International Celestial Reference Frame
Encyclopedia
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. Note that, in astrometry
, a reference frame is the physical realization of a reference system, i.e., the 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.
Barycentric coordinates (astronomy)
In astronomy, barycentric coordinates are non-rotating coordinates with origin at the center of mass of two or more bodies.The barycenter is the point between two objects where they balance each other. For example, it is the center of mass where two or more celestial bodies orbit each other...
of the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
, defined by the measured positions of 212 extragalactic sources (mainly quasars). Although relativity
Special relativity
Special relativity is the physical theory of measurement in an inertial frame of reference proposed in 1905 by Albert Einstein in the paper "On the Electrodynamics of Moving Bodies".It generalizes Galileo's...
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
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
) and other astronomical objects. Note that, in astrometry
Astrometry
Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. The information obtained by astrometric measurements provides information on the kinematics and physical origin of our Solar System and our Galaxy, the Milky...
, a reference frame is the physical realization of a reference system, i.e., the coordinates of datum points. The ICRF is the realization of the International Celestial Reference System
International Celestial Reference System
The International Celestial Reference System is the current standard celestial reference system adopted by the International Astronomical Union . Its origin is at the barycenter of the solar system, with axes that are intended to be "fixed" with respect to space...
, and agrees with the orientation of the Fifth Fundamental Catalog (FK5) "J2000.0" frame to within the (lower) precision of the latter.