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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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.

habitable
  زیست‌پذیر   
zistpazir

Fr.: habitable   

In → exobiology, having a → temperature range within which → liquid water can exist on the surface of a → planet.

M.E., from O.Fr. habitation, from L. habitare "to live, dwell," frequentative of habere "to have, to hold, possess," from PIE base *ghrebh- "to seize, take, hold, have, give, receive" (cf. Mod.Pers. gereftan "to take, seize;" Mid.Pers. griftan; O.Pers./Av. grab- "to take, seize;" Skt. grah-, grabh- "to seize, take," graha "seizing, holding, perceiving;" M.L.G. grabben "to grab," from P.Gmc. *grab, E. grab "to take or grasp suddenly"); → zone.

Zistpazir, from zist, → life, + pazir "admitting, accepting, having," → -able.

habitable zone (HZ)
  زُنار ِ زیست‌پذیر   
zonâr-e zistpazir

Fr.: zone habitable   

A zone around a → star where the → temperature would be in the range 0-100 °C to sustain → liquid water on the surface of rocky planets (or sufficiently large moons). Water is thought to be a necessary component to the → formation and evolution of Earth-type life. This zone depends on the parent star's luminosity and distance; it will be farther from hotter stars. A more accurate definition of HZ needs to include other factors, such as orbital → eccentricity, heat sources other than stellar irradiation, and atmospheric properties. Same as → circumstellar habitable zone; → ecosphere.

habitable; → zone.

horseshoe orbit
  مدار ِ نعلی   
madâr-e na'li

Fr.: orbite en fer à cheval   

A periodic orbit which passes around the → Lagrangian points L4, L3, and L5, but neither of the two primaries. This orbit is shaped like a horseshoe when viewed in a reference frame rotating with the primaries. Such orbits occur in the solar system, for example in the case of the satellites → Janus and → Epimetheus, which share the same orbit around → Saturn. The smaller Epimetheus encompasses both the L4 and L5 points associated with the larger Janus and performs a horseshoe orbit relative to Saturn and Janus. The satellites experience a close approach every 4 years during which their orbits are exchanged. → tadpole orbit.

horseshoe mounting; → orbit.

hyperbolic orbit
  مدار ِ هذلولی   
madâr-e hozluli (#)

Fr.: orbite hyperbolique   

An orbit that is an open curve whose ends get wider apart at any rate between that of an ellipse and a straight line. Some comets' orbits become hyperbolic through the gravitational influence of a planet the comet passes near.

hyperbolic; → orbit.

innermost stable circular orbit (ISCO)
  درونیترین مدار ِ دایره‌ای ِ پایدار   
darunitarin madâr-e dâyere-yi-ye pâydâr

Fr.: orbite circulaire stable intérieur   

The smallest → circular orbit in which a particle can stably orbit a → black hole according to → general relativity without the risk of falling past the → event horizon. In other words, the ISCO is the inner edge of the → accretion disk around a black hole. Therefore, characteristics of accretion disks depend on ISCO. The radius of ISCO is calculated to be three times the → Schwarzschild radius (3 RSch). ISCO is closer to event horizon for rotating black hole.

inner; → stable; → circular; → orbit.

Keplerian orbit
  مدار ِ کپلری   
madâr-e Kepleri (#)

Fr.: orbit keplérienne   

The orbit of a spherical object of a finite mass around another spherical object, also of finite mass, governed by their mutual → gravitational forces only.

Keplerian; → orbit.

Lissajous orbit
  مدار ِ لیساژو   
madâr-e Lissajous

Fr.: orbite de Lissajous   

A quasi-periodic path resembling a → Lissajous figure around the L1 or L2 → Lagrangian points of a two-body system. Lissajous orbits, resulting from a combination of planar and vertical components, are used by certain space telescopes (such as → WMAP, → Planck Satellite, and → Herschel Satellite) that are required to be in a stable position relative to the Earth and Sun while making long-term observations.

