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

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."

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.

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.