A1 – Commission A1 Astrometry


The Commission A1 'Astrometry' coordinates research related to the celestial coordinate system (definition, realization, and maintenance) as well as positions, proper motions and parallaxes (distances) of celestial objects. It is also involved in the accurate determination of distances which is one of the most fundamental and important tasks of astrometry, forming the basis for astrophysical science.

Moreover the Commission A1 coordinates ground and space-based observing astrometric programs, and promotes education in astrometry. It spans a vast range of objects from the Earth-Moon system to quasars at cosmological distances, as well as a large range of techniques with the common goal of enhancing our understanding of motions of celestial objects and their measurement in coordinate systems.

Over the coming years Commission A1 will focus on supporting the following particularly important activities:

  • The construction of the ICRF3, the next version of the radio VLBI-based reference frame, which is the realization of the celestial coordinate system.
  • The ESA Gaia space mission, launched in Dec 2013, which will provide the next generation optical celestial reference frame. In particular Commission A1 will support the coordination of research to provide a solid link of this last frame to the ICRF3
  • The support of space and ground-based programs at various wavelengths, like LSST and others to densify the celestial coordinate system toward fainter magnitudes (fluxes). An important task will be to observe motions of targets fainter than those included in the primary frames (ICRF3, Gaia) or to observe any celestial object at various epochs.
  • Link:

    Commission Members (194)

    Under Division

    Division A Fundamental Astronomy

    Anthony G.A. Brown

    Leiden University
    Leiden Observatory
    PO Box 9513
    2300 RA Leiden

    Phone: +31 71 527 58 84
    Fax: +31 71 527 57 43
    Email: brownstrwleidenunivnl
    Personal website: http://www.strw.leidenuniv.nl/~brown
    Organization website: http://www.strw.leidenuniv.nl/

    Last updated:
    December 6, 2017

    Jean Souchay

    Observatoire de Paris
    61 Av de l'Observatoire
    75014 Paris

    Phone: +33 1 40 51 23 22
    Fax: +33 1 40 51 22 91
    Email: jeansouchayobspmfr
    Organization website: http://syrte.obspm.fr/

    Last updated:
    December 6, 2017

    Dafydd Wyn Evans

    University of Cambridge
    Institute of Astronomy
    Madingley Road
    Cambridge CB3 0HA
    United Kingdom

    Phone: +44 1223 764608
    Fax: +44 1223 337523
    Email: dweastcamacuk
    Personal website: http://www.ast.cam.ac.uk/~dwe
    Organization website: http://www.ast.cam.ac.uk/

    Last updated:
    December 6, 2017

    Organizing Committee

    Search Scientific Bodies


    IAU General Assembly 2018

    IAU XXX GA Vienna Logo


    How to Become a Member

    CAPjournal issue 22 now available

    CAPjournal issue 22

    IAU Office of Astronomy for Development

    Office for Astronomy Development

    Astronomy for Development 
    Strategic Plan 2010–2020

    Strategic Plan

    Symposia and Meetings


    IAU Office for Astronomy Outreach

    Office for Astronomy Outreach

    IAU Office for Young Astronomers

    Office for Young Astronomers

    International School for Young Astronomers

    International School for Young Astronomers

    Astronomy Outreach Newsletters and Events

    Outreach Newsletters

    IAU e-Newsletter
    Volume 2017 n° 6

    Latest e-Newsletter

    Subscribe to the e-Newsletter


    UNESCO-IAU Portal to the Heritage of Astronomy