Calendar of Events

It is our pleasure to announce that the International Astronomical Union (IAU) Symposium
“Advancing Reference Systems, Ephemeris, and Standards: from the Earth and the Moon
to Solar System Bodies” (IAUS 401) will be held from August 4 to 9, 2025, at the National
University of La Plata (UNLP), La Plata (Argentina).

Reference systems and their standardization are of paramount importance to many fields
of astronomy. Some examples are the reduction of ground-based observations, space
astrometry, astrophysics missions, and space missions to solar system planetary bodies
and beyond. The concept of a reference system and its realization requires the
convergence of reference frames, ephemeris, and time scales to be developed respecting
associated standards, thus fulfilling one of the IAU strategic goals as the provider of
astronomical standards and their use.
The IAUS 401 will provide a forum to discuss the latest results and prospects in these
fields and thus facilitate the coordination of common standards across agencies and
organizations.

The IAUS 401 is structured in six key topics:
1.- Earth rotation models and Earth Orientation Parameters (EOP)
2.- Celestial and terrestrial reference systems/frames
3.- Reference systems/frames for the Moon and other solar system bodies
4.- Time scales and time metrology
5.- Ephemerides of solar system objects
6.- Astronomical standards

The IAUS 401 registration, abstract submission, and IAU travel grant applications are
already open. The symposium will be in a hybrid format to welcome in-person and online
participation.

For additional information and contact details, please refer to IAUS 401 website:
https://iaus401.fcaglp.unlp.edu.ar/

We are looking forward to seeing you in La Plata!
Sincerely,

Alberto Escapa and Laura I. Fernández,
On behalf of the SOC and the LOC