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
Triton (#)

Fr.: Triton   

The seventh and the largest of → Neptune's satellites. It has a diameter of 2,700 km and orbits its planet at a mean distance of 354,760 km every 5.877 days. Triton was discovered by William Lassell in 1846 scarcely a month after Neptune was discovered. Triton is colder than any other measured object in the solar system with a surface temperature of -235° C. It has an extremely thin atmosphere. Nitrogen ice particles might form thin clouds a few kilometers above the surface. The atmospheric pressure at Triton's surface is about 15 microbars, 0.000015 times the sea-level surface pressure on Earth. Triton is the only large satellite in the solar system to circle a planet in a → retrograde motion, that is in a direction opposite to the rotation of the planet.

In Gk. mythology, Triton is a god of the sea, the son of Poseidon (Neptune); usually portrayed as having the head and trunk of a man and the tail of a fish.


Fr.: trivial   

1) Of very little importance or value; insignificant; commonplace; ordinary.
2a) Math.: A solution of an equation in which the value of every variable of the equation is equal to zero. For example, x2 + 2y2 = x + 3y has a trivial solution x = 0, y = 0.
2b) Of a theorem or proof: simple, transparent, or immediately evident.
Any theorem once a proof has been obtained, no matter how difficult the theorem was to prove in the beginning.
2c) For any natural number, the number itself and 1 which are called trivial divisors.
3) Chemistry: → trivial name.

From M.L. trivialis "found everywhere, commonplace; known by every body," from trivium literally "crossroad, a place where three roads meet," also "the lower division of the seven liberal arts taught in medieval universities, i.e. grammar, rhetoric, and logic," from tri-, → three, + via "road," since it was common in Roman Empire for three roads to meet.

Zab "easy, unbought, gratis; straight," variant zap, related to sabok "light, not heavy; unsteady;" Proto-Iranian *θrap-/tarp- "to be unsteady;" cf. Kurd. terpin "to stumble;" Pashto drabəl "to shake, press down;" Skt. trepa- "hasty;" Gk. trepein "to turn;" L. trepidus "agitated, anxious;" PIE *trep- "to shake, tremble."

trivial name
  نام ِ زب   
nâm-e zab

Fr.: nom trivial   

Chemistry: A common name for a chemical compound derived from the natural source, or of historic origin, and not according to the systematic nomenclature. For example, the trivial name of sodium chloride is → salt.

trivial; → name.


Fr.: trivialité   

The quality or state of being → trivial; something trivial.

trivial; → -ity;.

  زبیدن، زب‌کردن   
zabidan, zab kardan

Fr.: trivialiser   

To make → trivial.

trivial; → -ize

Trojan asteroid
  سیارک ِ ترویایی   
sayyârak-e Troâ-yi

Fr.: astéroïde troyen   

A member of the family of asteroids that share → Jupiter's orbit and lie in elongated, curved regions around the two → Lagrangian points 60° ahead and behind of Jupiter. The Lagrangian points L4 and L5 host several thousands of them. Originally, the term Trojan applied only to asteroids sharing Jupiter's orbit; however, planetoidal bodies have been discovered at the Lagrangian points of Mars and Neptune as well, and are also referred to as → Mars Trojans and Neptune Trojans respectively.

M.E.; O.E. Troian, from Trojanus, from Troj(a) "Troy" + -anus; → asteroid.

Sayyârakhâ plural of sayyârak, → asteroid; Troâ-yi adj. of Troâ "Troy."


Fr.: tropique   

Either of the two parallels of latitude on Earth at which the Sun appears overhead at the → summer and → winter solstices each year: → Tropic of Cancer, → Tropic of Capricorn . The tropics lie at latitudes 23°26', north and south, an angle defined by the Earth's → axial inclination.

M.E., from L. tropicus, from Gk. tropikos "of or pertaining to a turn or change; of or pertaining to to the turn of the Sun's apparent motion at solstice," from trope "a turning."

Hurgard, literally "Sun's turning," from hur, → Sun, + gard "turning, changing," from gardidan "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."

Tropic of Cancer
  هورگرد ِ خرچنگ   
Hurgard-e Xarcang

Fr.: Tropique du Cancer   

A parallel of latitude on the Earth, 23°26' north of the equator, where the Sun is directly overhead on the northern → summer solstice (around the 21st June each year), because the Sun reaches its most northerly declination. Some 3,000 years ago, this occurred when the Sun was in the → Zodiac constellation → Cancer, hence the name. However, → precession has resulted in a shift of the position of the Sun so that it is now in the constellation → Gemini on the summer solstice.

tropic; → Cancer.

Tropic of Capricorn
  هورگرد ِ وهیگ   
Hurgard-e Vahig

Fr.: Tropique du Capricorne   

A parallel of latitude on the Earth, 23°26' south of the equator, where the Sun is directly overhead on the southern → summer solstice (around the 21st December each year), because the Sun reaches its most southerly declination. Some 3,000 years ago, this occurred when Sun was in the → Zodiac constellation → Cancer, hence the name. However, → precession has resulted in a shift of the position of the Sun so that it is now in the constellation → Sagittarius on the northern → winter solstice.

tropic; → Capricorn.


Fr.: tropique   

1) Geography: Pertaining to, characteristic of, occurring in, or inhabiting the → tropics.
2) Astro.: A misnomer for → solar, as in → tropical year, or → vernal equinox, as in → tropical month.

tropic + → -al.

tropical month
  ماه ِ هموگانی   
mâh-e hamugâni

Fr.: mois tropique   

The average period of the revolution of the Moon about the Earth with respect to the → vernal equinox, a period of 27.321 582 days (27d 7h 43m 4.7s).

tropical; → month.

