An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

Values in a reference system used to relate the position of a body on the celestial sphere.

→ astronomical; → coordinates.

Any set of generalized coordinates of a system together with their → conjugate momenta.

→ canonical; → coordinates.

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.

→ Cartesian; → coordinate.

Any system of coordinates used to define a point on the celestial sphere (zenith distance, altitude, celestial latitude, celestial longitude, etc.).

→ celestial; → coordinates.

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.

→ comoving; → frame.

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.

→ cylindrical; → coordinate.

Celestial coordinates in the → equator system.

→ equatorial, → coordinate.

A system of astronomical coordinates using → latitude (b^II) measured north and south from the → Galactic equator and → longitude (l^II), measured from the → Galactic Center in the sense of increasing → right ascension from 0 to 360 degrees. In the old system (l^I,b^I), the Galactic center was at l^I = 327°41'. Same as → galactic system.

→ galactic; → coordinate.

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.

→ gamma ray; → coordinate; → network.

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, ..., q_n. 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.

→ generalized; → coordinate.

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.

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.

The apparent position of a celestial object corrected for the epoch → precession.

Precessed, p.p. of → precess; → coordinates.

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) e^αξ sinh (αη) and x = (1/α) e^αξ cosh (αη), where α is some positive constant.

Named after Wolfgang Rindler (1924-), Austrian physicist; → coordinates.

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.

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.