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In astronomy, the geocentric model (also known as geocentrism, often exemplified specifically by the Ptolemaic system) is a superseded description of the Universe with Earth at the center. Under most geocentric models, the Sun , Moon , stars , and planets all orbit Earth.
The Earth-centered, Earth-fixed coordinate system (acronym ECEF), also known as the geocentric coordinate system, is a cartesian spatial reference system that represents locations in the vicinity of the Earth (including its surface, interior, atmosphere, and surrounding outer space) as X, Y, and Z measurements from its center of mass.
English: The Ptolemaic geocentric model of the Universe according to the Portuguese cosmographer and cartographer Bartolomeu Velho (Bibliothèque Nationale de France, Paris). Español : El modelo geocéntrico del universo de Ptolomeo , de acuerdo al cosmógrafo y cartógrafo portugués Bartolomeu Velho (Biblioteca Nacional de Francia, París).
In the geocentric equatorial frame, the x, y and z axes are often designated I, J and K, respectively, or the frame's basis is specified by the unit vectors Î, Ĵ and K̂. The Geocentric Celestial Reference Frame (GCRF) is the geocentric equivalent of the International Celestial Reference Frame (ICRF).
A geodetic datum or geodetic system (also: geodetic reference datum, geodetic reference system, or geodetic reference frame, or terrestrial reference frame) is a global datum reference or reference frame for unambiguously representing the position of locations on Earth by means of either geodetic coordinates (and related vertical coordinates) or geocentric coordinates. [1]
Ecliptic longitude or celestial longitude (symbols: heliocentric l, geocentric λ) measures the angular distance of an object along the ecliptic from the primary direction. Like right ascension in the equatorial coordinate system , the primary direction (0° ecliptic longitude) points from the Earth towards the Sun at the March equinox .
Geodetic latitude and geocentric latitude have different definitions. Geodetic latitude is defined as the angle between the equatorial plane and the surface normal at a point on the ellipsoid, whereas geocentric latitude is defined as the angle between the equatorial plane and a radial line connecting the centre of the ellipsoid to a point on the surface (see figure).
Line art drawing of Ptolemaic system. The prevailing astronomical model of the cosmos in Europe in the 1,400 years leading up to the 16th century was the Ptolemaic System, a geocentric model created by the Roman citizen Claudius Ptolemy in his Almagest, dating from about 150 CE.