IAU Symposium 401

Advancing Reference Systems, Ephemeris, and Standards

From the Earth and the Moon to Solar System Bodies

04 to 09 August, 2025 | La Plata, Buenos Aires, Argentina

Programme

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

SESSION 1:

Earth rotation models and Earth Orientation Parameters (EOP)

It will expand on the determination, analysis, and prediction of EOP, addressing corrections to precession-nutation, polar motion, and values of UT1-UTC, including their derivation from combined observational techniques. EOP geophysical modeling, excitation, and forecast.

Key topics will cover:

  • Precession and nutation theories
  • Inconsistencies and updates to IAU2000/IAU2006 precession-nutation
  • Determination and analysis of EOP series
  • Geophysical modeling, excitation, and climate variability of EOP
  • Predictions of EOP

Chairs: Jolanta Nastula (PL), Cheng-Li Huang (CN), Alberto Escapa (SP)

Invited speakers: Christian Bizouard (FR); José M. Ferrándiz (SP); Justyna Śliwińska (PL); Pengshuo Duan (CN)

SESSION 2:

Celestial and terrestrial reference systems/frames and their observation

It will focus on the current realizations of the ICRS/ITRS as well as their future developments, paying attention to their consistent realization with EOP. It will also address observing techniques, emphasizing VLBI and new emerging concepts.

 Key topics will cover:

  • Model choices and combination strategies in ICRF and ITRF realizations
  • Limitations of ICRF3 and ITRF2020 and perspectives
  • Next generation of ICRS and ITRS and their realization
  • Multi-technique CRF-TRF solutions together with EOP
  • Future development of VLBI and other observing techniques for Earth rotation studies and reference frames

Chairs: Oleg Titov (AU), Manuela Seitz (DE), Laura Fernández (AR)

Invited speakers: Aletha de Witt (ZA); Xavier Collilieux (FR); Lucia McCallum (AU)

SESSION 3:

Reference systems/frames for the Moon and other solar system bodies and measuring systems

It focuses on reference frames, rotational elements, and cartographic coordinates of planets, satellites, asteroids, and comets of the solar system. It will also address their rotation, as well as measuring systems.

Key topics will cover:

  • Definition and maintenance of reference systems/frames for solar system bodies and their rotational elements
  • Rotation of the Moon and other solar system bodies
  • Observational techniques for determining the orbital and rotational motions of the Moon
  • Emerging measuring systems and projects

Chairs: Agnès Fienga (FR), Flora Paganelli (FR)

Invited speakers: Brent A. Archinal (US); Nicolas Rambaux (FR); Sergei Klioner (DE); Luca Porcelli (IT)

SESSION 4:

Time scales and time metrology

It will focus on time metrology standards addressing time scales, time dissemination, and timekeeping. Emphasis will be put on future challenges with impact on astronomy as the realization of a continuous reference time scale, the redefinition of the second and the lunar time.

Key topics will cover:

  • TimeScales
  • Time and Metrology standards
  • Continuous UTC
  • Lunar Time

Chairs: Mizuhiko Hosokawa (JP), Felicitas Arias (FR)

Invited speakers: Joseph Achkar (FR); Tetsuya Ido (JP); Pascale Defraigne (BE)

SESSION 5:

Ephemerides of solar system objects

It will focus on the most recent and accurate measurements and models affecting the orbital dynamics of the solar system bodies, including the planets, planetary satellites, asteroids, comets, and Kuiper Belt objects. Special attention will be given to Near-Earth Objects (NEO) to assess their prediction and reconstruction capability.

Key topics will cover:

  • Orbit prediction and reconstruction of Near-Earth Objects and their populations
  • Observations for developing ephemeris of solar system object
  • Orbits of solar system objects
  • New solar system objects; interstellar, Kuiper-Belt

Chairs: Giovanni B. Valsecchi (IT), Dmitry Pavlov (RU), Ryan S. Park (US)

Invited speakers: Karen Meech (US); Federica Spoto (US); Shantanu Naidu (US); Luke Dones (US)

SESSION 6:

Astronomical standards

It will focus on standards in fundamental astronomy and their potential revision and/or extension to other parameters, including updates of the terminology and lunar standards.

Key topics will cover:

  • Current status of IAU standards
  • Update of astronomical constants & terminology
  • Algorithms and procedures of astronomical standards
  • Lunar standards
  • Standards organizations

Chairs: C. Y. Hohenkerk (UK), Susan G. Stewart (US)

Invited speakers: Antonia J. Wilmot (UK); Sharyl Byram (US); Detlef Angermann (DE)

Round table about the development of International standards services for space and surface navigation in the solar system, cooperation of standards organizations, and Moon standards (B. Archinal, C. Bizouard, C.Y. Hohenkerk, and S. Stewart)