Fifty Highlights from Fifty Years


The year 2012 marks the 50th anniversary of the European Southern Observatory (ESO), the foremost intergovernmental astronomy organisation in the world. This very special year provides a great opportunity to look back at ESO’s history through its most important milestones, as it celebrates 50 years of reaching new heights in astronomy. Fifty selected highlights from the first 50 years of ESO’s history are marked below with superscripts. For a comprehensive timeline of ESO’s milestones see this.

A presentation with 50 selected highlights is available here.

The idea of a shared European observatory was discussed for the first time in late spring 19531 by a group of astronomers in Leiden, the Netherlands. They included Walter Baade and Jan Oort, Adrian Blaauw and Otto Heckmann. Oort would later become President of the ESO Committee and Heckmann and Blaauw ESO’s first and second Directors General respectively. From the start, they intended to build an observatory in the southern hemisphere. On 5 October 1962, representatives from five European countries — Belgium, France, Germany, the Netherlands and Sweden — signed the ESO Convention in Paris2. Their signatures represented a formal commitment to establish the European Organisation for Astronomical Research in the Southern Hemisphere, today commonly referred to as the European Southern Observatory.

In late 1963, Heckmann, then acting as ESO’s Director General, concluded an agreement with the Chilean government to establish ESO’s observatory in Chile3. ESO had originally planned to establish itself in South Africa, but site testing indicated that atmospheric conditions were better in the high and dry mountainous regions of the Chilean Atacama Desert. ESO was now set to build the observatory it had planned.

In spring 1964, after site testing, the exact site of the observatory was chosen4, a 2400-metre-high mountain, 600 kilometres north of Santiago de Chile. The site was nicknamed La Silla — the chair — due to its particular shape. The same year, ESO bought the land around the mountain5 from the Chilean government and was given a site in the capital Santiago to build its Chilean headquarters, next to the UN offices in the Vitacura district. In late November 1966, the observatory’s first telescope, 1 metre in diameter, started operations at La Silla6. Others would follow over the next few years, until the official inauguration of the observatory7 by the President of the Republic of Chile, Eduardo Frei Montalva, on 25 March 1969. ESO now officially had its observatory in the southern hemisphere. Yet, even before this, ESO grew, with Denmark joining as the sixth Member State in 19678.

Moving forward to the 1970s, the Organisation passed a number of major milestones. In November 1976, the 3.6-metre telescope, the jewel in the La Silla crown, envisioned since the inception of ESO, started operations9. This had been made possible thanks to a close cooperation with CERN in Switzerland, where ESO’s technical staff had moved in 1970. In 1978, the Quick Blue Survey was completed10 using the 1-metre Schmidt telescope, at La Silla, one of the original telescopes planned for in 1953. This survey was the first of its kind in the southern hemisphere, mapping the sky in detail and providing a basis for future observations. ESO had now completed its original mission to build and equip its observatory in the southern hemisphere with world-class telescopes.

In 1975, the Council, ESO’s sovereign body, decided to build the new headquarters in Garching bei München11, Germany, following an offer by the German government to host ESO. The move was meant to gather all of ESO’s European staff, which was spread out between Geneva and Hamburg, where ESO’s administration had been located since the creation of the Organisation. Construction began even before the German government and ESO formally agreed on the project in 1979, and the new offices, of a very original design, were inaugurated in 198112 in the presence of senior representatives from ESO and its Member States. The move in many ways transformed ESO into a full-fledged intergovernmental organisation, going beyond the role of providing a shared observatory to its Member States.

In 1982, two new states joined the Organisation: Switzerland13 and Italy14. Two new major telescopes were also added to the La Silla Observatory. In 1983, the MPG/ESO 2.2-metre telescope started operations15, and continues today to deliver stunning images thanks to the quality of its instruments. In 1989, the New Technology Telescope (NTT) arrived16, the first telescope in the world to be equipped with a computer-controlled mirror. This technology, known as active optics, was developed at ESO and is now applied to most of the world's large telescopes. Today, the NTT continues to provide high-quality observations.

The NTT was key to testing the viability of ESO’s new flagship project: the Very Large Telescope array (VLT), designed to be the world’s biggest optical telescope. The ESO Council approved the project in 198717 and Cerro Paranal was selected as its home in 199018, after the Chilean government had donated the land around it to ESO in 198819. Cerro Paranal is an isolated 2600-metre-high mountain in the Atacama Desert, one of the driest in the world.

As the 1980s concluded, ESO had a fully equipped and functional observatory at La Silla, and was already planning its next observatory, set to become a reference in the world of ground-based astronomy. It took ESO ten years to build the highly complex VLT, whose first telescope, named Antu — the Sun in the Mapuche language — saw First Light in May 199820. The official inauguration of the new observatory followed shortly afterwards and on 5 March 1999, the VLT was officially opened21 in the presence of the President of the Republic of Chile, Don Eduardo Frei Ruiz-Tagle. The VLT was now ready to make its contribution.

At the turn of the century, ESO had reached the forefront of astronomy and was ready to enter the 21st century. Confirming this status, events picked up pace. No less than seven new members would decide to join ESO during the next decade: Portugal in 200122, the UK in 200223, Finland in 200424, Spain25 and the Czech Republic26 in 2007 and Austria in 200927. Brazil signed the accession agreement at the end of 201028 and upon parliamentary ratification will become the first non-European member State and bring the total number of Member States to 15.


