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.
Fr.: système de coordonnées
Math: A system for locating each point in space by a set of numbers.
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.
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.
geographic coordinate system
râžmân-e hamârâhâ-ye zaminnegârik
Fr.: système de coordonnées géographiques
horizon coordinate system
râžmân-e hamârâhâ-ye ofoqi
Fr.: coordonnées horizontales
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.