During the 100 years of the International Astronomical Union, the worldwide astronomical publications have grown exponentially, converted almost entirely to English, and changed format from observatory publications to journals to online publications. Observatory publications, conference proceedings, and individual theses have nearly disappeared in usefulness for research.

This paper presents my own recollections of the difficult relations that existed between the IAU and a fraction of the public, especially in the USA, following the IAU decision to reclassify Pluto as a dwarf planet at the 2006 General Assembly in Prague, and which ultimately led the IAU to organize the NameExoWorlds international contest to give public names to selected exoplanets and their host stars. In spite of the success of the International Year of Astronomy in 2009, the Pluto controversy continued, and its consequences climaxed during my term (2012-2015), as NASA’s New Horizons probe approached Pluto for a flyby just before the 2015 General Assembly in Honolulu. It was during this period that the IAU launched the NameExoWorlds contest, which also came to a conclusion in Honolulu after over half a million votes were cast from all over the world. While the inside story of how the contest was organized has appeared elsewhere, here I focus on the historical and sociological context that made Pluto such a sensitive issue, especially in the USA, explaining why this contest generated another controversy between the IAU and the New Horizons team. However, after the world-wide success of NameExoWorlds, the IAU and the New Horizons team eventually reached an agreement on finalizing the characterization and names of a number of newly discovered Pluto and Charon surface features (an on-going process), while a new edition of NameExoWorlds is in preparation for the IAU centennial in 2019.

During the last twenty years, due to the extensive help and assistance of the international scientific community, there has been a great success in the development and establishment of new well-functioning and competitive scientific groups specialized in general relativity and relativistic astrophysics in Uzbekistan (Tashkent), Kazakhstan (Astana and Almaty), Kyrgyzstan (Bishkek) and great achievements have been made on the study in Central Asia in relativistic cosmology and astrophysics of compact gravitational objects.

In 1539 the Italian Giovanni Paoli, better known as Juan Pablos, began operating in Mexico City the first printing press that existed in the New World. The first books he printed were religious texts, vocabularies of some indigenous languages of Mexico, and compilations of ordinances and laws. In 1556 followed the Sumario compendioso de las cuentas, a text of arithmetic and algebra that was the first American mathematics book. A year later, he printed the Physica Speculatio by friar Alonso de la Veracruz, a text of Natural Philosophy that dealt with Aristotelian works such as Physics, On the Heavens, and Meteorology. As part of this book, was included the text of geocentric astronomy written during the thirteenth century by the Italian mathematician Giovanni Campano de Novara, entitled Tractatus de Sphaera, where the author discussed, from a geometric perspective, the cosmic structure and the stellar distribution. No doubt this is the first astronomical treatise that was published in the entire American continent, which is why it is emphasized here.

The astronomical community accepts the division of the celestial sphere into 88 constellations, according to what was established by the IAU. In the first Assembly of 1922 the use of Latin names for constellations and their abbreviations was resolved. The pending issue of the limits of the constellations was discussed in the next meeting and Eugène Delporte had the responsibility for the complete theoretical demarcation. For his work, Delporte took into account what was done half a century earlier in the famous work Uranometría Argentina, published in 1877 and 1879, under the supervition of Benjamin Gould. In ths presentation we discusse the situation at the moment when the constellation boundaries were proposed using arcs of RA circles and parallels of declination, choosing them in such a way that they did not deviate too much from those used in the most important celestial atlas of the time, and minimizing the changes of which constellations stars would belong to.

The Czech astronomer František Nušl (1867–1951) was professor of mathematics, practical astronomy and geometrical optics at Prague Charles University. His scientific contribution to astronomy consisted mainly of inventing and constructing of new astronomical and geodetical instruments. Together with his friend Josef Jan Frič, founder of the Ondřejov Observatory, he developed and improved the circumzenithal telescope (1899–1903–1906–1922–1932), a portable instrument with a mercury horizon for determining the geodetic position using the Gauss method of equal altitudes. This instrument won the gold medal at the Exposition Internationale des Arts et Techniques dans la Vie Moderne in Paris in 1937. Nušl, independently of Ernst Öpik, invented the wobbling mirror for determining the velocity of meteors by visual observation, and constructed an unique guiding system for the Ondrejov astrograph etc. The organizational activities of Frantisek Nušl were considerably rich, too: He was one of the founders of the Czech Astronomical Society in 1917, in the years 1922–1948 he served as its president. From 1918 until his retirement in 1937 he was the director of the Ondrejov Observatory, 40 km south of capital city of Prague, lectured astronomy at the Prague university and held many popular lectures including regular courses in radio broadcasting. František Nušl was member of several commisions of international scientific unions; he organized the 3rd General Assembly of IUGG (International Union of Geodesy and Geophysics) in Prague 1927, and in IAU (International Astronomical Union) he was elected as Vice-President in the years 1928–1935. One can conclude that he was the main person who formed the Czech astronomy in the interwar period.

