The International Astronomical Union (IAU or UAI) is an association of professional astronomers. Among their activities are standardizing the designations of bodies and standardizing recommended values of measurable quantities, e.g., the radius of the Sun. As such, it assists communication and collaboration among researchers regarding observation data, modeling, etc. Thus, for example, two researchers each modeling the Sun would not find divergence merely from using different measures of its radius.
Celestial Coordinate System
Galactic Coordinate System (GCS)
International Celestial Reference System (ICRS)
Minor Planet Center (MPC)
Terrestrial Time (TT)