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.
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.
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.
habitable zone (HZ)
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.
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.
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.
innermost stable circular orbit (ISCO)
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.
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.
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.
lunar orbit node
gereh-e madâri-ye mâh
Fr.: nœud de l'orbite lunaire
Same as → lunar node.
lunar sidereal orbital period
dowre-ye madâri-ye axtari-ye mâng
Fr.: période orbitale sidérale de la Lune
Same as → sidereal month.
minimum orbit intersection distance (MOID)
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.
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.
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.
1) madâri; 2) madârâl
Fr.: 1) orbital; 2) orbitale
1) Of or relating to an orbit.
orbital angular momentum
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.
Fr.: axe orbital
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.
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.
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.