An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 551
tensor density
  چگالی ِ تانسور   
cagâli-ye tânsor

Fr.: densité de tenseur   

A generalization of the tensor concept that like a tensor transforms, except for the appearance of an extra factor, which is the → Jacobian matrix of the transformation of the coordinates, raised to some power, in transformation law. The exponent, which is a positive or negative integer, is called the weight of the tensor density. → weight of a tensor density. Ordinary tensors are tensor densities of weight 0. Tensor density is also called → relative tensor.

tensor; → density.

tensor field
  میدان ِ تانسوری   
meydân-e tânsori

Fr.: champ tensoriel   

A field of space and time each point of which has multiple directionality, and is describable by a tensor function.

tensor; → field.

tensor perturbation
  پرتورش ِ تانسوری   
partureš-e tânsori

Fr.: perturbation tensorielle   

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.

tensor rank
  رتبه‌ی ِ تانسور   
rotbe-ye tânsor

Fr.: rang de tenseur   

The total number of → contravariant and → covariant indices (→ index) of a → tensor.

tensor; → rank.

tensor-vector-scalar (TeVeS) theory


A theory put forward to provide a basis for a relativistic generalization of the → MOdified Newtonian Dynamics (MOND) paradigm. TeVeS is based on three dynamical fields: a tensor field, a vector field, and a scalar field. In contrast to general relativity, it has two metrics, an Einstein metric and a physical metric. TeVeS has attracted considerable attention, since it can explain many galactic and cosmological observations without the need for → dark matter. Proposed by J. D. Bekenstein, 2004, "Relativistic gravitation theory for the modified Newtonian dynamics paradigm", Phys. Rev. D, 70, 083509, arXiv:astro-ph/0403694.

tensor; → vector; → scalar; → theory.


Fr.: éjecta   

A general term for materials of all types and sizes that are ejected by volcanic eruptions. It includes particles as tiny as volcanic ash and as large as bombs and blocks.

From Gk. tephra "ashes."

tera- (T)
terâ- (#)

Fr.: tera-   

Prefix denoting one million million (1012).

From Gk. teras "monster."

terbiom (#)

Fr.: terbium   

A metallic chemical element; symbol Tb. Atomic number 65; atomic weight 158.9254; melting point 1,356°C; boiling point 3,123°C; specific gravity about 8.25. Terbium was discovered by the Swedish surgeon and chemist Carl-Gustav Mosander in 1843 in an yttrium salt, which he resolved into three elements. He called one yttrium, a rose colored salt he called terbium and a deep yellow peroxide he called erbium.

From the "village of Ytterby" in Sweden, where the mineral ytterbite (the source of terbium) was first found.


Fr.: terme   

1) A word or group of words that has a precise meaning and expresses a definite idea, used in a particular science, art, or profession. See also → terminology; → determine.
2) Math.: In an expression, a number or a letter standing alone; or a combination of such representing a unit, e.g.: a, b, 5, 4ab, 3a/b.
3) Physics: A set of atomic states having a definite → configuration and → spin and → orbital angular momentum  → quantum numbers. In the → LS coupling scheme, the entity 2S+1LJ, in which 2S+1 is called the → multiplicity of the term.
4) Logic: The → subject or → predicate of a → categorical proposition. See also → syllogism.
5) In → first-order logic, an → individual constant, → individual variable, or → function.

M.E. terme, from O.Fr., from L. terminus "boundary, limit, end; boundary stone or marker," variant termen "boundary, end;" cognate with Gk. termon "limit, boundary;" Skt. tarman "the top of the sacrificial (usually tripod) post; passage;" Irish tearmann "a refuge, sanctuary, asylum;" this Irish word would point to the sacredness of the sacrificial post in primitive IE customs; Hittite tarma- "peg, plug, nail;" PIE base *ter- "to cross;" cf. Pers. tarm, târem, tarâ-, Av. tar- "to cross over," as below.

Tarm, variant târem "boundary, limit," more specifically "a wooden palisade to exclude people from a garden," also "a wooden building of a circular form with an arched roof" (cf. Irish tearmann, as above), Tabari talm "pole, stick" (that marks a boundary), Tâleši/Tâti talmi "pole, stick," Garkâni taram "lever," Lori, Laki tarm "poles fastened together in order to carry a corpse to the village cemetery;" O.Pers./Av. tar- "to cross over," O.Pers. vi-tar- "to go across," Mid.Pers. vitartan "to pass," Mod.Pers. gozar, gozaštan "to pass, cross;" cf. Skt. tarman "the top of the sacrificial post; passage," tar- "to pass (through), overcome," tárati "crosses, passes," tirás "through, across, beyond;" see also → trans-.

  ۱) پایانی؛ ۲) پایانه   
1) pâyâni; 2) pâyâné

Fr.: terminal   

1) Forming or found at the extreme point or limit of something, or relating to the very end of something.
2) Computers: An input/output device having a keyboard for communicating with a computer and usually a display.

M.E., from L. terminalis "pertaining to a boundary or end, final," from terminus "end, boundary line," → term.