At Paranal, once all four major telescopes had been installed, the VLT Interferometer (VLTI) started operations in 200129, combining light from the telescopes for the first time. The VLTI is the only regularly operated large optical and infrared interferometric telescope in the world. In 2006, a bright yellow laser shot into the night sky from the VLT’s fourth telescope, Yepun, inaugurating the Organisation’s first laser guide star30. In 2009, a new telescope named VISTA joined Paranal31. VISTA is the world’s largest survey telescope, designed to map the night sky with high precision in near-infrared light. Finally in 2011, the VLT Survey Telescope, the VST, opened at Paranal32, as the world’s largest telescope surveying the sky in visible light. This arsenal of front-line telescopes combined with a plan to upgrade technologies including instruments built by institutes in the Member States, created the most advanced ground-based optical observatory in the world.

La Silla meanwhile saw a number of new instruments being added to its telescopes, among which is HARPS, the leading exoplanet hunter, which started operating in 200333.

In 2005, together with the Max Planck Institute for Radio Astronomy and Onsala Space Observatory, ESO built a new telescope, APEX, the Atacama Pathfinder Experiment34, partly based on experience gained from the Swedish-ESO Submillimetre Telescope (SEST) at La Silla in the 80s and 90s. These were ESO’s first steps in millimetre radio astronomy. APEX is designed to study the skies in submillimetre wavelengths. Located on the Chajnantor Plateau at 5000-metre altitude in the Atacama Desert of Chile, APEX was designed as a precursor to a much larger project, ALMA, the Atacama Large Millimeter/submillimeter Array.


In 2001, ESO signed an agreement with North America to build ALMA35 on the Chajnantor Plateau (Japan joined in 2004). This gigantic project came as a merger of three individual observatory projects following site testing from 1995 and onwards. ALMA is the world’s largest observatory project and will be a single telescope composed of 66 high-precision antennas that will study the Universe at millimetre and submillimetre wavelengths. In 2003, the Republic of Chile granted free concession of the land on Chajnantor for the execution of the ALMA project36. In 2006, it was decided that ESO would build ALMA’s headquarters next to ESO’s own Santiago offices in the Vitacura district. ALMA's construction will be completed in 2013, but early scientific observations with a partial array began on 30 September 201137, providing the world with a taster of ALMA’s full capability.

In parallel with, and building on, this collaboration project, in 2006, ESO set plans in motion to build its new flagship observatory, the Extremely Large Telescope38 or ELT. With its 40-metre-class optical/near-infrared telescope, the ELT will become “the world’s biggest eye on the sky. In April 2010, Mount Armazones, located 20 kilometres from Paranal, was chosen as the site for the Observatory39 and in October 2011, the Chilean government donated the land surrounding the mountain to ESO40. With the start of operations planned for early in the next decade, the ELT will tackle some of the biggest scientific challenges of our time, and surely revolutionise astronomy in ways we cannot even imagine yet.

These milestones in ESO’s history have led to a number of major scientific breakthroughs which were made possible thanks to the dedication of ESO’s teams, the quality of its instruments and the ingenuity of the astronomical community. Of these, ten stand out for their significance. They are bound to change over time as ALMA and the ELT become operational, but they are a testimony to the quality of ESO’s various observatories as it celebrates its 50th anniversary.

In December 1998, two independent research teams studying exploding stars partly with the 3.6-metre and the NTT telescope at La Silla showed that the expansion of the Universe is accelerating41. They were awarded the 2011 Nobel Prize in Physics for this result.

The year 2004 was rich in discoveries. In April, after more than 1000 nights of observations at La Silla spread over 15 years, astronomers determined the motions of more than 14 000 Sun-like stars42 in the neighbourhood of the Sun, showing that our home galaxy has led a much more turbulent and chaotic life than previously assumed. In August of the same year astronomers measured the age of the oldest star known in the Milky Way43: 13.2 billion years old, and in September, the VLT obtained the first-ever image of a planet outside the Solar System44.

In 2005, ESO telescopes provided definitive proof that long gamma-ray bursts are linked with the ultimate explosions of massive stars45, solving a long-standing puzzle which had started with NTT observations of a similar object in 1998.

The year 2008 was also filled with new results, with the VLT detecting carbon monoxide molecules in a galaxy seen as it was almost 11 billion years ago46 for the first time, allowing astronomers to obtain the most precise measurement of the cosmic temperature at such a remote epoch. In November, the VLT and APEX teamed up to study violent flares from the supermassive black hole at the centre of the Milky Way47 revealing material being stretched out as it orbits in the intense gravity close to the central black hole and in December, several of ESO’s flagship telescopes concluded a 16-year-long study to obtain the most detailed view ever of the surroundings of the supermassive black hole lurking at the heart of our galaxy48.

In January 2010 the first direct spectrum of an exoplanet49 and its atmosphere was obtained using the VLT, and in August 2010, astronomers using HARPS discovered the richest planetary system so far50, containing at least five planets around the Sun-like star HD 10180.

ESO’s history is filled with many milestones, evidence of the passion and vision of its founding fathers, staff, and the community throughout the years. Over 50 years, ESO has grown beyond its original mission to become the world’s most productive observatory. It carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries and plays a leading role in promoting and organising cooperation in astronomical research. This vision is ESO’s trademark and it is sure to remain the driving force at the heart of ESO’s activities as ESO aims to reach new heights in astronomy in 2012 and beyond.