We briefly discuss the history of membership and the current position of Serbia inside the International Astronomical Union. We give an overview of astronomy education, research and public outreach in Serbia. Some statistics are presented concerning the number and gender of BSc, MSc and PhD students that graduated/obtained their degree in astronomy/astrophysics from the Department of Astronomy, Faculty of Mathematics, University of Belgrade. Due attention is paid to the most important scientific/educational institutions in Serbia in which the majority of astronomers are employed as well as various research topics investigated.

The first hundred years of the IAU have witnessed scientific and technological progress in astronomy beyond anything imagined at the time the IAU was founded in 1919. What will the next hundred years bring? How do we engage with other sciences, now that our field is becoming more multidisciplinary? How do we convince governments to continue funding our field, in particular the ever more powerful telescopes? And how do we continue to inspire and involve people worldwide in our exciting adventure through space? A brief forward look into the next decade and beyond is presented, with some challenges highlighted.

This paper presents a brief survey on the history of radar observations of meteors in Kazan from 1950s to present days. Such achievements of Kazan researchers as development and further improvement of original measuring equipment and antenna systems, of observational data processing methods, their contribution to the theory of physics of meteor phenomena and theoretical interpretation of experimental data are highlighted. A particular progress in meteor astronomy has been achieved with a new discrete quasi-tomoghraphic method for faint meteor showers identification that uses goniometer data of meteor radio reflections detected on radar as input data. The current state and new horizons of meteor studies in Kazan are stated.

The so-called China crisis, well documented in History of the IAU by Adriaan Blaauw and in Under the Same Starry Sky: History of the IAU by Chengqi Fu and Shuhua Ye, refers to the withdrawal in 1960 of the People’s Republic of China (PRC) from the Union. The crisis stemmed from the admission by the IAU, amidst strong protest from PRC and some other member countries, of the Republic of China (ROC) to the Union, creating the so-called “Two Chinas” – or “One China, one Taiwan” problem. The crisis directly led to the absence of mainland Chinese astronomers from the stage of international collaborations and exchanges, and was only solved two decades later. The solution, accepted by all the parties involved, is that China is to have two adhering organizations, with mainland China astronomers represented by the Chinese Astronomical Society located in Nanjing (China Nanjing) and China Taiwan astronomers represented by the Academia Sinica located in Taipei (China Taipei). The denominations “China Nanjing” and “China Taipei” represent the IAU official resolution and should be used in all IAU events.

The China crisis, probably the most serious one in IAU history, was a painful lesson in the 100-year development of the Union. Yet, with its eventual solution, the Union has emerged stronger, upholding its spirit of promoting astronomical development through international collaboration of astronomers from all regions and countries, regardless of the political systems, religion, ethnicity, gender or level of astronomical development.

Prof. Jorge Sahade (1915–2012) was the first Latin American President of the International Astronomical Union (1985–1988). From then on, he had a very active participation as president, vice-president, and organizing committee member of several Commissions and Divisions of the IAU, related to stellar astrophysics and exchange of astronomers. Prof. J. Sahade was born in Argentina and was one of the first students graduated in astronomy at the National University of La Plata. He served as director of the Astronomical Observatory of Córdoba (1953–1955) and of the Observatory of La Plata (1968–1969). He was the first Dean of the Faculty of Exact Sciences of the National University of La Plata. He promoted the purchase of a 2.15-m diameter telescope, today located in the Complejo Astronómico El Leoncito, San Juan, Argentina. He founded the Institute of Astronomy and Physics of Space (IAFE) in Buenos Aires and was its first director (1971–1974). He was also director of the “Comisión Nacional de Actividades Espaciales” (the Argentina Space Activity Agency) and promoted the inclusion of Argentina as a partnership of the Gemini Observatory. Prof. Sahade also focused on the development of the astronomy in Latin America and this led to the creation of the “Liga Latinoamericana de Astronomía” (nowadays LIADA).

His research field was interacting binary systems and he published about 150 papers, among them is the well-known discovery of the “Struve-Sahade effect”. I met him when he was 70 years old; he was a very enthusiastic astronomer, who travellled everywhere to promote the astronomy in Latin America (Argentina, Perú, Honduras). Among his last dreams was the creation of a Latin American Institute to develop and enhance astrophysics in South and Central America, the revival of UV astronomy and many more impressive works that he would have liked to end and publish.

