International Astronomical Union

The International Astronomical Union (IAU), known in French as Union Astronomique Internationale (UAI), is an international non-governmental organisation dedicated to the advancement of astronomy in all its scientific, educational, and developmental dimensions. Founded on 28 July 1919 in Brussels, and headquartered in Paris, the IAU serves as the principal global body uniting professional astronomers and coordinating international efforts in astronomical research, standardisation, and public engagement. With national membership drawn from scientific academies and associations, and individual membership comprising professional astronomers from across the world, the Union plays a central role in defining astronomical nomenclature, fostering scientific cooperation, and promoting the study of the universe.

Functions and Purpose

The IAU is the recognised international authority responsible for assigning names and designations to astronomical objects and their surface features. These include stars, planets, minor planets, and a wide range of celestial bodies. In addition to its nomenclature responsibilities, the Union oversees and promotes professional standards in astronomical research and education.
Its mission encompasses:

• Encouraging global cooperation in astronomical science.
• Supporting professional astronomers at the doctoral level and higher.
• Organising conferences, symposia, and its triannual General Assembly.
• Coordinating educational and outreach initiatives, often in collaboration with international partners such as UNESCO.
• Maintaining systems for astronomical communication, including the distribution of astronomical telegrams through the Central Bureau for Astronomical Telegrams.
• Operating the Minor Planet Center, which acts as the clearinghouse for information relating to minor bodies in the Solar System.

The Union maintains a broad network of working groups and committees that cover topics from planetary nomenclature to star names, ensuring coherent and standardised astronomical practices worldwide.

Historical Development

The IAU was established at the Constitutive Assembly of the International Research Council in Brussels shortly after the First World War. International scientific cooperation, already strong in areas such as stellar cataloguing and solar research, provided the foundation for the Union’s creation. The original seven member states were Belgium, Canada, France, Great Britain, Greece, Japan, and the United States; Italy and Mexico joined soon afterwards.
The first Executive Committee included Benjamin Baillaud as President and Alfred Fowler as General Secretary. The 32 initial Commissions of the Union focused on topics ranging from relativity and celestial mechanics to minor planets, forming the core structure of the first General Assembly held in Rome in 1922. By the close of this Assembly, ten additional nations had joined, bringing the total to nineteen.
Throughout its first fifty years, the Union recorded significant growth and evolution, with detailed accounts preserved in historical bulletins and recollections by past Presidents and General Secretaries. The IAU has continued to adapt to the changing landscape of international astronomy, expanding its programmes and responding to developments in scientific research, technology, and global cooperation.
In recent years, the Union has become known for initiatives such as the NameExoWorlds public naming contests (held in 2015 and 2019), and for its emerging role in shaping policy concerning lunar resources through partnership with the United Nations from 2024.

Membership and Governance

As of August 2019, the IAU comprised 13,701 individual members—professional astronomers from 102 nations. The membership demographics included 18.3 per cent women. The Union’s 82 national members include major scientific bodies such as:

• The Australian Academy of Science
• The Chinese Astronomical Society
• The Indian National Science Academy
• The National Academies (United States)
• The Royal Astronomical Society (United Kingdom)
• The Royal Swedish Academy of Sciences
• The Russian Academy of Sciences
• The Science Council of Japan
• The National Research Foundation of South Africa
• The National Scientific and Technical Research Council of Argentina

The General Assembly, encompassing all members, is the Union’s sovereign decision-making body. It determines policy, approves statutes and by-laws, and elects key committees. Voting rules differ according to the category of business under discussion: scientific matters are voted on by individual members, whereas administrative and financial decisions are determined by national representatives, with votes weighted according to subscription levels. Statute revisions require a supermajority and a minimum turnout, reinforcing the Union’s emphasis on broad consensus.
The General Assembly meets every three years, with the exception of the wartime interval between 1938 and 1948. In 1973, an Extraordinary General Assembly was held in Warsaw to commemorate the 500th anniversary of Nicolaus Copernicus’ birth.

Organisational Structure

The IAU is organised into divisions, commissions, and working groups, each responsible for a particular scientific or organisational theme. Notable groups include:

• Working Group for Planetary System Nomenclature (WGPSN): Oversees standard naming conventions for planetary bodies.
• Working Group on Star Names (WGSN): Standardises proper names for stars.
• Central Bureau for Astronomical Telegrams: Coordinates rapid communication of astronomical observations.
• Minor Planet Center: Manages identification and tracking of minor Solar System bodies.

The Union’s Secretariat is located within the Institut d’Astrophysique de Paris, in the 14th arrondissement.

Leadership

The IAU has been led by numerous distinguished astronomers since its inception. Early Presidents included Benjamin Baillaud (1919–1922), William Wallace Campbell (1922–1925), and Willem de Sitter (1925–1928). Later Presidents have included Jan Oort, Victor Ambartsumian, Otto Heckmann, Adriaan Blaauw, Vainu Bappu, Robert Hanbury Brown, Catherine Cesarsky, Norio Kaifu, and Silvia Torres, reflecting the Union’s global and disciplinary diversity.

Influence and Contemporary Role

The International Astronomical Union remains central to the global astronomical community. Its work in defining, standardising, and disseminating astronomical terminology and classification—most famously the definitions of planets and dwarf planets—has far-reaching effects in research, education, and public communication.
Through conferences, international cooperation, and outreach programmes, the Union fosters scientific development worldwide, supporting both advanced research and capacity-building in regions with emerging astronomical communities. As astronomy continues to expand into new observational domains and planetary exploration accelerates, the IAU’s authority and collaborative role remain indispensable to the coherence and progress of the field.