History of the International Astronomical Union

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The International Astronomical Union was founded in Brussels, in 1919 and drew together the work of a number of pre-existing international projects. However, the idea of a coordinating international astronomical association first occurred to American astronomer George Hale in 1904. As someone who had travelled throughout Europe after studying in the MIT and Berlin, Hale had a number of international contacts, and he understood the value of collaboration between astronomers of different nationalities, having observed projects such as the Carte du Ciel (Map of the Sky, discussed below) and the Astronomische Gesellschaft Katalog (an important star catalogue). After obtaining positive feedback from his friends in Europe, he proposed the creation of an organization that would make such cooperation easier to the National Academy of Sciences of the United States. They accepted his proposal and put Hale in charge of a committee with the objective of bringing it to fruition.

Hale decided, at least initially, to focus his efforts in solar research, his own area of study. He sent invitations to academies and scientific societies in Europe. Of the 17 invited academies, only the Prussian Academy of Sciences declined, and the rest assisted the meeting organized by Hale at the International Congress of Science at St Louis in 1904 (which coincided with the St Louis Exposition). In the meeting, they appointed a committee composed of a representative from each participating country. The committee created a constitution for the now named International Union for Cooperation in Solar Research. In their second conference (Oxford, September 1905), they focused on scientific problems over bureaucratic minutia and produced many important results: Alfred Fowler presented results about the spectrum of sunspots and Hale and Deslandres suggested several applications for the spectroheliograph (which later helped Hale discover the magnetic fields in sunspots), among other things. They were published in the Transactions of the Union, which became a recurring publication after each meeting (a tradition the IAU also followed).

The Union was accepted by the International Association of Academies in 1907 (it had not been before due to Prussian opposition) and a third conference was held in Paris, also in 1907. In the fourth conference, held in Mount Wilson, California, in 1910, stellar research and astrophysics were also included in the programme, in an effort to expand the Union’s research to other areas of astronomy that might benefit from international collaboration. The conferences were meant to take place every three years, but, after the one held at Bonn in 1913, the First World War (1914-18) broke out, and international collaboration was stopped to a halt. The long war, and the bitterness that followed it, lead to the disappearance of the Union, as well as the International Association of Academies, which also held its last meeting in 1913.

The desire for collaboration to bring science forward, however, resurfaced once the War ended. The National Research Council of the United States, where George Hale now worked, joined forces with the Royal Society of London and the Paris Academy of Sciences to create the International Research Council in Brussels, in 1919. The Council, formed then by 12 countries, had the objective of promoting international cooperation in the sciences. To this end, it created a number of internal unions that dealt with different areas of study. The International Astronomical Union was one of these, officially created on 28 July 1919.

The IAU took upon the duties previously held by the International Union for Cooperation on Solar Research, but also by other international astronomical groups. One of these was the Carte du Ciel (Map of the Sky), one of the oldest international astronomical projects. It had been launched in Paris, in 1887, and it had the objective of carrying out a photographic map of the entire celestial sphere. Eighteen observatories collaborated on this colossal task, which would require of at least 20600 photographic frames. The IAU continued the project (put in charge of Commission 23) until 1970, when it was left unfinished. The first President of the IAU, Edouard Benjamin Baillaud, then Director of the Paris Observatory, had been one of the people in charge of the Carte du Ciel before the Great War. Baillaud was also the founder of the Bureau International de l’Heure (International Time Bureau), which researched time keeping. It was assimilated by the IAU, becoming Commission 31.

The IAU soon became the leading astronomical organization. The 7 countries that had joined in 1920 increased to 31 by 1949, and even scientists from countries that had not joined yet (like Germany or Austria) regularly attended the meetings. The IAU held their General Assemblies approximately every 3 years, with the first one taking place in Rome, in 1922. After the 1938 meeting in Stockholm, the General Assemblies stopped due to the Second World War, but they soon restarted with the August 1948 meeting in Zurich.

In the Assembly, the members chose an Executive Committee, formed by a President, several Vice-Presidents and a General Secretary (which also acted as a treasurer). Their duty was to manage the IAU’s finances and prepare the next General Assembly. The IAU established different commissions (there were 41 by 1949) which covered different branches of astronomy. In 1958, under General Secretary Donald Sadler, the IAU started publishing the biannual Information Bulletin, which served to keep all members up to date with the goings-on of the Union. The IAU Circulars were a series of postcards with information on recent discoveries that required prompt dissemination.

