ā-stānaka-, from *stā- "to stand;" cf. O.Pers./Av. sta- "to stand, stand still; set;" Av. hištaiti; Mid.Pers. êstâtan "to stand;" Mod.Pers. istâdan "to stand;" cf. Skt. sthâ- "to stand;" Gk. histemi "put, place, weigh," stasis "a standing still;" L. stare "to stand;" Lith. statau "place;" Goth. standan; PIE base *sta- "to stand."

The minimum energy necessary for the occurrence of some chemical/physical effect.

→ threshold; → energy.

The minimum energy, for an incident particle or photon, below which a particular reaction does not occur.

→ threshold; → reaction.

The minimum intensity of a signal that can be detected and recognized.

→ threshold; → signal.

A process in which two stars remain → bound after their → close encounter, leading to the formation of a → binary system. Tidal capture becomes possible when two stars pass each other so closely (within a few stellar radii) that their → tidal forces are able to absorb the excess energy of → unbound → orbital motion. The process was originally suggested by Fabian et al. (1975) to explain the origin of → low-mass X-ray binary systems observed for the first time in → globular clusters.

→ tidal; → capture.