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

An assembly of elements which are capable of functioning together to transmit power or signals.

→ transmission; → system.

The act or process of transmuting.
Physics: Any process in which a nuclide is transformed into a different nuclide, usually one of a different element.

Verbal noun of → transmute.

Of or pertaining to the speed of a body in a surrounding fluid when the relative speed of the fluid is → subsonic in some places and → supersonic in others.

→ trans-; → sonic.

Flow of a fluid over a body with a speed in the range just above and below the → Mach number 1.

→ transonic; → flow.

An emitter-receiver device that automatically responds upon reception of a designated incoming radar, radio or sonar signal

From trans(mitter), → trans-, + (res)ponder, → responder.

Math.: A permutation of a set of elements that interchanges two elements and leaves the remaining elements in their original positions. For example, the swapping of 2 and 5 to take the list 123456 to 153426 is a transposition.
Optics: The changing of the relative curves of a lens without changing its refractive value.

→ trans-; → position.

In medieval astronomy, a spurious oscillatory motion of the equinoxes thought to have a period of 7,000 years. This concept, attributed to Thâbit ibn Qurra (c. 830-901), had a profound influence on medieval astronomy. In order to explain trepidation, Thâbit was said to have added a new sphere to the eight Ptolemaic spheres beyond the sphere of fixed stars.

From L. trepidationem "agitation, trembling," from trepidare "to tremble, hurry," from trepidus "anxious, scared;" cf. Skt. trprá- "hasty;" PIE base *trep- "to shake, tremble."

Larzeš, verbal noun of larzidan "to tremble, shiver;" Mid.Pers. larzidan "to shake, tremble;" Manichean Mid.Pers. rarz- "to shiver with fever;" Proto-Iranian *rarz- "to shake, tremble."

In surveying and navigation, the process of deriving the linear distance between any two remote points by the division of a large area into adjacent triangles and using trigonometric relationships. See also → trilateration.

From M.L. triangulation-, from triangulare "to make triangles," → triangle.

Seguš-bandi, from sé, → three, + guš/gušé, → angle, + bandi verbal noun from bastan "to form, bind, tie" (Mid.Pers. bastan/vastan "to bind, shut;" Av./O.Pers. band- "to bind, fetter," banda- "band, tie;" cf. Skt. bandh- "to bind, tie, fasten;" Ger. binden; E. bind; PIE base *bhendh- "to bind").

The hydrogen molecule composed of three atoms in which one of the atoms is ionized. The molecular ion H₃⁺ plays a key role in the chemistry of gaseous → interstellar medium. It reacts efficiently with almost any neutral atom or molecule to initiate a network of ion-neutral reactions. It is responsible for producing molecules such as OH, CO, and H₂O. The first detection of H₃⁺ in the interstellar medium, via two closely spaced absorption lines (doublet) near 3.668 μm, were reported in two dense → molecular cloud cores along the lines of sight to the embedded → young stellar objects W33A and GL2136 (Geballe & Oka 1996). Since then H₃⁺ has been detected in several molecular clouds. It is believed that H₃⁺ forms via → cosmic ray → ionization of H₂ producing H₂⁺, which quickly reacts to another H₂ molecule to form H₃⁺ ( H₂ + CR → H₂⁺ and H₂⁺ + H₂→ H₃⁺ + H + 1.7 eV).

Tri-, → three; → atomic; → hydrogen; → molecular; → ion.

The formation of second-generation stars in a → molecular cloud, as set off by the action of → massive stars. → sequential star formation; → radiation-driven implosion.

→ trigger; → star formation.

Relating to or used in → trigonometry. → trigonometric function.

→ trigonometry; → -ic.

A function of an angle, one of six functions (sine, cosine, tangent, cotangent, secant, and cosecant) that represent ratios of sides of right triangles. Also called circular function.

→ trigonometric; → function.

The → parallax of a nearby star (less than 300 → light-years) against the background of more distant stars resulting from the motion of the Earth in its orbit around the Sun.

→ trigonometric; → parallax.

The branch of mathematics dealing with the relations of the sides and angles of triangles; also the various algebraic functions of these relations.

From N.L. trigonometria, from Gk. trigonon "triangle" (from tri-, → three, + gonia "angle," cognate with Pers. zânu "knee") + metron, → -metry.

Sebarsanji, from sebar, → trianle, + -sanji, → -metry.

A geometrical method in land surveying for the determination of the relative position of points. In contrast to → triangulation, trilateration involves measuring the lengths of the three sides of touching or overlapping triangles and not their angles.

→ tri-; → lateral; → side; → -tion.

A compound → vowel sound resulting from the succession of three simple vowels pronounced in a single syllable (as in power, hour, fire).

Tri-, → three; → diphthong.

A rare event involving a particularly intricate set of movements of two planets or a planet and a star where they meet each other three times in a short period either in opposition or at the time of inferior conjunction, if an inferior planet is involved. The visible movement of the planet or the planets in the sky is therefore normally prograde at the first conjunction, retrograde at the second conjunction and again prograde at the third conjunction.

→ triple; → conjunction.

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.

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.

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.