In 1973, the General Assembly was to be celebrated in Sidney, Australia. This was the first time an important meeting of this kind was to be held in the southern hemisphere. However, this decision put the IAU in danger of splitting up: 1973 was the year of the quincentenary of Nicolaus Copernicus’ birth, so Polish astronomer Wilhelmina Iwanowska proposed that the General Assembly be held in Poland, in celebration of such an occasion. Many astronomers from Eastern Europe supported this proposal, discouraged by the idea of going on a long and expensive trip to Australia. Others, however, pointed out that changing the site of the Assembly at such a late date would be an offense to all of the members of the IAU that lived in the southern hemisphere, Australians in particular, since they had taken that same trip in all previous meetings. The Executive Committee, led by President Otto Heckmann, reached a middle ground. They celebrated the 1973 General Assembly in Sidney, as planned, but they also held an Extraordinary General Assembly in Warsaw one month later (circumventing the clause in the IAU Constitution that impeded them from holding two General Assemblies in the same year).

The Chinese (through the National Committee of Astronomy at Nanjing) joined the IAU in 1935, but they left in 1961, just prior to the General Assembly in Berkeley, California. This was a reaction to the acceptance of Taiwan (through the Astronomical Society of Taipei) to the IAU. Taiwan, or officially the Republic of China, claimed to be the legitimate government of all of China. It enjoyed the political protection of the United States, but it was not recognised by the People’s Republic of China. Many astronomers considered the exit of China a big loss, since astronomy had been present in China for longer than in Europe, but the Executive Committee was not willing to go back on its acceptance of the Taiwanese (a measure other international scientific unions had taken when faced with a similar dilemma). The Cultural Revolution that took place in China in the following years only made it harder for the Chinese to return to the IAU. Negotiations only started in 1979, years after the United Nations had stopped recognising the sovereignty of Taiwan. The President of the IAU, Adriaan Blaauw, held several meetings with a Chinese delegation, led by astronomer Chang Yu-Che, before and after the Montreal General Assembly, in which the Taiwanese were also involved. The negotiations were successful and the Chinese re-joined the IAU. In 2012, the XVIII General Assembly was held in Beijing.

In 1988, under the proposal of President Jorge Sahade, the IAU created the position of President-Elect, which future presidents would occupy for 3 years before taking charge of the presidency. This way, they would familiarise themselves with the inner workings of the IAU, resulting in them being more prepared for their job. Under the presidency of Lodewijk Woltjer, in an effort to stop younger members from disconnecting from the General Assemblies, the Hague General Assembly of 1994 included more scientific content, incorporating 6 symposia and colloquia (instead of holding them independently). The IAU also inaugurated its official webpage in December 1994 and, in the last decade of the 20th Century, started publishing their Informational Bulletins in digital form, starting with No. 74 (January 1995). In 2006, the IAU started issuing the electronic IAU Newsletters, containing short announcements of urgent nature.

The IAU has always been concerned with the dissemination of astronomy and with the public understanding of the importance of the science. In 2009, under President Catherine Cesarsky, it celebrated the International Year of Astronomy, coinciding with the 90th anniversary of the institution and the 400th of Galileo's first telescope observations and the publication of Kepler’s Astronomia Nova.


