The International Astronomical Union (IAU or UAI) is an
association of professional astronomers, which takes initiatives to
promote cooperation in astronomical science, among them,
standardizing the designations of bodies and
standardizing recommended (i.e., nominal) values of measurable quantities,
e.g., the radius of the Sun.
This assists communication and collaboration among researchers regarding
observation data, modeling, etc. Thus, for example, two researchers
each modeling the Sun can avoid results incompatible solely
because they selected different determinations of its radius.
The IAU famously refined their definition of planet such that
Pluto was relegated to the status of "dwarf planet".
Also among IAU's activities has been dissemination of alerts on
recent astronomical phenomena:
from 1920 through 2017, the IAU Circulars (IAUC)
were sent by mail,
and since 2002, similar alerts have been sent electronically.