An Etymological Dictionary of Astronomy and Astrophysics

فرهنگ ریشه شناختی اخترشناسی-اخترفیزیک

M. Heydari-Malayeri    -    Paris Observatory



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Number of Results: 62 Search : sphere
  شیدسپهر، رخشان‌سپهر   
šidsepehr, raxšânsepehr

Fr.: photosphère   

1) The visible surface of the Sun (temperature 5700 K), just below the → chromosphere and just above the → convective zone. The solar photosphere is a thin layer of roughly 300 km wide. Its temperature decreases uniformly with height, from about 6,600 K (pressure 0.868 → millibars) at its bottom, to about 4,400 K (pressure 125 mb), where it merges with the chromosphere. The photosphere has a "rice-grain" appearance, called → granulation, caused by rising (hot) and falling (cool) material in the → convective cells just below the photosphere. Other main features of the photosphere are → sunspots, → faculae, and → supergranulation.
2) The region of a star which gives rise to the continuum radiation emitted by the star.

photo- + → sphere.

plane-parallel atmosphere
  هواسپهر ِ پراسو-تخت، جو ِ ~   
havâsepehr-e parâsu-taxthâ, javv-e ~

Fr.: atmosphère plan-parallèle   

An approximation used in many stellar atmosphere models that depict the atmosphere as being only one-dimensional and bounded at the top and bottom by horizontal plane surfaces normal to the direction of gravity.

plane; → parallel; → atmosphere.

  تخت-سپهر، تخت-کره   
taxt-sepehr, taxt-koré

Fr.: planisphère   

A projection or representation of the whole or a part of a sphere on a plane. In particular, a polar projection of the celestial sphere or the Earth on a plane.

plani-; → sphere.


Fr.: plasmasphère   

In the magnetosphere, a region of relatively cool (low energy) and dense plasma that may be considered an outer extension of the ionosphere with which it is coupled. Like the ionosphere, the plasmasphere tends to co-rotate with the Earth.

plasma + → sphere.

Poincaré sphere
  کره‌ی ِ پو‌آنکاره   
kore-ye Poincaré

Fr.: sphère de Poincaré   

A representation that permits an easy visualisation of all different states of → polarization of a vector wave. The equator represents → linear polarization; the north pole corresponds to right-circular and the south pole to left- → circular polarization.

Named after Henri Poincaré (1854-1912), French mathematician and theoretical physicist, and a philosopher of science; → sphere.

pulsar magnetosphere
  مغنات‌سپهر ِ پولسار   
meqnâtsepehr-e pulsâr

Fr.: magnétosphère de pulsar   

A dense zone of magnetized → plasma surrounding a → pulsar. The magnetosphere, lying between the surface of the → neutron star and the → light cylinder, corotates with the pulsar like a rigid body under the effect of strong magnetic field. The magnetosphere's thickness is determined by the constraint that the corotation velocity of its upper surface should not exceed the → speed of light.

pilsar; → magnetosphere.

reducing atmosphere
  جوّ ِ باز‌هازنده، هواسپهر ِ ~   
javv-e bâzhâzandé, havâsepehr-e ~

Fr.: atmosphère réductrice   

1) An atmospheric condition in which oxidation is prevented by removal of oxygen and other oxidating gasses or vapours. Usually nitrogen or hydrogen gas is used in order to produce specific effects, e.g. on ceramic wares being fired.
2) An atmosphere of a planet or moon which has a high hydrogen content, either in the form of free hydrogen or hydrogen-containing compounds, such as methane or ammonia. The early atmosphere of Earth is thought to be reducing, dominated by carbon dioxide.

Reducing verbal adj. of → reduce; → atmosphere.

secondary atmosphere
  جوّ ِ دومان، هواسپهر ِ ~   
javv-e dovomân, havâsepehr-e ~

Fr.: atmosphère secondaire   

An atmosphere of a planet that forms after primordial gases had been lost or had failed to accumulate. A secondary atmosphere develops from internal volcanic outgassing, or by accumulation of material from comet impacts. It is characteristic of terrestrial planets, such as Earth, Mercury, Venus, and Mars. → primordial atmosphere.

secondary; → atmosphere.

singular isothermal sphere
  کره‌ی ِ ایزودمای ِ تکین   
kore-ye izodamâ-ye takin

Fr.: sphère isotherme singulère   

In models of star formation, an isothermal sphere in which the density distribution in the static or nearly static outer envelope obeys an r-2 power law. In the limit of infinite central concentration, the unstable equilibrium approaches the singular isothermal sphere which has the density and mass distributions ρ(r) = (a2/2πG)r-2 and M(r) = (2a2/G)r, where a is the isothermal → sound speed inside the cloud, G is the → gravitational constant, and r the distance from the center (F. H. Shu, 1977, ApJ 214, 488).

singular; → isothermal; → sphere.

southern hemisphere
  نیم‌سپهر دشتری   
nimsepehr-e daštari

Fr.: hémisphère sud   

The half of the → Earth or another → north pole between the → south pole and the → equator.

southern; → hemisphere.