This paper addresses the relationships between Arthur S. Eddington, former director of the Cambridge Observatory (1914-1944), with the International Astronomical Union. It is demonstrated that the Union was related to every major moment in Eddington’s scientific career. New historical elements are brought forward, in the last section of the paper, to demonstrate Eddington’s action in favour of German colleagues during the Second World War.

Benjamin Baillaud was appointed president of the First Executive Committee of the International Astronomical Union which met in Brussels during the Constitutive Assembly of the International Research Council (IRC) on July 28th, 1919. He served in this position until 1922, at the time of the First General Assembly of the IAU which took place in Rome, May 2–10. At that time, Baillaud was director of the Paris Observatory. He had previously been director of the Toulouse Observatory for a period of 30 years and Dean of the School of Sciences of the University of Toulouse. He specialized in celestial mechanics and he was a strong supporter of the “Carte du Ciel” project; he was elected chairman of the permanent international committee of the Carte du Ciel in 1909. He also was the founding president of the Bureau International de l’Heure (BIH) and he was directly involved in the coordination of the ephemerides at an international level. In this paper, we present some of his activities, particularly those concerning international programmes, for which he received international recognition and which eventually led to his election in 1919 to the position of first president of the IAU. We also briefly recount the very first meetings and years of the IAU.

The founding and development of two commissions of the IAU that played a unique role in IAU history are traced. Commission 38 for the Exchange of astronomers was founded in 1946 with Frederick Stratton as first president, and it expended funds (initially granted by UNESCO) for astronomers to travel on exchange visits. Commission 46 for the Teaching of astronomy was founded in 1964 with Evry Schatzmann as first president. This was a time of rapidly growing interest in the IAU for teaching astronomy and in due course for promoting astronomy in developing countries. For a while, both commissions operated under the wing of the Executive Committee. Their role was unique as they were the only IAU commissions to have their own budget, as well as aspiring to bring about social change in the astronomical community. By 2000 both commissions merged into C46 (Astronomy education and development) and by that time various programmes such as the International School for Young Astronomers (ISYA), the working group World-wide Development of Astronomy (WWDA) and the working group Teaching Astronomy for Development (TAD), which grew out of the Visiting Lecturers’ Program (VLP), were all run by C46. When the IAU established the Office of Astronomy for Development in 2011, many of these functions were removed from the commission and in any case C46 ceased to exist in 2015 when all the old commissions were disestablished. In 2015 the Office for Young Astronomers took over the running of the ISYA. The history of C38 and C46 represents a time of active change in the way the IAU was engaging with people. It was more than just a union for scientific research, but in the world of scientific unions, it was remarkable for taking an active hands-on role in implementing social change. In the history of these two commissions, the Swiss astronomer Edith Müller played a leading dynamic role. She served as president of C46 (1967-73), of C38 (1985-88) as well as IAU General Secretary (1976-79).

The history of the International Astronomical Union (IAU) meetings goes back to 1922 when the first IAU General Assembly (GA) was held in Rome, Italy, following the IAU creation in 1919. However, until 1953, no individual symposia were organized and the GAs were the only official gatherings for astronomers. All together, eight IAU GAs were held during 1922–1952. The IAU Symposium 1 was held in 1953 in Groningen, Netherlands. Starting with 1955, several IAU symposia were regularly held in different places, and since 1959, the IAU also began to organize colloquia to discuss relatively smaller topics. Twenty IAU colloquia numbered as I–XX were held in the period 1959–1971, and another series of IAU colloquia was organized in 1968–2005, numbered as Nos. 1–200. At present IAU symposia are the only official scientific meetings, nine of them being organized every year. IAU S349 “Under One Sky: the IAU Centenary Symposium”, held in Vienna during the IAU GA XXX, was the last one by number in 2018. Thus, the IAU has a 65-year history of symposia and all together 348 such meetings have been held, on average 5–6 annually. At present most of the IAU symposia during the years of GA are being organized in the framework of the GA, there being typically six symposia during each GA. All together, 31 IAU GA have been organized during the years 1922–2018, including 30 regular ones and one Extraordinary GA (1973 in Warsaw, Poland), typically once every three years. Since 1974, the IAU has also organized regional meetings in Europe, Asia and Pacific (APRIM), Latin America (LARIM), and the Middle East and Africa (MEARIM). The European ones were discontinued in 1990 after the creation of the European Astronomical Society (EAS) and the organization of the yearly JENAM/EWASS. The 348 IAU symposia have been organized in 43 countries. We give the statistics of all IAU symposia by year of organization, by various topics of astronomy and astrophysics, and by host countries and cities.

