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.”
—Michel de Montaigne (1533–1592)
“In sum, all actions and habits are to be esteemed good or evil by their causes and usefulness in reference to the commonwealth, and not by their mediocrity, nor by their being commended. For several men praise several customs, and, contrarily, what one calls vice, another calls virtue, as their present affections lead them.”
—Thomas Hobbes (1579–1688)
“Faith, I have been a truant in the law,
And never yet could frame my will to it,
And therefore frame the law unto my will.”
—William Shakespeare (1564–1616)