A3 – Commission A3 Fundamental Standards


The purpose of IAU Commission C.A3 - Fundamental Standards is to facilitate advances in astronomy, and other fields in science an engineering, by developing, implementing, and communicating fundamental IAU-endorsed standards for fundamental astronomy. Such standards include, but are not limited to:

  • celestial & terrestrial reference systems/frames and the transformations among them;
  • time scales;
  • precession-nutation models;
  • Earth rotation and polar motion, including physical models (e.g., Earth's gravity field, lunar gravity field, Earth interior model, solid Earth-tide modelling); star catalogues;
  • ephemerides of solar system bodies; special and general relativistic models for time and space.

    This involves:

    1. producing robust standards, and ensuring that new standards are readily understood by both the astronomical and broader scientific communities; i.e., are relevant and "fit for purpose";
    2. ensuring that the associated nomenclature is well defined and understood; encouraging future research, particularly groups with the appropriate expertise, to improve their models and help them to develop relevant standards;
    3. implementing good practices in setting and using IAU standards, including identifying requirements for new standards; providing a link between the users of fundamental standards and developers to (1) inform users of current standards and the status of those under development, and (2) to accept input from the broader user community in order to ensure that standards are relevant for practical needs; and
    4. encouraging interest among young astronomers in developing the field of astronomical standards and services for the scientific community.
    FS will serve as the primary point of contact between Division A and the user community regarding standards for fundamental astronomy.

    Join FS & help make standards easy for everyone.


    Send comments, questions, suggestions to the President of Commission A3.

    Work for the next 6 - 9 years:

    1. Maintain and enhance existing links between the IAU, the IERS, the IAG's GGOS, CCTF, and others;
    2. coordinate and promote the continued good work of SOFA, the WGNSFA, and the WGCCRE;
    3. develop, implement, and disseminate new standards currently under consideration and development within Div. A; e.g., ICRS3, precession-nutation models, and relativistic VLBI standards;
    4. develop a Web presence for communication and coordination that will both inform users about status of new and emerging standards, and provide a means for the user community to provide feedback on standards;
    5. ensure that user feedback on fundamental standards is shared with scientists who are developing new standards within the IAU framework; actively develop new and improved standards and services to meet emerging needs;
    6. promote and encourage interest among young astronomers in developing the field of astronomical standards and services for the scientific community.



  • Commission Web Page

    Commission Members (104)

    Under Division

    Division A Fundamental Astronomy

    James Lindsay Hilton

    US Naval Observatory
    Astronomical Applications Dept
    1274 Hwy 238
    Jacksonville OR 97530
    Oregon (OR)
    United States

    Phone: +1 541 324 9432
    Email 1: jameslhilton1navymil
    Email 2: jmslhiltongmailcom
    Organization website: http://www.usno.navy.mil/

    NCA adherence: United States

    Last updated:
    September 6, 2018

    Susan Gessner Stewart

    United States Naval Observatory
    Astronomical Applications
    3450 Massachusetts Ave., NW
    Washington 20392-5420
    United States

    Phone: +1 615 343 4647
    Email 1: susangstewartnavymil
    Email 2: susangstewartvanderbiltedu
    Personal website: https://my.vanderbilt.edu/susanstewart/
    Organization website: http://www.usno.navy.mil/USNO/astronomical-applications

    NCA adherence: United States

    Last updated:
    October 10, 2018

    Catherine Y. Hohenkerk

    HM Nautical Almanac Office
    United Kingdom

    Phone: +44 07854 706558
    Email: catherinehohenkerkgmailcom

    NCA adherence: United Kingdom

    Last updated:
    November 9, 2018

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