An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



<< < -ti tan Tay tem ten Ter the the the the thi thr tid tim Tit top tot tra tra tra tra tri Tri tru Tuc tur Tyc Typ > >>

Number of Results: 544
turnoff star
  ستاره‌ی ِ رهگشت   
setâre-ye rahgašt

Fr.: étoile du tournant final de la séquence principale   

A star that has ended → hydrogen burning in its core but is still burning hydrogen in a shell that surrounds the core, just before evolving into a → red giant.

turnoff; → star.

firuzé (#)

Fr.: turquoise   

A greenish blue mineral consisting of aluminium phosphate colored by traces of copper.

From M.Fr. turquoise (M.E. turkeis), from O.Fr. turqueise "Turkish," because it was first brought to Europe from Turkestan. The gem does not occur in Turkey.

Mid.Pers. pirôzak, pirôcak, cf. Skt. peraja, peroja.

Tusi couple
  جفت ِ توسی، ~ ِ طوسی   
joft-e Tusi (#)

Fr.: couple de Tusi   

Nasireddin couple.

Named for Nasireddin Tusi (1201-1274), director of Marâgha observatory who created the Ilkhani zij; → couple.

Tusi's staff
  چوبدست ِ توسی   
cubdast-e Tusi

Fr.: bâton de Tusi   

Sharafeddin's staff.

Named after the Iranian mathematician and astronomer Sharafeddin Tusi (c1135-1213), who invented the instrument. Not to be confused with Nasireddin Tusi (1201-1274), → Nasireddin couple.


Fr.: tuteur   

1) A teacher who instructs students without institutional connection.
2) A teacher of a rank below instructor in some US universities.

From tutor, M.E., from O.Fr. tutour "guardian, private teacher," from L. tutor "protector, watcher," from tutus, variant p.p. of tueri "to watch over," of unknown origin.

Âmuxtâr, literally "teacher," from âmuxtan, → teach, + -âr agent noun suffix (such as xaridâr).


Fr.: tutoriel   

1) A series of intensive lessons given to an individual student or to a small group of students.
2) Programmed instructions about running a particular → software package and often built into that package.

tutor + → -al.

Âmuxtâl, from âmuxtan, → teach, + → -al.

TW Hydrae
   TW هودرا   
TW Hudrâ

Fr.: TW Hydrae   

The nearest known → classical T Tauri star, situated some 56 → parsecs away in the constellation → Hydra, far from any → molecular cloud (abbreviated TW Hya). It is a variable star with large Hα-emission → equivalent width. TW Hya is similar in mass to the Sun, but is only about 8 million years old. The star appears to be → accreting from a remarkable → face-onprotoplanetary disk of dust and gas, resolved in images from the → Hubble Space Telescope. Stellar light scattered from the optically thick dust disk is seen from 20 to 230 AU. The → scattering profile indicates that the disk is → flared, not geometrically flat. TW Hya is accompanied by a group of other low-mass stars with similar ages and space motions, comprising the → TW Hydrae association. An → exoplanet of mass nearly 10 → Jupiters has been detected around TW Hya. It orbits the star with a period of 3.56 days at 0.04 AU, inside the inner rim of the disk.


TW Hydrae association
  آهزش ِ TW هودرا   
âhazeš-e TW Hudrâ

Fr.: Association TW Hydrae   

A young (≤ 100 million years) association of stars (abbreviated TWA) with at least 27 members, from → intermediate mass stars to planetary mass objects. Five of them, including → TW Hydrae, display signatures of → T Tauri stars. TWA is the first moving group of young nearby (≤ 100 → paesecs) stars to be identified.

TW Hydrae; → association.

bist (#)

Fr.: vingt   

A cardinal number, 10 times 2.

M.E.; O.E. twentig "group of twenty," from twegentwo; cf. O.Fris. twintich, Du. twintig, O.H.G. zweinzug, Ger. zwanzig.

Bist "twenty;" Mid.Pers. wist "twenty;" Av. vīsaiti "twenty;" cf. Skt. vimśati- "twenty;" Gk. eikosi "twenty;" L. uiginti "twenty."

dobâr (#)

Fr.: deux fois   

Two times, as in succession; on two occasions.

M.E. twies, from O.E. twiga, twigea "two times," from twi-, → two; cf. L. bis, Gk. dis, Skt. dvis, Av. biš.

Dobâr, from do, → two, + bâr "time, fold," from Mid.Pers. bâr; Proto-Ir. *uara-; cf. Av. var- "to choose; to convince;" Skt. vāra- "time, turn."

nimtâb (#)

Fr.: crépuscule   

The diffused light from the sky when the Sun is below the → horizon, either from daybreak to → sunrise or, more commonly, from → sunset to nightfall. There are three types of twilight: → astronomical twilight, → civil twilight, and → nautical twilight. They are divided on the basis of the → solar depression angle.

M.E., cognate with Du. tweelicht, Ger. zwielicht, from twi- a combining form meaning "two, twice," but it appears to refer to "half" light, rather than the fact that twilight occurs twice a day + → light.

Nimtâb, from nim, nimé, → half, + tâb "light," present stem of tâbidan "to shine," → luminosity.

cešmak (#)

Fr.: scintillation   

A shining with intermittent light, as the twinkling of the stars. → scintillation.

M.E. twinklen (v.), O.E. twinclian, frequentative of twincan "to wink, blink;" related to M.H.G. zwinken, Ger. zwinkern.

