CRF – Celetial Reference Frame

A Celestial Reference Frame defines a coordinate system for positions of astronomical objects outside Earth, serving as the fundamental reference for Earth orientation and space navigation. It is realized by VLBI observations of distant quasars, whose positions are considered fixed at cosmic scales. The latest realization, ICRF3, provides microarcsecond-level accuracy and serves as the celestial counterpart to the terrestrial frame. Earlier realizations such as ICRF1 and ICRF2 form part of a continuous improvement in precision and stability, ensuring alignment with the ITRF through Earth Orientation Parameters.