Mâh, → month; hamugâni, of or pertaining to hamugân, → equinox.

tropical year
  سال ِ هورگردی   
sâl-e hurgardi

Fr.: année tropique   

The interval during which the Sun's mean longitude, referred to the mean equinox of date, increases by 360 degrees. Its mean length for the epoch J2000.0 is 365.24217879 real solar days (approximately 365.2422 days). This concept of tropical year, adopted by the International Astronomical Union at its General Assembly in Dublin, September 1955, has often been confounded with the → vernal-equinox year. In fact the mean period between two successive true vernal equinoxes is different from the tropical year. This period, which is equal to 365.24236460 solar days (about 365.2424 days), is the real mean length of the year in the Iranian calendar. The difference between the two year lengths is due to the fact that the Earth's orbital velocity around the Sun is not uniform, since the orbit is an ellipse. At the perihelion of its orbit the Earth is closest to the Sun, and therefore moves faster than average, while at aphelion, when it is farthest away from the Sun, it moves slower. Therefore the interval between two successive vernal equinoxes is not the same as the period between two successive summer solstices. In fact the tropical year does not depend on a specific origin for the annual apparent motion of the Sun. For detailed discussion see: A concise review of the Iranian calendar.

tropical; → year.


Fr.: tropo-   

A combining form meaning "turn, change."

From Gk. tropos "turn," trope "a turning," from trepein "to turn;" cognate with Pers. sabok and zab, → trivial.

Gašt "turning," past stem of gaštan, gardidan "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").

gaštmarz (#)

Fr.: tropopause   

The boundary between the → troposphere and → stratosphere. Its height, varying with latitude and seasons, is from 8 km at poles, to 18 km at equator; it is higher during winter time. The atmospheric temperature decreases from ground upward until the tropopause. Then it increases in stratosphere because of the absorption of solar ultraviolet radiation.

tropo- + pause "break, cessation, stop," from M.Fr. pause, from L. pausa "a halt, stop, cessation," from Gk. pausis "stopping, ceasing," from pauein "to stop, to cause to cease."

From gašt, → tropo-, + marz "frontier, border, boundary" (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.: troposphère   

The lower part of the Earth's atmosphere in which temperature decreases with height, except for local areas of → temperature inversion.

tropo- + → sphere.

Trouton's rule
  رزن ِ تروتون   
razan-e Trouton

Fr.: règle de Trouton   

The ratio of the → molar heat of vaporization of any liquid to its → boiling point is a constant, about 88 joules per mole per Kelvin. The rule is equivalent to the statement that the → entropy of vaporization is constant. It is not always followed, especially by liquids such as water in which hydrogen bonding occurs between the molecules.

Named after Frederick Thomas Trouton (1863-1922), an Irish physicist; → rule.

Trouton-Noble experiment
  آزمایش ِ تروتون-نوبل   
âzmâyeš-e Trouton-Noble

Fr.: expérience de Trouton-Noble   

An experiment first carried out in 1903 to reveal the absolute motion of the Earth with respect to the → ether. The experiment consists of detecting a torque on a charged parallel-plate → capacitor that was suspended so that its plates were vertical. Since the Earth moves around the Sun, the moving charges were expected to produce magnetic fields, and the resulting torque should tend to turn the capacitor bringing its plates parallel to its velocity. No such effect was observed, and the absence of the torque supports the theory of → special relativity.

Named after Frederick T. Trouton (1863-1922) and Henry R. Noble; → experiment.

râstin (#)

Fr.: vrai   

Being in accordance with the actual state or conditions; e.g. → true anomaly; → true equinox; → true horizon; → true north; → true Sun.

M.E. trewe (adj. and adv.); O.E. triewe, treowe "trustworthy" (cf. O.Fris. triuwi, Du. getrouw, O.H.G. gatriuwu, Ger. treu, O.N. tryggr, Goth. triggws "faithful, trusty").

Râstin, from râst "right, true; just, upright, straight;" Mid.Pers. râst "true, straight, direct;" Soghdian rəšt "right;" O.Pers. rāsta- "straight, true," rās- "to be right, straight, true;" Av. rāz- "to direct, put in line, set," razan- "order;" cf. Skt. raj- "to direct, stretch," rjuyant- "walking straight;" Gk. orektos "stretched out;" L. regere "to lead straight, guide, rule," p.p. rectus "right, straight;" M.E.; O.E. reht, riht; cf. O.H.G. reht, Ger. recht, O.N. rettr, Goth. raihts; PIE base *reg- "move in a straight line," hence, "to direct, rule."

true anomaly
  ناسانی ِ راستین   
nâsâni-ye râstin

Fr.: anomalie vraie   

One of the standard → orbital elements, which is the angle measured at the → focus nearest the → periapsis of an elliptical orbit, between the periapsis and the → radius vector from the focus to the orbiting body.

true; → anomaly.

true celestial equator
  هموگار ِ آسمانی ِ راستین   
hamugâr-e âsmâni-ye râstin

Fr.: équateur céleste vrai   

The → celestial equator of date, which is the → great circle on the → celestial sphere perpendicular to the instantaneous axis of rotation of the Earth. Its interaction with the → ecliptic defines the → vernal equinox of date and the → autumnal equinox of date.

true; → celestial; → equator.

<< < -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 > >>