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 can avoid producing incompatible results merely from using different measures of its radius. The IAU famously redefined the definition of planet in a way that relegated Pluto to be a dwarf planet.
Among IAU's activities has been dissemination of alerts (by mail) on recent astronomical phenomena, IAU Circulars (IAUC), first mailed in 1920 and still being mailed through 2016.