Fr.: coordonnées géodésiques
A → coordinate system, composed of → geodetic latitude and → geodetic longitude on the → Earth's surface which is dependent on the figure and size of a particular model for the Earth's surface.
→ geodetic; → coordinate.
geographic coordinate system
râžmân-e hamârâhâ-ye zaminnegârik
Fr.: système de coordonnées géographiques
A → ccordinate system on the surface of the Earth that defines every location by a set of numbers and letters, indicating the → latitude and → longitude.
→ geographic; → coordinate; → system.
horizon coordinate system
râžmân-e hamârâhâ-ye ofoqi
Fr.: coordonnées horizontales
The coordinate system based on the position of the observer. The horizontal plane is the fundamental plane and the coordinates are → altitude and → azimuth.
→ horizon; → coordinate; → system.
hamârâ-ye nâdidé engâshté
Fr.: coordonnée ignorée
A → generalized coordinate that does not appear explicitly in the → Lagrangian function. Also called → cyclic coordinate. Ignorable coordinates do not participate in the → Legendre transformation, and are also absent from the → Hamiltonian function. The generalized → momentum associated with an ignorable coordinate is a → constant of the motion.
→ ignore; → coordinate.
hamârâhâ-ye qotbi (#)
Fr.: coordonnées polaires
A coordinate system in which the position of any point (M) in a plane is specified by two coordinates: 1) ρ, which expresses the distance from a fixed point (the pole, denoted O), and 2) the number φ, which is the angle formed by the line segment OM and a fixed reference line passing through the pole.
→ polar; → coordinate.
Fr.: coordonnées précessées, ~ corrigées de la précession
The apparent position of a celestial object corrected for the epoch → precession.
Precessed, p.p. of → precess; → coordinates.
Fr.: coordonnées de Rindler
The coordinates that describe the → Minkowski space-time in a → hyperbolic version of → polar coordinates. If the coordinates in an → inertial frame is denoted by (t,x), the Rindler coordinates (η,ξ) are defined by: t = (1/α) eαξ sinh (αη) and x = (1/α) eαξ cosh (αη), where α is some positive constant.
Named after Wolfgang Rindler (1924-), Austrian physicist; → coordinates.
Fr.: coordonnées sphériques
A coordinate system using an origin (O) and three perpendicular axes (Ox, Oy, Oz), in which the position of a point (P) is given by three numbers (r, θ, φ). The coordinate r is the distance from the origin, θ the angle between the z-axis and the r direction, and φ the angle between the projection of r on the xy-plane and the Ox-axis. The coordinate φ is also called the → azimuthal angle.
→ spherical; → coordinate.
spherical polar coordinate
hamârâhâ-ye kore-yi-ye qotbi
Fr.: coordonnées sphériques polaires
Same as → spherical coordinates.
→ spherical; → polar; → coordinate
supergalactic coordinate system
râžmân-e hamârâhâ-ye abarkahkašâni
Fr.: système des coordonnées supergalactiques
A spherical → coordinate system in which the → equator is the → supergalactic plane. Supergalactic longitude, SGL, is measured → counterclockwise from direction l = 137.37 deg, b = 0 deg (between 0 and 360 deg). The zero point for supergalactic longitude is defined by the intersection of this plane with the → Galactic plane. In the → equatorial coordinate system (J2000) this is approximately 2.82 h, +59.5 deg. Supergalactic latitude, SGB, is measured from the supergalactic plane, positive northward and negative southward. The North Supergalactic Pole (SGB=90 deg) lies at galactic coordinates l = 47.37 deg, b = +6.32 degrees, corresponding to the equatorial coordinate system (J2000) 18.9 h, +15.7 deg.
→ supergalactic; → coordinate; → system.
Fr.: coordonées topocentriques
A coordinate system that uses the observer's location as its central reference point. Usually, the difference in the position of an object in the sky measured using topocentric and geocentric coordinates is very small because most celestial objects are so far away. However, for nearby objects this is not true. The Sun, for example, may appear displaced as much as eight arcseconds from its geocentric position, and the Moon by as much as one degree.
Topocentric, from topo- combining form of Gk. topos "place" + centric, from → center; → coordinate.
Hamârâhâ, → coordinate; jâ-markazi "topocentric," from jâ "place" (from Mid.Pers. giyâg "place;" O.Pers. ā-vahana- "place, village;" Av. vah- "to dwell, stay," vanhaiti "he dwells, stays;" Skt. vásati "he dwells;" Gk. aesa (nukta) "to pass (the night);" Ossetic wat "room; bed; place;" Tokharian B wäs- "to stay, wait;" PIE base ues- "to stay, live, spend the night") + markazi, of, pertaining to markaz, → center.
Universal Time Coordinated
zamân-e jahâni-ye hamrâyânidé
Fr.: temps universel coordonné
Sale as → Coordinated Universal Time (UTC).