The European Organisation for Astronomical Research in the Southern Hemisphere, commonly referred to as the European Southern Observatory (ESO), is an intergovernmental research organisation made up of 16 member states for ground-based astronomy. Created in 1962, ESO has provided astronomers with state-of-the-art research facilities and access to the southern sky. The organisation employs over 750 staff members and receives annual member state contributions of approximately €162 million. Its observatories are located in northern Chile.
ESO has built and operated some of the largest and most technologically advanced telescopes. These include the 3.6 m New Technology Telescope, an early pioneer in the use of active optics, and the Very Large Telescope (VLT), which consists of four individual 8.2 m telescopes and four smaller auxiliary telescopes which can all work together or separately. The Atacama Large Millimeter Array observes the universe in the millimetre and submillimetre wavelength ranges, and is the world's largest ground-based astronomy project to date. It was completed in March 2013 in an international collaboration by Europe (represented by ESO), North America, East Asia and Chile.
Currently under construction is the Extremely Large Telescope. It will use a 39.3-metre-diameter segmented mirror, and become the world's largest optical reflecting telescope when operational towards the end of this decade. Its light-gathering power will allow detailed studies of planets around other stars, the first objects in the universe, supermassive black holes, and the nature and distribution of the dark matter and dark energy which dominate the universe.
ESO's observing facilities have made astronomical discoveries and produced several astronomical catalogues. Its findings include the discovery of the most distant gamma-ray burst and evidence for a black hole at the centre of the Milky Way. In 2004, the VLT allowed astronomers to obtain the first picture of an extrasolar planet (2M1207b) orbiting a brown dwarf 173 light-years away. The High Accuracy Radial Velocity Planet Searcher (HARPS) instrument installed on the older ESO 3.6 m telescope led to the discovery of extrasolar planets, including Gliese 581c—one of the smallest planets seen outside the Solar System.
Past
The idea that European astronomers should establish a common large observatory was broached by Walter Baade and Jan Oort at the Leiden Observatory in the Netherlands in spring 1953. It was pursued by Oort, who gathered a group of astronomers in Leiden to consider it on 21 June that year. Immediately thereafter, the subject was further discussed at the Groningen conference in the Netherlands. On 26 January 1954, an ESO declaration was signed by astronomers from six European countries expressing the wish that a joint European observatory be established in the southern hemisphere.
At the time, all reflector telescopes with an aperture of 2 metres or more were located in the northern hemisphere. The decision to build the observatory in the southern hemisphere resulted from the necessity of observing the southern sky; some research subjects (such as the central parts of the Milky Way and the Magellanic Clouds) were accessible only from the southern hemisphere.
Director General In office Otto Heckmann 1962–1969 Adriaan Blaauw 1970–1974 Lodewijk Woltjer 1975–1987 Harry van der Laan 1988–1992 Riccardo Giacconi 1993–1999 Catherine Cesarsky 1999–2007 Tim de Zeeuw 2007–2017 Xavier Barcons 2017–2026Andreas Kaufer2026–present Source: www.eso.org, about ESO
It was initially planned to set up telescopes in South Africa where several European observatories were located (Boyden Observatory), but tests from 1955 to 1962 demonstrated that a site in the Andes was preferable: When Jürgen Stock enthusiastically reported his observations from Chile, Otto Heckmann decided to leave the South African project on hold. ESO—at that time about to sign the contracts with South Africa—decided to establish their observatory in Chile. The ESO Convention was signed 5 October 1962 by Belgium, Germany, France, the Netherlands and Sweden. Otto Heckmann was nominated as the organisation's first director general on 1 November 1962. On 15 November 1963 Chile was chosen as the site for ESO's observatory.
A preliminary proposal for a convention of astronomy organisations in these five countries was drafted in 1954. Although some amendments were made in the initial document, the convention proceeded slowly until 1960 when it was discussed during that year's committee meeting. The new draft was examined in detail, and a council member of CERN (the European Organization for Nuclear Research) highlighted the need for a convention between governments (in addition to organisations). The convention and government involvement became pressing due to rapidly rising costs of site-testing expeditions. The final 1962 version was largely adopted from the CERN convention, due to similarities between the organisations and the dual membership of some members.
In 1966, the first ESO telescope at the La Silla site in Chile began operating. Because CERN (like ESO) had sophisticated instrumentation, the astronomy organisation frequently turned to the nuclear-research body for advice and a collaborative agreement between ESO and CERN was signed in 1970. Several months later, ESO's telescope division moved into a CERN building in Geneva and ESO's Sky Atlas Laboratory was established on CERN property. ESO's European departments moved into the new ESO headquarters in Garching (near Munich), Germany, in 1980.
In 2015, Guillem Anglada-Escudé confirmed the existence of Proxima Centauri b at the Southern Observatory.
Member states Country Accession
Chilean observation sites
Although ESO is headquartered in Germany, its telescopes and observatories are in northern Chile, where the organisation operates advanced ground-based astronomical facilities: La Silla, which hosts the New Technology Telescope (NTT) Paranal, where the Very Large Telescope (VLT) is located Llano de Chajnantor, where ALMA, the Atacama Large Millimeter/submillimeter Array, is located
These are among the best locations for astronomical observations in the southern hemisphere. An ESO project is the Extremely Large Telescope (ELT), a 40-metre-class telescope based on a five-mirror design and the formerly planned Overwhelmingly Large Telescope. The ELT will be the largest visible and near-infrared telescope in the world. ESO began its design in early 2006, and aimed to begin construction in 2012. Construction work at the ELT site started in June 2014. As decided by the ESO council on 26 April 2010, a fourth site (Cerro Armazones) is to be home to ELT.
