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

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.

The direction of the Earth's instantaneous rotation pole. It differs from the pole due to the short time-scale (days or decades) variations called → nutation.

→ true; → celestial; → pole.

Same as → true celestial equator.

→ true; → equtor.

The intersection of the → ecliptic with the → true celestial equator for a given epoch. It is derived from the → mean equinox accounting for the → nutation.

→ true; → equinox.

A large circle of the → celestial sphere whose plane is perpendicular to the radius of the Earth through the point. Same as → astronomical horizon. The → visible horizon usually lies lower than the true horizon. See also → dip of the horizon.

→ true; → horizon.

The geographic north defined by the rotational pole of the Earth, as opposed to magnetic north defined by the geomagnetic north pole.

→ true; → north.

The coordinates of an object for a given date, with respect to the true equator and the true equinoxes for the instant of time in question.

→ true; → position.

The → sidereal time with respect to the → true equinox.

→ true; → sidereal; → time.

The Sun as seen in the sky, also referred to as the → apparent Sun; in opposition to → mean Sun.

→ true; → Sun.

A young → massive star cluster in the → Carina Nebula, lying about 10 arcmin to the north-west of → Trumpler 16. It comprises several → O-type stars. In particular, its core contains at least three very early O-type stars; → HD 93129.

From a catalog by Robert J. Trumpler (1886-1956), the Swiss-American astronomer who studied the → open clusters at Lick Observatory (1930). He was the first to produce a definite evidence of the existence of → interstellar reddening, due to → absorption, and to estimate its magnitude.

A → massive star, and the most populous cluster of the → Carina Nebula. It contains several → O-type stars and three known → Wolf-Rayet stars in addition to the famous → LBV star → Eta Carinae. Trumpler 16 is probably older than → Trumpler 14.

→ Trumpler 14.

To shorten by cutting off a part.
Math.: 1) To shorten a number by dropping a digit or digits; e.g. to shorten 3.438 to 3.4.
2) To remove portions of solids falling outside a set of symmetrically placed planes.

From L. truncatus "cut off," p.p. of truncare "to maim, cut off," from truncus "mutilated, cut off."

Kol kardan "to cut off the end of; to dock a tail," from kol "docked, short," variants in a large number of dialects: kola, kalta, kel, kelma, koc, kall, kor, kul in Gilaki, Tâleši, Lori, Malâyeri, Hamedâni, Qâeni, and others, cf. Av. kaurvô- "bald, docked," kaurvôduma- "with a bald tail," kaurvôgaoša- "with bald ears;" cf. Gk. kol(os) "docked" (kolouros "dock-tailed;" L. colurus) + kardan "to do, to make" (Mid.Pers. kardan, O.Pers./Av. kar- "to do, make, build," Av. kərənaoiti "makes," cf. Skt. kr- "to do, to make," krnoti "makes," karma "act, deed;" PIE base k^wer- "to do, to make").

The act or process of truncating, as → disk truncation.

Verbal noun from → truncate.

1) The quality of being true, genuine, actual, or factual.
2) Something that is → true as opposed to → false.
3) Logic: The correct corresponding of a → proposition with a → fact. See also → truth value, → partial truth.

M.E. treuthe; O.E. trêowth "faith, faithfulness, fidelity; quality of being true," from triewe, treowe "faithful," → tue, with suffix *-itho-th.

Noun from râstin, → true, + noun suffix -i.

A → total function from → truth values to truth values (a sequence of truth values).

→ truth; → function.

A table with columns and rows that lists the resultant → truth value of the given → sentences for each of the possible combinations of truth values to the simple sentences out of which the given sentences are constructed.

→ truth; → value.

The quality of a logical → proposition (or a formal → symbol) which describes the relation of a proposition to → truth. The traditional → formal logic admits only two contradictory values, → true or → false. In → symbolic logic, more specifically in → polyvalent logics, other truth values are used (such as possible, impossible, undetermined, probable, random, etc.).

→ truth; → value.

A huge wave, caused by undersea earthquakes, volcanic eruptions, or, more rarely, by asteroid or meteoroid impact (as in the case of the K-T extinction).

From Japanese tsunami, from tsu "harbor" + nami "waves."

1) A long hollow cylinder of metal, glass, rubber, or other material used to transport or contain liquids or gases.
2) An electronic device in which electrons operate in a gas or in vacuo inside a closed envelope.

M.E., from M.Fr. tube, from L. tubus "tube, pipe," of unknown origin.

Lulé "tube, pipe; roll," dialectal Lori, Laki lil, Laki lul "wanderer;" Hamadâni lul "spiral, coil."

Same as → flow tube.

→ tube; → tube.