An Etymological Dictionary of Astronomy and Astrophysics
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فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory

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Number of Results: 3106 Search : on
general precession
  پیشایان ِ هروین   
pišâyân-e harvin

Fr.: précession générale   

The secular motions of the → celestial equator and → ecliptic. In other words, the sum of → lunisolar precession, → planetary precession, and → geodesic precession.

general; → precession

general precession in longitude
  پیشایان ِ هروینِ درژنا   
pišâyân-e harvin-e derežnâ

Fr.: précession générale en longitude   

The secular displacement of the → equinox on the → ecliptic of date.

general; → precession; → longitude.

general precession in right ascension
  پیشایان ِ هروین ِ راست‌افراز   
pišâyân-e harvin-e râst afrâz

Fr.: précession générale en ascension droite   

The secular motion of the → equinox along the → celestial equator.

general; → precession; → right ascension.

generalization
  هروین‌کرد، هروینش   
harvinkard, harvineš

Fr.: généralisation   

The act or process of generalizing; → generalize.
A result of this process; a general statement, proposition, or principle.

Verbal noun of → generalize.

generation
  آزانش   
âzâneš

Fr.: génération   

1) A coming into being.
2) The → production of → energy (→ heat or → electricity).

Verbal noun of → generate.

geocentric longitude
  درژنای ِ زمین-مرکزی   
derežnâ-ye zamin-markazi

Fr.: longitude géocentrique   

The same as → geodetic longitude.

geocentric; → longitude.

geocorona
  زمین‌تاج   
zamin-tâj (#)

Fr.: géocouronne   

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.

geodesic precession
  پیشایان ِ کهین‌رهی   
pišâyân-e kehinrahi

Fr.: précession géodésique   

geodesic precession.

geodesic; → precession

geodetic longitude
  درژنای ِ زمین‌سنجیک   
derežnâ-ye zamin-sanjik

Fr.: longitude géodésique   

The angle between the plane of the → geodetic meridian and the plane of of the geodetic meridian through the site of the → Airy transit circle at the Royal Greenwich Observatory.

geodetic; → longitude.

geodetic precession
  پیشایان ِ کهین‌رهی   
pišâyân-e kehinrahi

Fr.: précession géodésique   

A → relativistic effect on the precession motion of a gravitational system due to the → curvature of the → space-time. When a body revolves around a primary, the → rotation axis of the orbiting body follows the curvature of spece-time. Over time the space-time warping causes the spin axis to precess. In the case of the Earth-Moon system, this means a small → direct motion of the → equinox along the → ecliptic, amounting to 1''.915 per century. The geodetic precession is given by: ψg = (3/2) k2 (1 - e) n, where k is the → constant of aberration (in radians), e the → eccentricity of the Earth and n the mean angular orbital motion of the Earth (in arcsec/cy). Also called → Einstein-de Sitter effect and → geodesic precession.

geodetic; → precession

geodetic refraction
  شکست ِ زمین‌سنجیک   
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
  زچار ِ زمین‌مغناتی   
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
  افق ِ هندسی   
ofoq-e hendesi

Fr.: horizon géométrique   

Where the apparent → sea horizon would be if there were no → atmospheric refraction.

geometric; → horizon.

geometric progression
  فرایازی ِ هندسی   
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. The sum of the first n terms is given by: Sn = a(1 - rn)/(1 - r). Also called → geometric sequence.

geometric; → progression.

geometrical libration
  رخگرد ِ هندسی   
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.

geometric; → libration.

geostationary orbit
  مدار ِ زمین‌ایست‌وّر   
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
  مدار ِ زمین‌همگام   
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
  ناحیه‌ی ِ II H یِ غولپیکر   
nahiye-ye H II-ye qulpeykar

Fr.: région H II géante   

An → H II region emitting at least 1050 → 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.

giant; → H II; → region.

Gibbs canonical distribution
  واباژش ِ هنجاروار ِ گیبس   
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
  کریای ِ گیبس   
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.

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