aberration orbit madâr-e birâheš Fr.: orbite d'aberration The apparent path described by a star on the → celestial sphere due → annual aberration. A star at the → ecliptic pole is seen to move around a circle of angular radius about 20".50, once a year. A star on the → ecliptic oscillates to and fro along a line of angular half-length 20".50. At an intermediate → celestial latitude, β, the aberration orbit is an ellipse, with semi-major axis 20".50 and semi-minor axis (20".50) sin β. → aberration; → orbit. |
bound orbit madâr-e bandidé Fr.: orbite liée The orbit described by an object around a central gravitational force in a system whose total energy is negative. An elliptical orbit. |
circular orbit madâr-e dâyere-yi, ~ parhuni Fr.: orbite circulaire The path of a object in → circular motion. |
co-orbital ham-madâr Fr.: co-orbital Of or relating to two or more celestial bodies that share, or almost share, the same orbit. |
co-orbital motion jonbeš-e ham-madâri Fr.: mouvement co-orbital The motion of two or more bodies around the Sun on different orbits when it takes them the same amount of time to complete one revolution. There are three possible types of co-orbital motions of a small body associated with a planet: → tadpole orbits, → horseshoe orbits, and → quasi-satellite orbits. → co-orbital; → motion. |
co-orbital satellite mâhvâre-ye ham-madâr, bandevâr-e ~ Fr.: satellite co-orbital Any of satellites which either share the same orbit or which occupy immediately adjacent orbits that change periodically as the satellites approach one another (Ellis et al., 2007, Planetary Ring Systems, Springer). → co-orbital; → satellite. |
co-orbiting ham-madâri; ham-madâr Fr.: co-orbitage; c-orbitant, co-orbiteur The action or quality of a → co-orbiting asteroid. From co- "together," → com- + → orbit + → -ing. From ham- "together," → com- + madâr→ orbit + -i noun suffix. |
co-orbiting asteroid sayyârak-e ham-madâr Fr.: astéroïde co-orbiteur An asteroid having a → co-orbital motion. → co-orbiting; → asteroid. |
cometary orbit madâr-e donbâledâr Fr.: orbite de comète The → path followed by a → comet in the → solar system around the → Sun. Most cometary orbits appear to be → elliptical, or in some cases → parabolic. The orbits of → short-period comets are elliptical, carrying them out to a region lying from → Jupiter to beyond the orbit of → Neptune. Those of → long-period comets are very elliptical. The orbits may be strongly influenced if they pass near the Jovian planets, particularly Jupiter itself. The cometary orbits are also influenced to some degree by gases shooting out of comets, so their orbits are primarily but not completely determined by gravity. Newton (1644-1727) was the first to compute a cometary orbit. He found that the comet of 1680 was following a parabolic orbit around the Sun. Edmond Halley (1656-1742), following the methods of Newton, computed the → orbital elements of 24 comets. He realized that the comets of 1531, 1607 and 1682 had very similar elements and postulated that they were in fact the same object, orbiting an elongated ellipse. He predicted the next return to occur in 1758 or early 1759. The return of what is now called Halley's comet was observed after his death, This first observation of a "predicted" comet is manifestly one of the major successes of → celestial mechanics. |
commensurate orbits madârhâ-ye hammasâ Fr.: orbites commensurables Of two bodies orbiting around a common barycenter, when the orbital period of one is an exact fraction, for example one-half or two-thirds, of the other. → commensurate; → orbit. |
de-orbit vâmadâridan Fr.: désorbiter To cause a spacecraft to leave its operational orbit to enter a descent phase or to change course. |
de-orbiting vâmadâreš Fr.: désorbitage Of a spacecraft, the act or process of departing from an operational orbit. → de-orbit. Noun form of → de-orbit. |
elements of the orbit bonpârhâ-ye madâr, onsorhâ-ye ~ (#) Fr.: éléments orbitaux |
elongated orbit madâr-e derâzidé, ~ kašidé Fr.: orbite allongée An → elliptical orbit with a high → eccentricity. |
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. |
Hohmann transfer orbit madâr-e tarâvaž-e Hohmann Fr.: orbite de trandfer An elliptical orbit that is the most economical path for a spacecraft to take from one planet to another. In the case of Earth-Mars travel, the desired orbit's → perihelion will be at the distance of Earth's orbit, and the → aphelion will be at the distance of Mars' orbit. The portion of the solar orbit that takes the spacecraft from Earth to Mars is called its trajectory. Earth and Mars align properly for a Hohmann transfer once every 26 months. → Hohmann transfer. Named after Walter Hohmann (1880-1945), German engineer, who developed basic principles and created advanced tools necessary for the conquest of space. In 1925 he published The Attainability of the Heavenly Bodies in which he described the mathematical principles that govern space vehicle motion, in particular spacecraft transfer between two orbits. |
horseshoe orbit 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 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) 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 R_{Sch}). ISCO is closer to event horizon for rotating black hole. |