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geodetic refraction šekast-e zamin-sanjik Fr.: réfraction géodésique The limiting case of → astronomical refraction when the light path is entirely within the Earth's atmosphere. → geodetic; → refraction. |
geomagnetic excursion zocâr-e zamin-meqnâti Fr.: excursion géomagnétique A geophysical event, distinguished from the → magnetic reversal, in which the Earth's magnetic field departs for a relatively short time from its usual near axial configuration, without establishing a reversed direction. During the excursion the intensity and direction of the Earth's magnetic field undergo drastic changes. Palaeomagnetic measurements have revealed that since the last full reversal the Earth's magnetic field has, for brief intervals, deviated from the behavior expected during "normal" secular variation. → geomagnetic; → excursion. |
geometric horizon ofoq-e hendesi Fr.: horizon géométrique Where the apparent → sea horizon would be if there were no → atmospheric refraction. |
geometric progression farâyâsi-e hendesi (#) Fr.: progression géométrique A → sequence in which the ratio of a term to its predecessor is the same for all terms. In general, the nth term has the form ar^{(n-1)}, where n is a positive integer, and a and r are nonzero constants; r is called the ratio or common ratio. Also called → geometric sequence. → geometric; → progression. |
geometrical libration roxgard-e hendesi (#) Fr.: libration géométrique Libration resulting from changes in the location of the observer with respect to body. More specifically, a lunar libration motion that results from the Earth based observer seeing the Moon from different directions at different times. There are three types of geometrical libration: → libration in longitude, → libration in latitude, and → diurnal libration. See also → physical libration. |
geostationary orbit madâr-e zamin-istvar Fr.: orbite géostationnaire A satellite orbit in the plane of the Earth's equator and 35,880 km above it, at which distance the satellite's period of rotation matches the Earth's and the satellite always remains fixed in the same spot over the Earth. Geostationary, from → geo- + → stationary; → orbit. |
geosynchronous orbit madâr-e zamin-hamgâm Fr.: orbite géosynchrone A circular orbit around the Earth identical to a geostationary orbit except that the satellite's orbit does not necessarily lie in the Earth's equatorial plane. → geo-; → synchronous; → orbit. |
giant H II region nahiye-ye H II-ye qulpeykar Fr.: région H II géante An → H II region emitting at least 10^{50} → Lyman continuum photons per second, or about 10 times → Orion nebula. Such an H II region should be powered by at least one O3V star or by at least a dozen → O-type and tens → B-type stars. Our nearest giant H II region is → NGC 3603. Some other Galactic giant H II regions are: → Lagoon Nebula, M17, W31, W51A, and NGC 3576. |
Gibbs canonical distribution vâbâžeš-e hanjârvâr-e Gibbs Fr.: distribution canonique de Gibbs The probability distribution of the various possible states of a certain → quasi-closed subsystem. → Gibbs free energy; → canonical; → distribution. |
Gibbs function karyâ-ye Gibbs Fr.: fonction de Gibbs Same as → Gibbs free energy. Named after Josiah Willard Gibbs (1839-1903), an American physicist who played an important part in the foundation of analytical thermodynamics; → function. |
Global Positioning System (GPS) râžmân-e nehešdâd-e jahâni Fr.: système de positionnement par satellites 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. |
gluon gluon (#) Fr.: gluon 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. |
gnomon bâhu Fr.: gnomon 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. 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." |
gnomonic projection farâšâneš-e bâhu-yi Fr.: projection gnomonique 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. |
Goldbach's conjecture hâšan-e Goldbach Fr.: conjecture de Goldbach 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. |
Goldschmidt classification radebandi-ye Goldschmidt Fr.: classification de Goldschmidt 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. |
graduation padâkeš, padâk dehi, padâk giri Fr.: graduation 1) Marking the scale of an instrument, e.g. the stem of a thermometer is graduated in
degrees. Verbal noun of → graduate. |
grain coagulation mâseš-e dâné Fr.: coagulation des grains Sticking together of micron- to centimetre-sized grains occurring in the interstellar and protoplanetary environments to form larger grain agglomerates. → grain; → coagulation. |
grain evaporation boxâreš-e dâné Fr.: évaporation des grains Conversion of dust grains into smaller grains due to high environmental temperatures. → grain; → evaporation. |
grain formation diseš-e dâné Fr.: formation des grains The process by which dust grains are assembled or produced. |
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