Pâyâni, pâyâné, noun and adj. from pâyân "end, extremity; limit, boundary," from pâ(y) "foot; step" (Mid.Pers. pâd, pây; Av. pad- "foot;" cf. Skt. pat; Gk. pos, genitive podos; L. pes, genitive pedis; P.Gmc. *fot; E. foot; Ger. Fuss; Fr. pied; PIE *pod-/*ped-).

terminal age main sequence (TAMS)
  رشته‌ی ِ فریست با سن ِ پایانی   
rešte-ye farist bâ senn-e pâyâni

Fr.: séquence principale d'âge terminal   

The locus of stars on the → Hertzsprung-Russell diagram that are at the point of exhausting hydrogen in their cores. TAMS forms the upper luminosity boundary of the → main sequence strip. See also → zero age main sequence (ZAMS).

terminal; → age; → main; → sequence.

terminal velocity
  تندای ِ پایانی   
tondâ-ye pâyâni

Fr.: vitesse terminale   

1) The constant maximum velocity reached by a body falling under gravity through a liquid or gas, especially the atmosphere. The body ceases to accelerate downward because the force of gravity is equal to the opposing force of resistance by the medium.
2) The velocity acquired at the end of a body's motion.
3) The velocity attained by → stellar wind at very large distance from the star. The material that escapes from the outer layers of the stars is accelerated outward from a small radial velocity at the → photosphere of the star, to some high velocity at large distance from the star. The theory of → radiation-driven winds predicts that the terminal velocity scales with the → escape velocity as: v  ≅ 2-3 vesc. The winds of hot → O stars experience fast acceleration and reach 80% of their terminal velocity near the star (some 3 R*). The terminal velocity ranges from about 10 km s-1 for a cool → supergiant star to 3000 km s-1 for a luminous hot star. Terminal velocities are quite accurately measured from the violet trough of saturated → P Cygni line profiles in the ultraviolet (mainly N V λ1239, C IV λ1548, Si IV λ1394).

terminal; → velocity.

termination shock
  تش ِ پایانی، شوک ِ ~   
toš-e pâyâni, šok-e ~

Fr.: choc terminal   

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.


Fr.: terminateur   

The dividing line between the illuminated and the un-illuminated part of the Moon's or a planet's disk.

From L. terminator, from terminare, from terminusterm.

Šid-marz, literally "light boundary," from šid "light, sunlight" (Mid.Pers. šêt "shining, radiant, bright;" Av. xšaēta- "shining, brilliant, splendid, excellent") + marz "boundary, limit" (Mid.Pers. marz "boundary;" Av. marəza- "border, district," marəz- "to rub, wipe;" Mod.Pers. parmâs "contact, touching" (→ contact), mâl-, mâlidan "to rub;" PIE base *merg- "boundary, border;" cf. L. margo "edge" (Fr. marge "margin"); P.Gmc. *marko; Ger. Mark; E. mark, margin).


Fr.: terminologie   

1) The system of terms belonging to a particular science, art, specialized subject, or social group. Terminology is the way of naming concepts, which generally precede the corresponding terms. See also → lexicology.
2) The theory or science dealing with the relations between → terms and → concepts.

A hybrid word coined first in Fr., before 1764, by Yves Marie André (1675-1764), a Jesuit mathematician and philosopher, from termin, from L. terminus, → term, + epenthetic vowel -o- + Gk. -logia, → -logy. Recoined or borrowed in Ger. Terminologie in 1786, by C.G. Schütz of Jena; first appeared in E. in 1801.

From tarm, → term, + -šenâsi, → -logy.


Fr.: terraformer   

To alter the environment of a planet or moon in a → terraforming process in order to make it habitable for life forms.

Probably taken from noun terraform, from L. terra "earth," → terrestrial; → form.

From zamin, → earth, + disidan "to → form."


Fr.: terraformation   

The hypothetical process of altering the environment (atmosphere, temperature, surface topography, or ecology) of another planet or moon to improve the chances of survival of an indigenous biology or to allow habitation by terrestrial life forms. See also → ecopoiesis.

Verbal noun of → terraform. The term first appeared in a science fiction novel, Seetee Shock (1949) by Jack Williamson, an American science fiction writer; but the actual concept pre-dates this work.

zamini (#)

Fr.: terrestre   

Pertaining to, consisting of, or representing the Earth as distinct from other planets.

From L. terrestris "earthly," from terra "earth," literally "dry land" (as opposed to "sea"); from PIE base *ters- "to dry" (cf. Pers. tešné "thirsty;" Mid.Pers. tašnak "thirsty;" Av. taršu- "dry," taršna- "thirst;" Skt. trsta- "dry," tars- "to be thirsty;" Gk. teresesthai "to become or be dry," L. torrere "to dry up, roast," Goth. þaursus "dry, barren," O.H.G. derren "to make dry," durst "thirst;" Ger. dürr "arid;" O.E. þurstig "thirsty").

Zamini adj. of zamin, variant zami "earth, floor, land;" Mid.Pers. zamig; Av. zam- "the earth;" cf. Skt. ksam- "the ground, earth;" Gk. khthôn, khamai "on the ground;" L. homo "earthly being" (as in homo sapiens, homicide, humble, humus, exhume), humus "the earth;" O.Russ. zemi "land, earth;" PIE root *dh(e)ghom "earth".

Terrestrial Dynamical Time
  زمان ِ توانیک ِ زمینی   
zamân-e tavânik-e zamini

Fr.: temps dynamique terrestre   

A uniform atomic time scale for apparent geocentric ephemerides defined by a 1979 IAU resolution, which replaced Ephemeris Time. TDT is independent of the variable rotation of the Earth, and the length of the tropical year is defined in days of 86,400 seconds of international atomic time. In 1991 it was replaced by Terrestrial Time.

terrestrial; → dynamical; → time.

terrestrial gravitational constant
  پایای ِ گرانشی زمینی   
pâyâ-ye gerâneši-ye zamini

Fr.: constante gravitationnelle terrestre   

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.

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