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

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 → 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.

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.

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.

Math.: In plane Cartesian coordinates, the distance of a point from the x-axis measured parallel to the y-axis. → abscissa.

Ordinate, from N.L. (linea) ordinate (applicata) "(line applied) in order;" from ordinatus "arranged."

Ârâ, from ârâstan "to arrange, to set in order, adorn," Mid.Pers. ârây-, ârâstan "to arrange, adorn;" O.Pers. rās- "to be right, straight, true," rāsta- "straight, true" (Mod.Pers. râst "straight, true"), rād- "to prepare;" Av. rāz- "to direct, put in line, set," 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."

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.

Same as → spherical coordinates.

→ spherical; → polar; → coordinate

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.

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.

Sale as → Coordinated Universal Time (UTC).

→ Coordinated Universal Time (UTC).