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:
“The mistake that men make is that they do not believe in theater. Otherwise, they would know that every man is allowed to play the celestial tragedies and to become god. All he has to do is harden his heart.”
—Albert Camus (1913–1960)
“If we define a sign as an exact reference, it must include symbol because a symbol is an exact reference too. The difference seems to be that a sign is an exact reference to something definite and a symbol an exact reference to something indefinite.”
—William York Tindall (1903–1981)
“It would be nice to travel if you knew where you were going and where you would live at the end or do we ever know, do we ever live where we live, we’re always in other places, lost, like sheep.”
—Janet Frame (b. 1924)