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. |
habitable 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) 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. |
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. |
Keplerian orbit 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 orbital velocity tondâ-ye madâr-e Kepleri Fr.: vitesse d'orbite képlérienne The velocity of an object orbiting another object according to → Kepler's laws. |
Lissajous orbit 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 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. → minimum; → orbit; → intersection; → distance. |
orbit 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 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. |
orbital 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. |
orbital axis âse-ye madâri Fr.: axe orbital The → perpendicular to the → orbital plane. |
orbital debris 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. |