Seonglae ChoInternational Celestial Reference System
International Celestial Reference System (ICRS)
The International Celestial Reference System (ICRS) is the fundamental celestial reference system adopted by the International Astronomical Union (IAU) for high-precision positional astronomy. The ICRS, with its origin at the solar system barycenter and space fixed axis directions, is meant to represent the most appropriate coordinate system for expressing reference data on the positions and motions of celestial objects.
https://aa.usno.navy.mil/faq/ICRS_doc
International Celestial Reference System and its realizations
The International Celestial Reference System (ICRS) is the current standard celestial reference system adopted by the International Astronomical Union (IAU). Its origin is at the barycenter of the Solar System, with axes that are intended to "show no global rotation with respect to a set of distant extragalactic objects".[1][2] This fixed reference system differs from previous reference systems, which had been based on Catalogues of Fundamental Stars that had published the positions of stars based on direct "observations of [their] equatorial coordinates, right ascension and declination"[3] and had adopted as "privileged axes ... the mean equator and the dynamical equinox" at a particular date and time.[4]
https://en.wikipedia.org/wiki/International_Celestial_Reference_System_and_its_realizations