Lissajous figure; → orbit.

lunar orbit node
  گره ِ مداری ِ ماه   
gereh-e madâri-ye mâh

Fr.: nœud de l'orbite lunaire   

Same as → lunar node.

lunar; → orbit; → node.

lunar sidereal orbital period
  دوره‌ی ِ مداری ِ اختری ِ مانگ   
dowre-ye madâri-ye axtari-ye mâng

Fr.: période orbitale sidérale de la Lune   

Same as → sidereal month.

lunar; → sidereal; → orbital; → period.

minimum orbit intersection distance (MOID)
  دورای کمینه‌ی ِ اندرسکنج ِ مدار   
durâ-ye kamine-ye andarsekanj-e madâr

Fr.: distance minimale d'intersection d'une orbite   

The minimum distance between the paths of two orbiting objects around a → primary. Such distance between an object and Earth is called Earth MOID.

minimum; → orbit; → intersection; → distance.

orbit
  مدار   
madâr (#)

Fr.: orbite   

The path followed by a body moving in a gravitational field. For bodies moving under the influence of a centrally directed force, without significant perturbation, the shape of the orbit must be one of the conic section family of curves (circle, ellipse, parabola, or hyperbola).

L. orbita "wheel track, course, circuit."

Madâr, from Ar.

orbit decay
  تباهیِ مدار   
tabâhi-ye madâr

Fr.: déclin d'orbite   

A gradual change in the orbit of a spacecraft caused by aerodynamic drag of a planet's outer atmosphere and other forces.

orbit; → decay.

orbital
  ۱) مداری؛ ۲) مدارال   
1) madâri; 2) madârâl

Fr.: 1) orbital; 2) orbitale   

1) Of or relating to an orbit.
2) A wave function that describes the state of an electron with a given energy (n, l, and ml quantum numbers) in an atom (atomic orbital) or in a molecule (molecular orbital).

Orbital, from → orbit + → -al.

orbital angular momentum
  جنباک ِ زاویه‌ای ِ مداری   
jonbâk-e zâviyeyi-ye madâri

Fr.: moment cinétique orbital, ~ angulaire ~   

1) Mechanics: The → angular momentum associated with the motion of a particle about an origin, equal to the cross product of the position vector (r) with the linear momentum (p = mv): L = r x p. Although r and p are constantly changing direction, L is a constant in the absence of any external force on the system. Also known as orbital momentum.
2) Quantum mechanics: The → angular momentum operator associated with the motion of a particle about an origin, equal to the cross product of the position vector with the linear momentum, as opposed to the → spin angular momentum. In quantum mechanics the orbital angular momentum is quantized. Its magnitude is confined to discrete values given by the expression: ħ &radic l(l + 1), where l is the orbital angular momentum quantum number, or azimuthal quantum number, and is limited to positive integral values (l = 0, 1, 2, ...). Moreover, the orientation of the direction of rotation is quantized, as determined by the → magnetic quantum number. Since the electron carries an electric charge, the circulation of electron constitutes a current loop which generates a magnetic moment associated to the orbital angular momentum.

orbital; → angular; → momentum.

orbital axis
  آسه‌ی ِ مداری   
âse-ye madâri

Fr.: axe orbital   

The → perpendicular to the → orbital plane.

orbital; → axis.

orbital debris
  تیفالِ مداری   
tifâl-e madâri

Fr.: débris spatial   

Objects in orbit around Earth created by humans, that no longer serve any useful purpose. They consist of everything from entire spent rocket stages and defunct satellites to explosion fragments, paint flakes, dust, and slag from solid rocket motors, and other small particles. Also called space junk and space waste.

orbital; → debris .

orbital electron
  الکترونِ مداری   
elektron-e madâri (#)

Fr.: électron orbital   

An electron contained within an atom which may be thought of as orbiting around the nucleus, in a manner analogous to the orbit of a planet around the Sun.

orbital; → electron .

orbital element
  بُن‌پارِ مداری   
bonpâr-e madâri

Fr.: élément orbital   

Any of the six parameters needed to specify the → orbit of an object around a → primary body (such as a planet around the Sun or a satellite around the Earth) and give its position at any instant. Two of them define the size and the form of the orbit: → semi-major axis (a) and → eccentricity (e). Three angular values determine the orbit position in space: the → inclination (i) of the object's → orbital plane to the reference plane (such as the → ecliptic), the → longitude of ascending node (Ω), and the → argument of periapsis (ω). And finally the sixth element is the → time of periapsis passage which allows calculating the body's position along the orbit at any instant.

orbital; → element.

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