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

1) Relating to, measured from, or with respect to the center of the Earth.
2) Having the earth as a center. → geocentric coordinate system, → Geocentric Coordinate Time, → geocentric cosmology, → geocentric parallax, → geocentric system.

→ geo- + → center + -ic an adjective-forming suffix.

A coordinate system which has as its origin the center of the Earth.

→ geocentric; → coordinate; → system.

The proper time experienced by a clock at rest in a coordinate frame co-moving with the center of the Earth, i.e. a clock that performs exactly the same movements as the Earth but is outside the Earth's gravity well. TCG was defined in 1991 by the International Astronomical Union as one of the replacements for Barycentric Dynamical Time (TDB).

→ geocentric; → coordinate; → time.

A model of the Universe in which the Earth is centrally located and the Sun, planets, and stars revolve around the Earth.

→ geocentric; → cosmology.

The angle between the geocentric location vector and the → geodetic equator.

→ geocentric; → latitude.

The same as → geodetic longitude.

→ geocentric; → longitude.

The difference between the direction of an object as seen from a point on the surface of the Earth and the direction in which it would be seen from the Earth's center. Also known as → diurnal parallax.

→ geocentric; → parallax.

An ancient model of the Universe whereby all the celestial bodies travel around the Earth in circular orbits. Eudoxus of Cnidus (c. 390- c. 337 BC), one of Plato's pupils, maintained that all objects in the sky are attached to moving crystalline spheres, with the Earth at the centre. This model is often named → Ptolemaic system after its most famous supporter, the Greco-Roman astronomer Ptolemy.

→ geocentric; → system.

Of or relating to → geochemistry.

→ geochemistry; → -al.

A field of science that is concerned with the relative abundance, distribution, and the movement of → chemical elements in the → Earth's crust or other → solar system objects.

→ geo-; → chemistry.

The outermost part of Earth's atmosphere, a tenuous halo of hydrogen and some helium extending out to perhaps 15 Earth radii. It emits at the → Lyman alpha line (wavelength 121 nm) caused by → resonant scattering of solar → ultraviolet.

→ geo- + → corona.

1) The shortest distance between two points in space (or → space-time). A geodesic on a sphere is an → arc of a → great circle. In the theory of → general relativity, freely falling bodies follow geodesic paths in space-time.
2) → geodetic.

From Fr. géodésique, → geodesy; → -ic.

Kehinrah "shortest path," from kehin, superlative of keh "small, little, slender" (related to kâstan, kâhidan "to decrease, lessen, diminish," from Mid.Pers. kâhitan, kâstan, kâhênitan "to decrease, diminish, lessen;" Av. kasu- "small, little;" Proto-Iranian *kas- "to be small, diminish, lessen") + râh "path, way, road" (from Mid.Pers. râh, râs "way, street," also rah, ras "chariot;" from Proto-Iranian *rāθa-; cf. Av. raθa- "chariot;" Skt. rátha- "car, chariot," rathyā- "road;" L. rota "wheel," rotare "to revolve, roll;" Lith. ratas "wheel;" O.H.G. rad; Ger. Rad; Du. rad; O.Ir. roth; PIE base *roto- "to run, to turn, to roll").

The shortest line between two points on a surface. Also called → geodesic.

→ geodesic; → line.

→ geodesic precession.

→ geodesic; → precession

The study and measurement of the shape, size, and curvature of the Earth.

From Fr. géodésie, from Gk. geodaisia, from → geo- + dai(ein) "to divide" + -sia, variant of -ia a noun suffix.

Zamin-sanji, from zamin, → geo-, + sanji, from sanjidan "to measure; to compare," from Mid.Pers. sanjidan "to weigh," from present tense stem sanj-, Av. θanj- "to draw, pull;" Proto-Iranian *θanj-. Other terms from this base in Pers.: lanjidan "to pull up," hanjidan, âhanjidan "to draw out," farhang "education, culture."

A type of Earth observing satellite used to measure the location of points on Earth's surface with great accuracy. Their observations help determine the exact size and shape of Earth, act as references for mapping, and track movements of Earth's crust.

→ geodesy; → satellite

Of, relating to, or determined by → geodesy.

→ geodesy; → -ic.

A → coordinate system, composed of → geodetic latitude and → geodetic longitude on the → Earth's surface which is dependent on the figure and size of a particular model for the Earth's surface.

→ geodetic; → coordinate.

Any of the adopted values of → geodetic latitude, → geodetic longitude, or → azimuth at a selected location (an initial station) whose astronomical coordinates have already been determined.

→ geodetic; → datum.

The plane swept out as the generating ellipse of the → reference ellipsoid rotates about its minor axis.

→ geodetic; → equator.