The European Southern Observatory (ESO) is 60 years old. An opportunity to look back at the links that ULiège has with the largest European observatory.

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Since 1962, the University of Liège has maintained close relations with the European Southern Observatory (ESO). From the first Belgian representatives at ESO, who were pioneers from Liège and very much in favor of this astronomical adventure in the southern hemisphere, to the discovery of the TRAPPIST-1 system of exoplanets by a ULiège telescope installed on an ESO site, and including technological and instrumental developments for the VLT and the future ELT, the University of Liège has a long history with ESO. In December, Belgian scientists were able to blow out the candles of ESO's 60e anniversary at a meeting organized at the Brussels planetarium with a strong presence of researchers from ULiège.


he European Southern Observatory, officially named the European Organization for Astronomical Research in the Southern Hemisphere, is an intergovernmental organization for astronomy founded in 1962 by five European countries, including Belgium, to create a state-of-the-art ground-based astronomical observatory to enable European astronomers to observe the skies of the Southern Hemisphere.

ESO's mission is to design, build and operate powerful state-of-the-art ground-based observatories and to foster international collaboration in astronomy. Such infrastructures require international collaboration not only to bring together the relevant expertise at the cutting edge of technology, but also colossal financial resources. Thus, ESO aims to provide the scientists of its member states with research tools that a single state could not afford. ESO's decisions are taken by the ESO Council, which has one scientific and one political representative from each Member State.

ESO is the main player in European observational astronomy. It has numerous telescopes ranging from 2.2 to 8.20 m in diameter and a fleet of some twenty state-of-the-art instruments, enabling observations in imaging, photometry, spectroscopy and interferometry in almost all wavelengths from the near ultraviolet to the thermal infrared. The organization also has a comprehensive data archiving system, in partnership with the European Coordination Agency and the Hubble Space Telescope.

ESO employs about 730 people and receives an annual contribution from the Member States totalling about 200 million euros. 

While the telescopes are located in the Atacama Desert in Chile, the observatory is headquartered in Garching near Munich, Germany, with offices in Santiago, the capital of Chile. In 2022, ESO has 16 European Member States and three observing sites, all in Chile: the historic La Silla Observatory, the Cerro Paranal Observatory (where the Very Large Telescope (VLT) is located) and the Llano de Chajnantor Observatory, where the 64 radio antennae of the Atacama Large Millimeter/submillimeter Array (ALMA) are located. ESO has also embarked on a pharaonic project, the Extremely Large Telescope (ELT), a giant telescope with a diameter of 39 m, which is being built on Cerro Armazones, a mountain near Paranal, and which in 2028 will be the largest telescope in the world, opening up unique possibilities for European astronomers.

Belgium is one of the five founding members of ESO. It participated in the signing of the ESO Convention on 5 October 1962 and officially became a Member State in 1967. As a founding member, Belgium has been involved in many ESO projects over the years. Belgian astronomers, engineers and industry have benefited in many ways.  Belgium currently contributes 2.98% of ESO's income , worth EUR 6 780 000.

ESO at a glance

Image composition showing all the ESO observatories and the Headquarters. (Credit:ESO/M. Kornmesser)

ESO Belgian Day

This year marks the 60th anniversary of the institution, which now has 16 member countries. Belgian scientists wanted to mark the occasion and gathered at the Brussels planetarium last December for the ESO Belgian Day. 150 people, including some 60 master's and doctoral students from all the country's universities, took part in this day," explains Emmanuel Jehin, astronomer and FNRS Senior Research Fellow at the University of Liège, co-organizer of the event and new Belgian scientific representative on the ESO Council. Workshops and numerous scientific and technical presentations highlighting the use by Belgian scientists of the various ESO facilities as well as the implications for the development of new instruments were held throughout the day. We were very pleased with the quality of the presentations and the interaction between the different participants! Belgian ESO astronomers presented live the observatories from Chile in the planetarium dome, Belgian ESO students and former ESO staff members gave their testimonies, such as the very interesting and funny one about the first astronomers at La Silla. This event is an opportunity to highlight the links between ULiège and ESO as well as the scientific advances made by our researchers, thanks to ESO's infrastructure and instrumentation.

A long history between ESO and ULiège

The first Belgians to be elected to key positions at ESO were from Liège! Among them are the astrophysicist Pol Swings - who discovered the first interstellar molecule and was President of the International Astronomical Union - and Paul Ledoux, whose important work focused on the internal structure of stars. Both were chairmen and vice-chairmen of the ESO observing programme selection committee for several years, Paul Ledoux was also chairman of the ESO Council from 1982 to 1984 and Jean-Pierre Swings, Pol's son and a retired astrophysicist from the ULiège, was vice-chairman from 1995 to 1997. The latter played an important role in the selection of Paranal as the site for the Very Large Telescope (VLT), one of the best astronomical sites on the planet. Since 2020, Emmanuel Jehin, astrophysicist at the STAR Institute of ULiège, is the Belgian scientific representative on the ESO Council.

Many astrophysicists from Liège have worked at one of the ESO sites, observatories or research centers in Chile or Europe, since its creation, either as doctoral students or post-doctoral students, as astronomers in charge of observations or as engineers working on telescope or instrument projects. Some of them now hold positions of responsibility within ESO, such as Alain Smette and Gautier Mathys in Chile and Olivier Hainaut at ESO headquarters in Munich.

The know-how of Liège is also to be found at ESO in the contribution to very important technical projects such as the construction by AMOS of the four Auxiliary Telescopes (AT) of the VLT interferometer which made its first light in 2004. AMOS is also in charge of the construction of some of the mechanical and optical elements of the ELT.


Astronomers Michaël Gillon and Emmanuel Jehin installed the 0.60-m TRAPPIST-Sud robotic telescope at La Silla in 2010 with the help of the FNRS, and in 2019 the four 1-m telescopes of the SPECULOOS project, funded by an ERC, made their first light from Paranal. These telescopes are in operation almost every night in Chile to study exoplanets and small solar system bodies.

More recently, Olivier Absil, one of the co-investigators of the METIS infrared spectrograph, one of the future instruments of the ELT, is developing with his team the high contrast imaging modes, which will allow direct photography of planetary systems close to our own.

Read also : ESO : 50 years of space observations

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