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

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.

In composition, having three nitro groups (NO₂), especially replacing hydrogen. → trinitrotoluene.

From L. tri-, a combining form meaning → three + nitro- a combining form used in the names of chemical compounds in which the nitro group is present.

A yellow, solid chemical compound, that does not occur naturally in the environment. More specifically, 2,4,6-trinitrotoluene (C₆H₂(NO₂)₃CH₃), is commonly known as TNT. It is an explosive extensively used in munitions and for demolitions.

→ trinitro- + → toluene.

1) A → polynomial that consists of three terms.
2) Of, pertaining to, or consisting of a trinomial.

→ tri- + nomial, short for → nomnial.

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.

Threefold; consisting of three parts. → triple alpha process; → triple conjunction; → triple point; → triple star.

M.E., from M.L. triplare "to triple," from L. triplus "threefold, triple," from tri-, → three, + -plus "-fold."

Setâyi, from setâ, from sé→ three + tâ "fold, plait, ply; piece, part," Mid.Pers. tâg "piece, part."

A chain of nuclear fusion reactions by which three helium nuclei (→ alpha particles) are transformed into → carbon. First two nuclei of helium collide, fuse, and form a nucleus of → beryllium: ⁴He + ⁴He ↔ ⁸Be, which is unstable and will decay back into two helium nuclei within a few 10^-17 seconds. However, due to sufficiently high density and temperature in the stellar core, during a third collision between beryllium and helium, carbon is formed: ⁸Be + ⁴He → ¹²C + γ. The triple-alpha process is possible owing to the existence of the → Hoyle state. It is the main source of energy production in → red giants and → red supergiants in which the core temperature has reached at least 100 million K. Also called → Salpeter process.

→ triple; → alpha particle; → process.

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 definite pressure and temperature at which all three phases of a substance coexist in → phase equilibrium. The triple point of water has a pressure of 4.58 mm of Hg and a temperature of 273.16 °K.

→ triple; → point.

Noqté, → triple; segâné, from sé→ three + -gâné suffix forming plural entities, from Mid.Pers. -gânag, -gâna.

A group of three stars visually or physically associated with each other. → triple system.

→ triple; → star

A system of three stars which are physically associated among them.

→ triple; → system

A group or set of three of one kind.
Optics: A compound lens made up of three elements that may or may not be cemented.

From trip-, from → triple + -et, from → doublet.

Setâyé, from setâ, → triple, + -(y)é nuance suffix.

The electronic state of an atom or molecule which has two unpaired electrons, and therefore whose total spin angular momentum is equal to 1.

→ triplet; → state.

An ancient astronomical instrument first described by Ptolemy in the Almagest, used in measuring the → altitude of a celestial body. It consisted of three long arms of wood. The first is perpendicular to the → horizon; the second is connected at the head of the first with an axis. The third had a graduated scale. An object was sighted along one arm and its → zenith distance was read on the graduated scale. It performed the same function as the → quadrant. Also called parallactic rulers, Ptolemy's rulers.

L. neuter of triquetrus "three corned," from tri-→ three + -quetrus "corned."

Se-šâx, literally "three corned," from se, → three, + šâx "→ branch, horn."

Unstable heavy → isotope of → hydrogen whose nucleus contains one → proton and two → neutrons. Tritium occurs naturally due to → cosmic rays interacting with atmospheric gases. In the most important reaction for natural tritium production, a fast neutron interacts with atmospheric nitrogen: ¹⁴N + n → ¹²C + ³T. Its → half-life is about 12 years. Tritium was formed in an intermediate step in light element synthesis in → early Universe.

N.L., from Gk. trit(os) "third" (from → tri- + -tos adj. suffix) + N.L. → -ium.