I 1922 Rome, Italy Benjamin Baillaud Alfed Fowler
II 1925 Cambridge, UK William W. Campbell Alfred Fowler
III 1928 Leiden, Netherlands Willem de Sitter Frederick J. M. Stratton
IV 1932 Cambridge, MA, USA Sir Franck Dyson Frederick J. M. Stratton
V 1935 Paris, France Franck Schlesinger Frederick J. M. Stratton
VI 1938 Stockholm, Sweden Ernest Exclangon Jan H. Oort
VII 1948** Zürich, Switzerland Sir Harold Spencer Jones Jan H. Oort
VIII 1952 Rome, Italy Bertil Lindbald Bengt Strömgren
IX 1955 Dublin, Ireland Otto Struve Pieter Th. Oosterhoff
X 1958 Moscow, USSR André Danjon Pieter Th. Oosterhoff
XI 1961 Berkeley, CA, USA Jan H. Oort Donald H. Sadler
XII 1964 Hamburg, Germany Viktor A. Ambartsumian Donald H. Sadler
XIII 1967 Prague, Czechoslovakia Pol Swings Jean-Claude Pecker
XIV 1970 Brighton, UK Otto Heckmann Luboš Perek
XV 1973 Sydney, Australia Bengt Strömgren Cornelis de Jager
Extra 1973 Warsaw, Poland Bengt Strömgren Cornelis de Jager
XVI 1976 Grenoble, France Leo Goldberg George Contopoulos
XVII 1979 Montreal, Canada Adriaan Blaauw Edith A. Müller
XVIII 1982 Paras, Greece Manali K. Vainu Bappu Patrick A. Wayman
XIX 1985 New Delhi, India Robert Hanbury Brown Richard M. West
XX 1988 Baltimore, USA Jorge Sahade Jean-Pierre Swings
XXI 1991 Buenos Aires, Argentina Yoshihide Kozai Derek McNally
XXII 1994 The Hague, Netherlands Alexander A. Boyarchuk Jacqueline A. Bergeron
XXIII 1997 Kyoto, Japan Lodewijk Woltjer Immo Appenzeller
XXIV 2000 Manchester, UK Robert Paul Kraft Johannes Anderson
XXV 2003 Sidney, Australia Franco Pacini Hans Rickman
XXVI 2006 Prague, Czech Republic Ronald D. Ekers Oddbjørn Engvold
XXVII 2009 Rio de Janeiro, Brazil Catherine Jeanne Cesarsky Karel A. van der Hucht
XXVIII 2012 Beijing, China Robert Williams Ian F. Corbett
XXIX 2015 Honolulu, Hawaii, USA Norio Kaifu Thierry Montmerle
XXX 2018 Vienna, Austria Silvia Torres-Peimbert Piero Benvenuti
XXXI 2021 Busan, Republic of Korea Ewine F. van Dishoeck Maria Teresa V. T. Lago

*The presidents and secretaries above are ending their term at the indicated GA.
**During 1938-44, Arthur Eddington served as President and Walter S. Adams and Jan H. Oort as General Secretaries. No GA was celebrated due to WWII.


There are 73 national members as of July 2018, 6 of which are suspended:

Belgium 1920
Canada 1920
France 1920
Greece 1920
Japan 1920
United Kingdom 1920
United States 1920
Italy 1920 (1921)
Mexico 1921
Denmark 1922
Netherlands 1922
Norway 1922
Poland 1922
Romania 1922
Spain 1922
South Africa 1922 (1938)
Brazil 1922 (1961)
Czech Republic 1922 (1993)
Slovakia 1922 (1993)
Switzerland 1923
Portugal 1924
Egypt 1925
Sweden 1925
Argentina 1927
Vatican City 1932
China (Nanjing) 1935
Armenia 1935 (1994)
Estonia 1935 (1992)
Russian Federation 1935 (1992)
Lithuania 1935 (1993)
Tajikistan 1935 (1993)
Ukraine 1935 (1993)
Croatia 1935 (1994)
Georgia 1935 (1994) Suspended
Serbia 1935 (2003)
Australia 1939
Chile 1947
Hungary 1947
Ireland 1947
Finland 1948
Germany 1951
Venezuela 1953
Israel 1954
Austria 1955
Bulgaria 1957
China (Taipei) 1959
Turkey 1961
India 1964
New Zealand 1964
Indonesia 1964 (1979)
Iran 1969 Suspended
Uruguay 1970
Republic of Korea 1973
Iceland 1988
Malaysia 1988
Peru 1988 Suspended
Saudi Arabia 1988 Suspended
Morocco 1988 (2001) Suspended
Latvia 1996
Bolivia 1998 Suspended
Philippines 2001
Nigeria 2003
Lebanon 2006
Mongolia 2006
Thailand 2006
Costa Rica 2009
Honduras 2009
Panama 2009
Viet Nam 2009
Ethiopia 2012
Kazakhstan 2012
Democratic People's Republic of Korea 2012
Colombia 2015

The following national members were terminated:

Algeria 1988
Azerbaijan 1997
Macedonia 1998
Uzbekistan 1999
Cuba 2001
Jordan 2001

* Year in which they joined.

Article by: J. G. Mena

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