Spectro-Polarimetric High-contrast Exoplanet (SPHERE)

Fr.: Spectro-Polarimetric High-contrast Exoplanet (SPHERE)   

The → extreme adaptive optics system and → coronagraphic facility at the → European Southern Observatory (ESO) → Very Large Telescope (VLT) (UT3) available from May 2014. Its primary science goal is imaging, low-resolution spectroscopic, and polarimetric characterization of → exoplanetary system at → visible and → near-infrared wavelengths (0.5-2.32 μm). SPHERE is capable of obtaining → diffraction-limited images at 0''.02 to 0''.08 resolution depending on the wavelength. Its → spectral resolution is 30 to 350, depending on the mode.

spectro-; → polarimetric; → high; → contrast; → exoplanet.

  کُره، سپهر   
koré (#), sepehr (#)

Fr.: sphère   

A solid geometric figure generated by the revolution of a semicircle about its diameter; equation: x2 + y2 + z2 = r2.

M.E. spere, from O.Fr. espere, from L. sphæra "globe, ball, celestial sphere," from Gk. sphaira "globe, ball," of unknown origin.

Koré, loan from Ar. kurat.
Sepehr "sphere, celestial globe, heavens, sky;" Mid.Pers. spihr "sphere, sky, firmament, fate;" Av. spiti- in compounds: spiti-dôiθra- "with clear eyes;" Proto-Iranian *spiθra- (in proper name); cf. Skt. śvitrá- "white, whitish."

sphere of influence
  سپهر ِ هنایش   
sepehr-e hanâyeš

Fr.: sphère d'influence   

The region of space around one of the bodies in a system of two celestial bodies where a third body of much smaller mass is influenced by the gravitational field of that body. The sphere of influence of a planet with respect to the Sun has a radius given by: R = RP(MP/MS)2/3, where RP is the radius of the planet's orbit around the Sun, MP is the mass of the planet, and MS is the solar mass. The sphere of influence of the Earth has a radius of about 927,000 km or slightly under 150 Earth radii. Beyond this limit, a space probe will come under the influence of the Sun.

sphere; → influence.

spheres of Eudoxus
  سپهرهای ِ اءودوکسوس   
sepehrhâ-ye Eudoxus

Fr.: sphères d'Eudoxe   

A series of spheres with varying radii centred on the Earth, each rotating uniformly about an axis fixed with respect to the surface of the next larger sphere, all comprising a model in Greek astronomy to describe the motions of the heavenly bodies. The spheres turned with different speeds about axes with different orientations. The fixed stars revolved around the Earth by the motion of the most distant sphere to which the stars were thought to be attached. Each of the five planets' (Mercury, Venus, Mars, Jupiter, and Saturn) motion could be described using four spheres. The Sun and the Moon required three spheres each to explain their motions. Therefore, a total of 27 spheres described the behavior of the heavenly bodies in terms of circular motion. Eudoxus was the first person to devise a model that could explain the → retrograde motion of the planets in the sky along a looped curve known as the → hippopede.

sphere; Eudoxus (Ευδοξοσ) of Cnidus (c 408 BC - c 355 BC), Greek astronomer and mathematician.

standard atmosphere
  هواسپهر ِ استانده، جوّ ِ ~   
havâsepehr-e estândé (#), javv-e ~ (#)

Fr.: atmosphère standard   

A hypothetical vertical distribution of atmospheric temperature, pressure, and density that, by international agreement, is taken to be representative of the atmosphere for purposes of pressure altimeter calibrations, aircraft performance calculations, aircraft and missile design, ballistic tables, etc.

standard; → atmosphere.

stellar atmosphere
  جوّ ِ ستاره‌ای، هواسپهر ِ ~   
javv-e setâre-yi, havâsephre ~

Fr.: atmosphère stellaire   

The outer envelope of gas and plasma that surrounds a star; characterized by pressure, temperature, density, chemical composition, and opacity at varying altitudes.

stellar; → atmosphere.

stellar atmosphere model
  مدل ِ جو ِ ستاره   
model-e javv-e setâré

Fr.: modèle d'atmosphère stellaire   

A model that computes the radiation field crossing the boundary layers of a star at all frequencies. The parameters used for the characterization of a stellar atmosphere model are: → effective temperature, → surface gravity, and → metallicity.

stellar; → atmosphere; → model.


Fr.: stratosphère   

The second major layer of Earth's atmosphere, just above the → troposphere and below the → mesosphere, extending from about 20 km to 90 km above the Earth. It is characterized by little vertical increase in temperature.

From Fr. stratosphère, literally "sphere of layers," coined by Fr. meteorologist Léon-Philippe Teisserenc de Bort (1855-1913) from L. stratus "a spreading out" (from p.p. stem of sternere "to spread out") + -sphère (→ sphere), as in atmosphère.

Cine-sepehr, from Ciné, → stratum, + sepehr, → sphere.

Stromgren sphere
  سپهر ِ استرومگرن، کره‌ی ِ ~   
sepehr-e Stömgren, kore-ye ~

Fr.: sphère de Strömgren   

A theoretical sphere of → ionized hydrogen created by energetic → ultravioletphotons of a hot, → massive star embedded in a uniform interstellar → molecular cloud and lying at the center of the sphere. → H II region.

Named after Bengt Strömgren (1908-1987), a Danish astrophysicist, who put forward the first and simplest version of the model in 1939; → sphere.


Fr.: thermosphère   

The region of the upper atmosphere in which temperature increases continuously with height, starting at roughly 100 km. The thermosphere includes the exosphere and most of the ionosphere.

thermo-; → sphere.

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