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
turbulent Jeans mass
  جرم ِ جینز ِ آشوبناک   
jerm-e Jeans-e âšubnâk

Fr.: masse de Jeans turbulente   

The characteristic mass for → cloud fragmentation in a → turbulent medium. While the standard → Jeans mass depends simply on the gas mean → density and → temperature, and fragmentation is purely gravitational, turbulent Jeans mass depends strongly also on the → Mach number (Chabrier et al. 2014, arXiv:1409.8466).

turbulent; → Jeans; → mass.

turbulent plasma
  پلاسمای ِ آشوبناک   
plasmâ-ye âšubnâk

Fr.: plasma turbulent   

A plasma characterized by a → turbulent flow regime.

turbulent; → plasma.

  ۱) گردیدن، گشتن؛ گرداندن؛ ۲) گشت   
1) gardidan, gaštan; gardândan; 2) gašt

Fr.: 1) tourner; faire tourner; 2) tour, tournure   

1) To move, or cause to move, around, or partly around a center.
2) The action or an act of turning about a center or axis.

M.E. turnen; O.E. turnian "to rotate, revolve," also from O.Fr. torner "to turn," both from L. tornare "to turn on a lathe," from tornus "lathe," from Gk. tornos "lathe, tool for drawing circles."

Gardidan "to turn; turning," variant gaštan "to turn, to change;" Mid.Pers. vartitan; Av. varət- "to turn, revolve;" Skt. vrt- "to turn, roll," vartate "it turns round, rolls;" L. vertere "to turn;" O.H.G. werden "to become;" PIE base *wer- " to turn, bend."

turning point
gaštgâh (#)

Fr.: tournant   

The closest point in the path of a sound wave to the center of a star, as studied in → asteroseismology. Starting from the surface, the sound wave first moves into the star almost straight toward the center. Its path then deflects, because of the increasing → sound speed, so that it misses the center of the star. After the turning point, the wave moves out again until it reaches the surface, where it is reflected. If exactly an integer number of wavelengths fits between two reflections at the surface, the sound wave corresponds to a → standing wave with a specific pattern of → node lines on the surface.

turn; → point.


Fr.: tournant   

1) A small road that branches off from a larger one, or a place where one diverges from a former course.
2) An act of turning off.

turn; → off.

Rahgašt, from rah, variant râh "path, way," → Milky Way, + gašt, → turn.

turnoff point
  نقطه‌ی ِ رهگشت   
noqte-ye rahgašt

Fr.: tournant final de la séquence principale   

Same as → main-sequence turnoff.

turnoff; → point.

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.

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