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Reference.org
Barycentric and geocentric celestial reference systems
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<p>The barycentric celestial reference system (BCRS) is a coordinate system used in <a href="/facts/Astrometry/9ycEEAvD">astrometry</a> to specify the location and motions of astronomical objects. Its center of coordinates as the center of mass of the entire Solar System, its <a href="/facts/Barycenter/Fw9renao">barycenter</a>. It was created in 2000 by the <a href="/facts/International_Astronomical_Union/GMFPImXo">International Astronomical Union</a> (IAU) to be the global standard reference system for objects located outside the gravitational vicinity of <a href="/facts/Earth/HLLmDfj0">Earth</a>: planets, moons, and other Solar System bodies, stars and other objects in the <a href="/facts/Milky_Way/ulF6lccN">Milky Way</a> galaxy, and extra-galactic objects. </p><p>The geocentric celestial reference system (GCRS), also created by the IAU in 2000, is a similar standard coordinate system used to specify the location and motions of <a href="/facts/Near-Earth_objects/UwnPRnSN">near-Earth objects</a>, such as satellites. Its center of coordinates is the center of mass of the Earth. </p><p>These systems make it easier for scientists and engineers to compile, share, compare, and convert accurate measurements worldwide, by establishing standards both of measure and of methodology, and providing a consistent framework of operations. The focus of the BCRS is on astronomy: exploration of the <a href="/facts/Solar_System/QIcLSazQ">Solar System</a> and the universe. The BCRS is the system currently used for expressing positional data in astronomical references, such as the <a href="/facts/Hipparcos_Catalogue/Th2HW7VN">Hipparcos star catalog</a>. </p><p>The focus of the GCRS is somewhat more on the navigation of Earth satellites and the geophysical applications they support. The proper functioning of the <a href="/facts/Global_Positioning_System/DKVLnzF3">Global Positioning System</a> (GPS) is directly dependent upon the accuracy of satellite measurements as supported by the GCRS. </p>