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

Of or relating to → astronomy.
In non astronomical contexts, of enormous magnitude; immense.

Astronomical, from L. astronomic(us), → astronomy + → -ic, + → -al adj. suffix.

Axtaršenâxti, from axtaršenâxt, variant of axtaršenâsi, → astronomy + -i adj. suffix.
Axtaršenâsik, from axtaršenâsi, → astronomy + re-introduced Mod.Pers. suffix -ik, → -ics.

A precise pendulum clock with separate dials for seconds, minutes, and hours. It was originally used by astronomers to calculate astronomical time.

→ astronomical; → clock.

A precisely measured fundamental quantity in astronomy, such as the → solar parallax, the → constant of aberration, and the → obliquity of the ecliptic.

→ astronomical; → constant.

Values in a reference system used to relate the position of a body on the celestial sphere.

→ astronomical; → coordinates.

The intersection of a plane perpendicular to the radius of the Earth through the observer's eye with the celestial sphere. Same as → true horizon. Because the → celestial sphere has an infinite radius, two observers at different heights above sea level, but placed on the same vertical line, have the same astronomical horizon. Because of → dip of the horizon, the astronomical horizon always lies above the → sea horizon. But on land it is usually hidden by trees, hills, and buildings which determine the observer's → apparent horizon.

→ astronomical; → horizon.

A device used to observe and study → astronomical objects.

→ astronomical; → instrument.

The angle between the → equatorial plane and the true → vertical at a point on the surface.

→ astronomical; → latitude.

A naturally occurring physical entity or association that lies beyond the Earth's atmosphere and can be studied observationally. In other words, a gravitationally bound structure that is associated with a position in space, but may consist of multiple independent astronomical objects. A list of astronomical objects includes → planets, → asteroids, → comets, → stars, → nebulae, galaxies (→ galaxy), → galaxy clusters, → pulsars, and → black holes. Note that → celestial body, → celestial object, and → heavenly body are less technical terms for these entities.

→ astronomical; → object.

A building, place, or institution designed and equipped for making → observations of astronomical phenomena.

→ astronomical; → observatory.

The → angular → displacement of a point on the → celestial sphere due to the Earth's → atmospheric refraction.

→ astronomical; → refraction.

A certain place whose characteristics, as to location, altitude, atmospheric conditions, etc., make it appropriate for astronomical observations.

→ astronomical; → site.

One of a set of tables giving parameters used for calculations of positions of the Sun, the Moon, and the planets in particular in pre-telescopic astronomy. The oldest known astronomical tables are those of Ptolemy. In Modern astronomy it is usually replaced by the term → ephemeris. Same as → zij. See also → Toledan Tables, → Alfonsine Tables.

→ astronomical; → table.

One of the twilight phases when the Sun's center lies between 12 and 18 degrees below the horizon. Astronomical twilight is followed or preceded by → nautical twilight. Most stars and other celestial objects can be seen during this phase. However, some of the fainter stars and galaxies may not be observable as long as the Sun is less than 18 degrees below the horizon. See also → civil twilight.

→ astronomical; → twilight.

1) A unit of length equal to 149 597 870 700 m exactly, with symbol "au" (re-definition at the International Astronomical Union's 28th General Assembly in Beijing, China, August 20-31). The astronomical unit equals 1.5813 × 10^-5 → light-years and 4.8481 ×10^-6 → parsecs.
2) Previous definition: The radius of a circular orbit in which a body of negligible mass, and free of perturbations, would revolve around the Sun in 2 π / k days, where k is the → Gaussian gravitational constant. This is slightly less than the semi-major axis of the Earth's orbit.

→ astronomical; → unit.

A time scale previously used in calculations of the orbits of solar system objects (planets, asteroids, comets, and interplanetary spacecrafts). It was based on the Terrestrial Dynamical Time, but took the relativistic effect of time dilation into account to move the origin to the solar system barycenter. It is now superseded by → Barycentric Coordinate Time (TCB).

→ barycenter; → dynamical; → time.

Of, relating to, used in, or produced by means of chemistry.

From chemic "of alchemy," → chemistry + → -al.

Šimiyâyi, of or pertaining to šimi→ chemistry.
Šimik, from šim- + -ik, → -ic.

The relative amount of a given → chemical element or → chemical compound with respect to another element or compound in a given sample.

→ chemical; → abundance.

Same as → chemisorption.

→ chemical; → adsorption.

The extent to which a chemical species, such as an atom or molecule, tends to combine with another to form a chemical compound.

→ chemical; → affinity.

A force by which chemical substances are held together by attraction of atoms to each other through sharing, as well as exchanging, of electrons.

→ chemical; → bond.