altazimuth coordinate system
râžmân-e hamârâhâ-ye farâzâ-sugân
Fr.: coordonnées azimutales
The coordinate system in which the position of a body on the → celestial sphere is described with respect to an observer's → celestial horizon and → zenith. The coordinates of a point in this system are its → altitude on the → vertical circle, and its → azimuth westward (clockwise) along the celestial horizon from the observer's south. Same as → horizon coordinate system.
hamârâhâ-ye axtaršenâsik, ~ axtarsršnâxti (#)
Fr.: coordonnées astronomiques
Values in a reference system used to relate the position of a body on the celestial sphere.
Barycentric Coordinate Time (TCB)
zamân-e hamârâ-ye gerânigâhi
Fr.: temps-coordonnée barycentrique (TCB)
A → coordinate time having its spatial origin at the solar system barycenter. It is intended to be used as the independent variable of time for all calculations pertaining to orbits of planets, asteroids, comets, and interplanetary spacecraft in the solar system. → Barycentric Dynamical Time (IDB).
Fr.: coordonnées canoniques
Any set of generalized coordinates of a system together with their → conjugate momenta.
Fr.: coordonnées cartésiennes
A → coordinate system in which the position of a point is specified by two (in a plane) or three (in 3-dimensional space) → real numbers representing the distances from two perpendicular axes or from three perpendicular planes, respectively. René Descartes (1596-1650) introduced the coordinates system in his La Géométrie in 1637.
hamârâhâ-ye âsmâni (#)
Fr.: coordonées célestes
Any system of coordinates used to define a point on the celestial sphere (zenith distance, altitude, celestial latitude, celestial longitude, etc.).
Fr.: coordonnées comobiles
A system of coordinates used in cosmology which is fixed with respect to the overall → Hubble flow of the universe. A given galaxy's location in comoving coordinates does not change as the Universe expands.
1) hamârâ (#); 2) hamârâstan
Fr.: 1) coordonnée; 2) coordonner
1) Any of a series of numbers which, in relation to a given
→ frame of reference, locate a point in space. See also:
→ astronomical coordinates→ canonical coordinates→ Cartesian coordinates→ celestial coordinates→ cylindrical coordinates→ equatorial coordinates→ Galactic coordinates→ generalized coordinates→ polar coordinates→ spherical coordinates→ precessed coordinates→ topocentric coordinates.
From L. co- "together," → com- + orinatus, p.p. of ordinare "to put in order, arrange," from ordo "order."
Hamârâ, from ham- "together," → com- + ârâ stem of ârâstan "to arrange, to set in order, adorn," Mid.Pers. ârây-, ârâstan "to arrange, adorn," O.Pers. râs- "to be right, straight, true," râsta- "straight, true" (Mod.Pers. râst "straight, true"), râd- "to prepare," Av. râz- "to direct, put in line, set," Av. razan- "order," Gk. oregein "to stretch out," L. regere "to lead straight, guide, rule," p.p. rectus "right, straight," Skt. rji- "to make straight or right, arrange, decorate," PIE base *reg- "move in a straight line."
Fr.: système de coordonnées
Math: A system for locating each point in space by a set of numbers.
In relativity, the proper time in the specified reference frame. Because of time dilation, this may differ from the time experienced by any participant in the events being considered. It is the time basis (or coordinate) to be used in the theory of motions referred to this system.
Coordinated Universal Time (UTC)
zamân-e jahâni-ye hamrârâsté
Fr.: temps universel coordonné
An international high-precision time standard based on the Greenwich Mean Time and adjusted to compensate for divergence from atomic time. It is based on the non-uniform rotation of the Earth (UT1) and the perfectly uniform international atomic time (TAI). UTC differs from TAI by the total number of → leap seconds, so that UT1-UTC stays smaller than 0.9 sec in absolute value.
hamârâ-ye nâdidé engâshté
Fr.: coordonnée ignorée
Same as → ignorable coordinate.
hamârâhâ-ye ostovâne-yi (#)
Fr.: coordonnées cylindriques
A coordinate system for a point in space, using an origin (O) and three perpendicular axes (Ox, Oy, Oz), in which a point (P) in space is specified by three numbers ρ, φ, z. The two first numbers, ρ and φ, are → polar coordinates for the vertical projection of P on the xy-plane, and z is the vertical distance of P from the xy-plane.
equatorial coordinate system
râžmân-e hamârâhâ-ye hamugâri
Fr.: système de coordonnées équatoriales
An astronomical → coordinate system for indicating the positions of → celestial objects on the → celestial sphere. The system consists of two components, → right ascension and → declination. Right ascension is the angle between the → vernal equinox and the point where the → hour circle intersects the → celestial equator. The right ascension is always measured eastward from the vernal equinox, in the units of hours, minutes, and seconds. Declination is the angle between the celestial equator and the position of the star measured along the star's hour circle. It is measured in degrees, minutes, and seconds north or south of the celestial equator. By definition, the vernal equinox is located at right ascension 0h and declination 0°. Equatorial coordinates change with time due to the → precession of the Earth's → rotation axis.
Fr.: coordonnées équatoriales
Celestial coordinates in the → equator system.
Fr.: coordonnées galactiques
A system of astronomical coordinates using → latitude (bII) measured north and south from the → Galactic equator and → longitude (lII), measured from the → Galactic Center in the sense of increasing → right ascension from 0 to 360 degrees. In the old system (lI,bI), the Galactic center was at lI = 327°41'. Same as → galactic system.
GCN: The Gamma-ray Coordinates Network
turbast-e hamârâhâ-ye partowhâ-ye gâmâ
Fr.: Le réseau des coordonnées des rayons gamma
A follow-up community network concerned with → gamma-ray burst (GRB)s. It deals with: 1) locations of GRBs and other → transients detected by spacecraft (most in real-time while the GRB is still bursting), and 2) reports of follow-up observations (the Circulars) made by ground-based and space-based optical, radio, X-ray, TeV, and other observers. The GCN Circulars allow the GRB follow-up community to make optimum use of its limited resources (labor and telescope time) by communicating what has already been done or will soon be done.
Fr.: coordonnées généralisées
In a material system, the independent parameters which completely specify the configuration of the system, i.e. the position of its particles with respect to the frame of reference. Usually each coordinate is designated by the letter q with a numerical subscript. A set of generalized coordinates would be written as q1, q2, ..., qn. Thus a particle moving in a plane may be described by two coordinates q1, q2, which may in special cases be the → Cartesian coordinates x, y, or the → polar coordinates r, θ, or any other suitable pair of coordinates. A particle moving in a space is located by three coordinates, which may be Cartesian coordinates x, y, z, or → spherical coordinates r, θ, φ, or in general q1, q2, q3. The generalized coordinates are normally a "minimal set" of coordinates. For example, in Cartesian coordinates the simple pendulum requires two coordinates (x and y), but in polar coordinates only one coordinate (θ) is required. So θ is the appropriate generalized coordinate for the pendulum problem.
geocentric coordinate system
râžmân-e hamârâhâ-ye zamin-markazi
Fr.: système de coordonnées géocentriques
A coordinate system which has as its origin the center of the Earth.
Geocentric Coordinate Time (TCG)
zamân-e hamârâ-ye zamin-markazi
Fr.: Temps coordonné géocentrique
The proper time experienced by a clock at rest in a coordinate frame co-moving with the center of the Earth, i.e. a clock that performs exactly the same movements as the Earth but is outside the Earth's gravity well. TCG was defined in 1991 by the International Astronomical Union as one of the replacements for Barycentric Dynamical Time (TDB).