DivA: Fundamental Astronomy

Gaia's Sky in Colour

Gaia’s all-sky view of the Milky Way and neighbouring galaxies, based on measurements of nearly 1.7 billion stars. (ESA / Gaia / DPAC)

Gaia Spacecraft Illustration

An artist’s impression of the Gaia spacecraft. (ESA / ATG Medialab)

IAU Division A gathers astronomers studying a wide range of problems related to fundamental physical phenomena, such as time, inertial reference frames, positions and proper motions of celestial objects and the precise dynamical computation of motions of celestial bodies in planetary, stellar and galactic systems. It is always concerned with the same basic problems, but the solutions are constantly being reconsidered and revised thanks to new observational data.

While this work may not seem particularly spectacular or newsworthy, it plays a fundamental contribution to astronomy — and it is often extremely challenging. The collection of new observations, improvements in standards, revisions of existing models and huge theoretical and computational simulations are only possible with an interdisciplinary approach and the collaboration of other IAU Divisions.

For Division A, the most spectacular and popular astrometry mission is certainly Gaia, involving a huge international team. But let’s not forget JASMINE (Japan Astrometry Satellite Mission for Infrared Exploration) and some other exciting missions in the works.

The observational activity of Division A is not limited to space missions; it also involves traditional ground-based observations, using telescopes and cameras that just keep getting better. Optical, infrared, and radio astrometry campaigns and systematic surveys are developed every year and contribute substantially to the flood of new ground-based data.

Besides collecting observations, Division A also develops models and theories and performs numerical simulations necessary to interpret data, improve our knowledge and to understand unexpected findings.

EPIC image of Earth

Understanding the Universe begins with understanding our home planet, Earth — in particular, its rotation, which carries astronomers’ ground-based telescopes around with it. This image was captured on 31 July 2018 by the Earth Polychromatic Imaging Camera (EPIC) aboard the Deep Space Climate Observatory (DSCOVR) spacecraft. (NASA EPIC Team)

exoplanet KOI-872b

Slight variations in the times of transit of exoplanet KOI-872b in front of its host star enabled celestial dynamicists to infer the existence of a second planet in the system. (David Nesvorny et al., Science, 1 June 2012)

Organisation of Division A

Division A coordinates a wide range of scientific activity, mainly performed within the five Commissions:

Division A also hosts eight functional (permanent) Working Groups:

All Division A Commissions and Working Groups have excellent Organising Committees and show, through their annual and triennial reports, their strong scientific activity and investment in modern astronomy.

General Assembly Scientific Programme for Division A

The scientific community, both within and beyond the membership of Division A, are invited to Symposium 348, 21st Century Astrometry: Crossing the Dark and Habitable Frontiers at the GA (28–31 August). Its challenge is to connect precisely all of the new celestial and terrestrial reference frames relevant to improving our understanding of Earth’s rotation. A new astrometry framework has to be designed that combines past and future data.

VLA Rainbow

Radio interferometry, done with widely separated telescopes, such as those of the Very Large Array in New Mexico, US, has enabled the measurement of proper motions for stars and galaxies. Such observations are key to establishing celestial reference frames. (NRAO / AUI / NSF)

Division A will devote the scientific content of our Division Meeting to the topics covered by the two other proposals originally submitted for the GA. On 27 August we will welcome two sessions: one about the space mission Gaia and another about reference frames. Both sessions will feature experts in the fields: T. Prusti, A. Brown, L. Lindegren, P. Tanga and A. Vallenari for Gaia, and P. Charlot, F. Mignard, Z. Altamimi and R. Heinkelmann for reference frames. We’ll have a large common poster session associated with the talks.

A third topic was also proposed, concerning the dynamics of small bodies in the Solar System and in exoplanetary systems, in the framework of new models in celestial mechanics. However, rather than organising parallel and redundant sessions, Division A decided to join Division F on 24 August for a joint Planet Days session, with speakers representing both Divisions.

As a sign of the dynamism of Division A, almost all our Commissions and Working Groups will hold business meetings during the General Assembly. These are concentrated during the second week (27‒29 August), in parallel with Symposium 348, to allow maximum participation. Furthermore, the idea of a PhD prize to motivate young scientists to participate in IAU meetings and other Union activities was well received by Division A, and our first PhD prize, for 2017, goes to Gisela Ortiz Leon for her work on ultra-high-precision astrometry with centimetre- and millimetre-wavelength very-long-baseline interferometry. The prize will be presented to the laureate on 27 August, at the end of the scientific session.

ANNE LEMAÎTRE conducts research in celestial mechanics at the University of Namur, Belgium, where she is a professor in the Department of Mathematics and at the research institute naXys (Namur Institute for Complex Systems) as well as Dean of the Faculty of Sciences.