Cešmak "twinke," from cešm, → eye, + -ak relation suffix.

twins paradox
  پارادخش ِ همزادها   
pârâdaxš-e hamzâdhâ

Fr.: paradoxe des jumeaux   

A thought experiment in special relativity, according to which if one of a pair of twins (A) remains on Earth, and the other (B) travels at a speed near the speed of light, B will be younger than A upon returning to Earth. In fact there is no paradox, because the two perspectives, A and B's, are actually not completely symmetric. There is no fixed time difference between the events, and different observers experience different intervals of time between the same two events. In fact, B returns younger than A because only B travels in a non-inertial (accelerating) reference frame. From A's point of view, B experiences time dilation, but from B's point of view the distance traveled is shortened because of length contraction. If B leaves in the year 2000 and returns in 2020, for A 20 years have elapsed. For B it depends on his travel speed. If has has moved as fast as 86% of the speed of light for him 10 years have passed. If his speed has been 99.5% of the speed of light the travel duration for him has been 2 years. This effect has been verified experimentally by measurements with atomic clocks.

Twin M.E.; O.E. twinn; cf. O.N. tvinnr, O.Dan. tvinling, Du. tweeling, Ger. zwillung; → paradox.

Pârâdaxš, → paradox; hamzâdhâ, plural of hamzâd "twin," literally "born together," from ham- "together" → syn- + zâd "born," from zâdan "to bring forth, give birth" (Mid.Pers. zâtan; Av. zan- "to bear, give birth to a child, be born," infinitive zazāite, zāta- "born;" cf. Skt. janati "begets, bears," janitár "progenitor, father;" Gk. genetor "progenitor;" L. gignere "to beget," nasci "to be born," as above, PIE base *gen- "to give birth, beget").

do (#)

Fr.: deux   

A cardinal number, 1 plus 1. → two-color diagram; → two-photon emission.

M.E., from O.E. twa, feminine and neuter form of twegen "two," from P.Gmc. *twai (cf. O.S., O.Fris. twene, twa, O.N. tveir tvau, Du. twee, O.H.G. zwene, zwo, Ger. zwei, Goth. twai), cognate with Pers. do, as below.

Do "two," from Mid.Pers. do; Av. dva-; cf. Skt. dvi-; Gk. duo; L. duo (Fr. deux), di; Lith. dvi; O.C.S. duva; PIE base *duwo.

Two Micron All Sky Survey (2MASS)

Fr.: 2MASS   

An astronomical → survey conducted from 1997 to 2001 of the entire sky in near-infrared J, H, and K bands (wavelengths 1.25, 1.65, and 2.17 microns respectively). The aim was to detect and characterize point sources brighter than about 1 → mJy in each band, with → signal-to-noise ratio greater than 10, using a pixel size of 2".0. Two automated 1.3-m telescopes were used, one at Mt. Hopkins, AZ, and one at CTIO, Chile. 2MASS is currently producing the following data products: 1) A digital atlas of the sky comprising approximately 4 million 8' × 16' images, having about 4" spatial resolution in each of the wavelength bands. 2) A point source catalog containing accurate positions and fluxes for 300 million stars and other unresolved objects. 3) An extended source catalog containing positions and total magnitudes for more than 1,000,000 galaxies and nebulae.

two; → micron; → all-sky survey.

two-body problem
  پراسه‌ی ِ دو جسم   
parâse-ye do jesm

Fr.: problème à deux corps   

In classical mechanics, the study concerned with the dynamics of an isolated system of two particles subject only to the Newtonian gravitational force between them. The problem can be separated into two single-particle problems with the following solutions. The equation of the → center of mass is governed by the equation of the same form as that for a single particle. Moreover, the motion of either particle, with respect to the other as origin, is the same as the motion with respect to a fixed origin of a single particle of → reduced mass acted on by the same internal force. See also → three-body problem, → n-body problem.

two; → body; → problem.

two-color diagram
  نمودار ِ دو رنگ   
nemudâr-e do rang

Fr.: diagramme deux couleurs   

A graph on which two color indices such as B-V and U-B are plotted, one along each axis, for a sample of stars or other objects, such as stars.

two; → color; → diagram.

two-dimensional flow
  تچان ِ دو-وامونی   
tacân-e do-vâmuni

Fr.: écoulement bi-dimensionnel   

A flow whose parameters are functions of time and two space coordinates (x and y) only. There is no variation in the z direction and therefore the same → streamline pattern could at any instant be found in all planes in the fluid perpendicular to the z direction (B. Massey, Mechanics of Fluids, Taylor & Francis, 2006).

two; → dimensional; → flow.

two-photon emission
  گسیل ِ دو-فوتونی   
gosil-e do-fotoni

Fr.: émission à deux photons   

The simultaneous emission of two photons whose sum of energies is equal to that of a single electron transition. The energy of each individual photon of the pair is not fixed, so that the spectrum of two-photon emission is continuous from the wavelength of that transition to infinity. In practice, there is a peak in wavelength distribution of the emitted photons. Two-photon emission is studied atomic physics with application in astrophysics, as it contributes to the continuum radiation from → planetary nebulae. It was recently observed in condensed matter and specifically in → semiconductors.

two; → photon; → emission.


Fr.: TY CrA   

A multiple stellar system embedded in a → reflection nebula (NGC 6726/6727) in the → Corona Australis star forming region. The three stars are within 1.5 → astronomical units of each other and lie at a distance of 129 pc. Two of its components form a → double-line eclipsing binary with an orbital period of almost 3 days. The primary is a → main sequence star (mass 3.16 solar masses, effective temperature 12,000 K) and the secondary a → pre-main sequence star (mass 1.64 solar masses, effective temperature 4,900 K) with an age of a few million years. A third spectroscopic component is in a wide orbit around the eclipsing pair. A fourth star is located at a projected distance of about 0.3 arcsecond (40 AU) from the compact tertiary system.

Corona Australis.

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