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

A coordinate positioning tool, using a combination of satellites that can rapidly and accurately determine the → latitude, → longitude, and the → altitude of a point on or above the Earth's surface. The GPS is based on a constellation of 24 Earth-orbiting satellites at an altitude of about 26,000 km. The system is a direct application of the thories of → special relativity and → general relativity.

→ global; → positioning; → system.

The hypothetical particle, in the → quantum chromodynamics theory, that carries the force between → quarks. There are eight independent types of gluon.

From glue (O.Fr. glu, from L.L. glus "glue," from L. gluten "glue") + → -on.

1) A rod oriented in such a way that its shadow, cast by the Sun's rays, shows the hours on a → sundial; a style.
2) A device used in ancient times consisting of a vertical shaft used to measure the altitude of the Sun and hence to determine the time of day.

From L. gnomon, from Gk. gnomon "carpenter's square, rule; indicator," literally "one who discerns," from gignoskein "to know, think, judge," cognate with L. gnoscere, noscere "to come to know" (Fr. connaître; Sp. conocer); O.Pers./Av. xšnā- "to know, learn, come to know, recognize;" Mid.Pers. šnâxtan, šnâs- "to know, recognize," dânistan "to know;" Mod.Pers. šenâxtan, šenâs- "to recognize, to know," dânestan "to know;" Skt. jñā- "to recognize, know," jānāti "he knows;" P.Gmc. *knoeanan; O.E. cnawan, E. know; Rus. znat "to know;" PIE base *gno- "to know."

Bâhu "stick, staff; arm (from the elbow to the shoulder)," related to bâzu "arm," Mid.Pers. bâzûk "arm;" Av. bāzu- "arm;" cf. Skt. bāhu- "arm, forearm," also "the shadow of the gnomon on a sundial; the bar of a chariot pole;" Gk. pechys "forearm, arm, ell;" O.H.G. buog "shoulder;" Ger. Bug "shoulder;" Du. boeg; O.E. bôg, bôh "shoulder, bough;" E. bough " a branch of a tree;" PIE *bhaghu- "arm."

The projection of a spherical surface onto a plane through a point. A gnomonic → map projection displays all great circles as straight lines, and therefore indicates the shortest path between two points. Small circles are projected as conic sections.

→ gnomon; → -ic; → projection.

Every number greater than 2 is the sum of two → prime numbers. Goldbach's number remains one of the most famous unsolved mathematical problems of today.

Named after the German mathematician Christian Goldbach (1690-1764); → conjecture.

A → geochemical classification scheme in which → chemical elements on the → periodic table are divided into groups based on their → affinity to form various types of compounds: → lithophile, → chalcophile, → siderophile, and → atmophile. The classification takes into account the positions of the elements in the periodic table, the types of electronic structures of atoms and ions, the specifics of the appearance of an affinity for a particular → anion, and the position of a particular element on the → atomic volume curve.

Developed by Victor Goldschmidt (1888-1947); → classification.

1) Marking the scale of an instrument, e.g. the stem of a thermometer is graduated in degrees.
2) An act of graduating; the state of being graduated.

Verbal noun of → graduate.

Sticking together of micron- to centimetre-sized grains occurring in the interstellar and protoplanetary environments to form larger grain agglomerates.

→ grain; → coagulation.

Conversion of dust grains into smaller grains due to high environmental temperatures.

→ grain; → evaporation.

The process by which dust grains are assembled or produced.

→ grain; → formation.

The mottled appearance of the solar → photosphere, caused by → convective cells, resembling → granules, which rises from the interior of the Sun. Each granule has a mean size of about 1,000 km and an upward velocity of about 0.5 km/sec. Granules are separated by intergranular walls about 400 K colder. They emerge from the fragments of the preceding granules and their lifetimes are about 20 minutes.

From → granule + -ation a combination of -ate and -ion, used to form nouns from stems in -ate.

Dâne-bandi, from dâné, → grain, + bandi verbal noun of bastan, vastan "to bind, shut;" O.Pers./Av. band- "to bind, fetter," banda- "band, tie" (cf. Skt. bandh- "to bind, tie, fasten;" PIE *bhendh- "to bind;" Ger. binden; E. bind).

1) The universal phenomenon of attraction between material bodies. → Newton's law of gravitation.
2) The act or process of moving under the influence of this attraction.

Verbal noun of → gravitate.

Of or relating to or caused by → gravitation.

Adj. of → gravitation.

The acceleration caused by the force of gravity. At the Earth's surface it is determined by the distance of the object form the center of the Earth: g = GM/R², where G is the → gravitational constant, and M and R are the Earth's mass and radius respectively. It is approximately equal to 9.8 m s^-2. The value varies slightly with latitude and elevation. Also known as the → acceleration of gravity.

→ gravitational; → acceleration.

The force that pulls material bodies toward one another because of → gravitation.

→ gravitational; → attraction.

Collapse of a mass of material as a result of the mutual → gravitational attraction of all its constituents.

→ gravitational; → collapse.

A fundamental constant that appears in → Newton's law of gravitation. It is the force of attraction between two bodies of unit mass separated by unit distance: G = 6.673 x 10^-8 dyn cm² g^-2 or 6.673 x 10^-8 cm³s^-2g^-1, or 6.673 x 10^-11 N m² kg^-2 or 6.673 x 10^-11 m³s^-2kg^-1. It was first measured in 1798 by Henry Cavendish (1731-1810), 71 years after Newton's death. Same as the → Newtonian constant of gravitation.

→ gravitational; → constant.

Decrease in the volume of an astronomical object under the action of a dominant, central gravitational force.

→ gravitational; → contraction.

The dimensionless gravitational constant defined as the gravitational attraction between pair of electrons and normally given by: α_G = (Gm_e²) / (ħc) = (m_e / m_P)² ~ 1.7518 × 10^-45, where ħ is → Planck's reduced constant, c the → speed of light, m_e is the → electron mass, and m_P is the → Planck mass.

→ gravitational; → coupling; → constant.

An encounter in which two moving bodies alter each other's direction and velocity by mutual → gravitational attraction.

→ gravitational; → encounter.