The research about women in astronomy began in 1988 following a request received from Wilfried Schröder, now deceased but, at that time, in charge of the Interdivision Commisssion on History, which was included in the International Association of Geomagnetism and Aeronomy (IAGA) attached to the IUGG International Union of Geodesy and Geophysics. The results obtained concerning “Astronomy, Geophysics and Women”, presented at the symposium “The history of geomagnetism and aeronomy”, were published (Débarbat 1989) in Advances in Geosciences in the form of a short paper. The IAU began to publish, in 1992, membership statistics in its Information Bulletin IB 68, including percentages of women and men, and several papers were published on the subject up to the last one Statistics on Women in IAU Membership (Débarbat 1989). Recent results are given including examples from the past.

Astronomy, astrophysics and cosmology have changed out of all recognition over the last 100 years. The IAU has provided an essential means of fostering international collaboration in these disciplines including times of international tension. Developments will be highlighted which have profoundly changed our understanding and insight into the workings of our Universe.

Of all the sciences, astronomy is by far the most border-less in its activities, and the most advanced in its concepts of collaborating across borders. In their dealings and in their needs, today’s teams are mature enough to ignore gender differences and ethnic differences, and across the past 50+ years of IAU membership which I personally can chalk up, the IAU personnel, Commissions, and other bodies have come to reflect more nearly the same – albeit small – gender ratios as found in its member institutions. In the IAU there has always been space for the individual, and if one recalls the early contributions to the IAU by major players like Edith M¨uller, Giusa Cayrel, Anne Underhill and Charlotte Moore, I think it can be said that astronomy was, and knew it was, better off by giving such people the latitude that they deserved as scientists, rather than because they were women. When a meeting in Baltimore in 1992 was called to discuss “Women in Astronomy”, the pressure came from the younger generations, who feared that the low percentages of tenured women in astronomy would be allowed to continue unnoticed, so they created the Baltimore Charter to draw attention to what certainly appeared to some as discrimination. Even though there could be no quick fixes to the situation, and the winds of change have been more like zephyrs than the cleansing gales that some hoped for, the percentage of women now rising through the ranks is definitely on the increase, and is witnessing growing ethnic diversity. Those are a matter of pride for the IAU, and must be highlighted in this its Centenary Year.

The South African Astronomical Observatory (SAAO), formerly known as the Royal Observatory, Cape of Good Hope, will be 200 years old in 2020. Also, South Africa (SA), formerly a British colony known as the Cape of Good Hope, will celebrate her 100-year anniversary as an International Astronomical Union (IAU) member in 2020, following the IAU centenary in 2019 that this IAU Symposium 349 celebrates. In light of all this, particularly in anticipation of the 200-year anniversary of SAAO in 2020, the SA National Research Foundation (NRF) has developed a Roadmap for the History of Astronomy in South Africa. As part of this we are conducting an oral history of astronomers to complement the historical celebrations of the institutions and science relating to astronomy in SA, supported by the SA NRF. Primarily drawing on literature and setting the scene for this work, here we present a snippet of the on-going oral histories, to glean the role of the IAU in astronomy in South Africa and show the potential of the oral histories to inform and complement written history.

OAD, the Office of Astronomy for Development, one of the most significant innovations within the IAU, was created at the XXVII General Assembly in Rio de Janeiro in 2009 and opened in 2011. The new office brought together and strengthened several activities of the IAU aimed at helping astronomers in developing or isolated countries to keep in touch with their colleagues elsewhere and up-to-date with the developments in our science. Those activities were mediated through the old commission structure by Commission 38 (Exchange of Astronomers) and Commission 46 (Astronomy Education and Development) which oversaw the International Schools of Young Astronomers (ISYA), the Visiting Lecturer Programme (VLP) and Teaching for Astronomy Development (TAD). In addition, Jorge Sahade, during his term as IAU President (1985–1988), formed the Working Group for the Promotion and Development of Astronomy, as a sub-committee of the Executive Committee, and asked the present writer, then a Vice-President, to act as chair. That Working Group (later renamed the Working Group for the Worldwide Development of Astronomy, WGWWDA) operated within the context of the already existing services of the IAU and in cooperation with the United Nations Committee on the Peaceful Uses of Outer Space (COPUOS). In this paper, the writer gives an account of the activities of the WGWWDA both during and between General Assemblies, until the year 2000, shortly after which he relinquished responsibility for them.