Each year about 2,000 requests are made for the use of ESO telescopes, for four to six times more nights than are available. Observations made with these instruments appear in a number of peer-reviewed publications annually; in 2017, more than 1,000 reviewed papers based on ESO data were published.
ESO telescopes generate large amounts of data at a high rate, which are stored in a permanent archive facility at ESO headquarters. The archive contains more than 1.5 million images (or spectra) with a total volume of about 65 terabytes (65,000,000,000,000 bytes) of data.
+ ESO telescopes Name Short Size Type Location Year ESO 3.6 m telescope ESO 3.6m 3.57 m optical and infrared La Silla 1977 MPG/ESO 2.2 m telescope MPG 2.20 m optical and infrared La Silla 1984 New Technology Telescope NTT 3.58 m optical and infrared La Silla 1989 Very Large Telescope VLT 4 × 8.2 m4 × 1.8 m optical to mid-infrared, array Paranal 1998 Visible and Infrared Survey Telescope for Astronomy VISTA 4.1 m near-infrared, survey Paranal 2009 VLT Survey Telescope VST 2.6 m optical, survey Paranal 2011 Atacama Large Millimeter/submillimeter Array ALMA 50 × 12 m12 × 7 m4 × 12 m millimetre-/submillimetre-wavelengthinterferometer array Chajnantor 2011 Extremely Large Telescope ELT 39.3 m optical to mid-infrared Cerro Armazones End of this decadeALMA is a partnership among Europe, the United States, Canada, East Asia and the Republic of Chile.Additional ESO research facilities are located in Santiago, Chile and include a library, computing resources and programmes for visiting scientists.ESO also maintains close ties with other observatories and universities throughout the country.Source: ESO – Telescopes and Instrumentation
La Silla
La Silla, located in the southern Atacama Desert north of Santiago de Chile at an altitude of , is the home of ESO's original observation site. Like other observatories in the area, La Silla is far from sources of light pollution and has one of the darkest night skies on Earth. In La Silla, ESO operates three telescopes: a 3.6-metre telescope, the New Technology Telescope (NTT) and the 2.2-metre Max-Planck-ESO Telescope.
The observatory hosts visitor instruments, attached to a telescope for the duration of an observational run and then removed. La Silla also hosts national telescopes, such as the 1.2-metre Swiss and the 1.5-metre Danish telescopes.
About 300 reviewed publications annually are attributable to the work of the observatory. Discoveries made with La Silla telescopes include the HARPS-spectrograph detection of the planets orbiting within the Gliese 581 planetary system, which contains the first known rocky planet in a habitable zone outside the solar system. Several telescopes at La Silla played a role in linking gamma-ray bursts, the most energetic explosions in the universe since the Big Bang, with the explosions of massive stars. The ESO La Silla Observatory also played a role in the study of supernova SN 1987A.
ESO 3.6-metre telescope
The ESO 3.6-metre telescope began operations in 1977. It has been upgraded, including the installation of a new secondary mirror. The conventionally designed horseshoe-mount telescope was primarily used for infrared spectroscopy; it now hosts the HARPS spectrograph, used in search of extra-solar planets and for asteroseismology. The telescope was designed for very high long-term radial velocity accuracy (on the order of 1 m/s).
New Technology Telescope
The New Technology Telescope (NTT) is an altazimuth, 3.58-metre Ritchey–Chrétien telescope, inaugurated in 1989 and the first in the world with a computer-controlled main mirror. The flexible mirror's shape is adjusted during observation to preserve optimal image quality. The secondary mirror position is also adjustable in three directions. This technology (developed by ESO and known as active optics) is now applied to all major telescopes, including the VLT and the future ELT.
The design of the octagonal enclosure housing the NTT is innovative. The telescope dome is relatively small and ventilated by a system of flaps directing airflow smoothly across the mirror, reducing turbulence and resulting in sharper images.
MPG/ESO 2.2-metre telescope
The 2.2-metre telescope has been in operation at La Silla since early 1984, and is on indefinite loan to ESO from the Max Planck Society (, or MPG, in German). Telescope time is shared between MPG and ESO observing programmes, while operation and maintenance of the telescope are ESO's responsibility.
Its instrumentation includes a 67-million-pixel wide-field imager (WFI) with a field of view as large as the full moon, which has taken many images of celestial objects. Other instruments used are GROND (Gamma-Ray Burst Optical Near-Infrared Detector), which seeks the afterglow of gamma-ray bursts—the most powerful explosions in the universe, and the high-resolution spectrograph FEROS (Fiber-fed Extended Range Optical Spectrograph), used to make detailed studies of stars.
Other telescopes
La Silla also hosts several national and project telescopes not operated by ESO. Among them are the Swiss Euler Telescope, the Danish National Telescope and the REM, TRAPPIST and TAROT telescopes.