The International Celestial Reference Frame (ICRF) is a quasi-inertial reference frame centered at the barycenter of the Solar System, defined by the measured positions of 212 extragalactic sources (mainly quasars). Although relativity implies that there is no true inertial frame, the extragalactic sources used to define the ICRF are so far away that any angular motion is essentially zero. The ICRF is now the standard reference frame used to define the positions of the planets (including the Earth) and other astronomical objects. It has been adopted by International Astromical Union since 1st January 1998.
Note that, in astrometry, a reference frame is the physical realization of a reference system, i.e., the reference frame is the reported coordinates of datum points. The ICRF is the realization of the International Celestial Reference System, and agrees with the orientation of the Fifth Fundamental Catalog (FK5) "J2000.0" frame to within the (lower) precision of the latter.
Famous quotes containing the words celestial, reference and/or frame:
“Man will rise, if God by exception lends him a hand; he will rise by abandoning and renouncing his own means, and letting himself be raised and uplifted by purely celestial means.”
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—For the State of New Jersey, U.S. public relief program (1935-1943)