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The European Southern Observatory (ESO) is an intergovernmental astronomical organization created in 1962, dedicated to astrophysics and the development and operation of telescopes in the Northern Zone of Chile.

Since when does ESO exist?

It seems that the initiative to create a European astronomical observatory arose in 1953, when the German astronomer Walter Baade and the Dutch astronomer Jan Oort discussed this idea with some colleagues.

Soon after, in 1954, twelve astronomers, from six countries, signed a declaration at the University of Leiden, expressing the desire to build a large-diameter telescope in South Africa.

But, previous studies showed that the climate in South Africa was not favorable for this project to come to fruition.

Six years later, in 1960, the attempts focused on the Atacama Desert, one of the driest places on Earth, in Chile, where the skies, the climate and the collaboration of the government were very favorable.

ESO activities
Artistic image of the ESO mission. Credit: ESO

Which countries make up the ESO

In 1962, five countries were the founding members of this organization: Belgium, France, Germany, the Netherlands and Sweden.

Nine other countries soon joined: Austria, the Czech Republic, Denmark,  Finland, Italy, Portugal, Spain, Switzerland and the United Kingdom.

Brazil is in the process of being ratified as the 15th member and the first non-European.

Chile is considered a headquarters member. Considering these two nations, the number of member countries increases to sixteen.

Austria – Belgium – Brazil – Czechia
Chile – Denmark – Finland – France
Germany – Holland – Italy – Portugal
Spain – Sweden – Switzerland – United Kingdom

ESO organization

The official name of ESO is “European Organization for Astronomical Research in the Southern Hemisphere”.

ESO, the European Southern Observatory, is the leading intergovernmental astronomical organization in Europe, and the most productive astronomical observatory in the world.

The annual contribution to ESO from the member states amounts to some 198 million Euros. ESO has around 700 employees.

Its headquarters are in Germany. In addition, it has an office in Santiago de Chile.

ESO also has three observation centers in Chile:
• La Silla,
• Paranal and
• Chajnantor.

ESO projects

Telescopes ESO
Astronomy begins an era of discoveries in Chile. Credit: ESO

Since 1963, ESO has designed, financed and directed the construction and installation of three large observatories dedicated to large optical telescopes.

The objective of these observatories is to provide astronomers with state-of-the-art facilities, allowing them to carry out important scientific discoveries.

ESO operates two observatories in Chile: APEX and La Silla Observatory.

APEX The Pioneer Experiment of Atacama.

APEX is a collaboration between the Max Planck Institute, the OSO Space Observatory and the European Southern Observatory.

It is located in the Llano de Chajnantor, at 5,100 meters high.

The telescope was manufactured by “VERTEX Antennentechnik” in Duisburg, Germany.

APEX has a set of wide-field bolometric cameras and spectrometers that operate in most atmospheric windows, at wavelengths between 0.2 and 1.4 mm.

ESO operates this telescope.

La Silla Observatory

The La Silla Observatory is located on the edge of the Chilean Atacama Desert, located 600 kilometers north of Santiago de Chile, in the southern part of the Atacama Desert and at an altitude of 2,400 meters.

La Silla
La Silla Observatory. Credit: ESO

La Silla has been an emblem of ESO since the 1960s. Here, ESO operates two of the world’s most productive 4-meter optical telescopes.

The 3.58 meter diameter New Technology Telescope (NTT) established new parameters for telescope engineering and design.

The NTT was the first in the world to have a computer-controlled main mirror, a technology developed at ESO and now applied in most of the world’s large telescopes.

The ESO Telescope, with a 3.6 meter primary mirror, today houses the world’s most important extrasolar planet finder: the HARPS instrument (High Precision Radial Velocity Planet Finder), a spectrograph with unmatched precision.

Many of the ESO member states also use the La Silla infrastructures for specific projects.

There are three observatories created by ESO in Chile:

• VLT: which houses four Very Large Telescopes
• ELT: with the Extremely Large Telescope
• ALMA: the largest terrestrial telescope in the world

Very Large Telescope

The VLT project was installed on Cerro Paranal, a 2,635-meter-high mountain in the Atacama desert in Chile.

The place was chosen for its desert climate, in which clear nights abound, and which provides exceptional conditions for astronomical observation.

VLT telescopes, inaugurated between 1998 and 2001, can operate as four independent telescopes or as a single instrument, for very high resolution.

Working together, the four telescopes possess the same light-gathering capacity of a single 16-meter diameter telescope, making them the largest optical instrument in the world.

The VLT3 telescope, at Cerro Paranal, Atacama, Chile. Credit: J.L. Dauvergne & G. Hüdepohl, web

VLT1 (Very Large Telescope, Antu) with diameter of 8.20 m
VLT2 (Very Large Telescope, Kueyen) with diameter of 8.20 m
VLT3 (Very Large Telescope, Melipal) with diameter of 8.20 m
VLT4 (Very Large Telescope, Yepun) with diameter of 8.20 m

Antu: in the Mapuche language it means Sun.
Kueyen: in the Mapuche language it means Moon.
Melipal: in the Mapuche language it is the Southern Cross.
Yepun: in the Mapuche language it designates the star Sirio.

Extremely Large Telescope

One of ESO’s most prominent projects is the European Extremely Large Telescope: ELT (Extremely Large Telescope).

ELT is ESO’s proposal for the new generation of ground-based optical telescopes.

Artist’s impression of the Extremely Large Telescope (ELT). Credit: web “”

In 2011, the governing bodies of the European Southern Observatory (ESO) approved its budget for 2012.

This budget included preparatory work to locate the Extremely Large Telescope (ELT), at Cerro Armazones, in Chile.

Cerro Armazones is a mountain in northern Chile, in a privileged area for optical and infrared astronomy, as it has almost 350 clear nights a year.

Some of the optical components have already been designed. Among them a mirror 40 meters in diameter.

It will be the world’s largest optical-infrared telescope – the world’s largest eye to scan the skies.

The facility is expected to take 11 years to build, from 2014 to 2025.

ALMA telescopes

ALMA is the acronym for “Atacama Large Millimeter / submillimeter Array”.

The set of ALMA telescopes were installed in “El Llano de Chanjnantor”, some 5,000 meters above sea level, in the Andes mountain range, in Chile.

The project has had the effective cooperation of Chile, which also contributed with the transfer of 176,000,000 square meters of land for these facilities.

ALMA telescopes in Atacama, Chile. Credit: NRAO, National Radio Astronomy Observatory.

ALMA is the largest ground-based telescope ever built. Its main array features fifty high-precision antennas, each 12 meters in diameter, which together act as a single telescope: an interferometer.

This is complemented by an additional set of four 12 m diameter antennas; in addition, there are twelve antennas of 7 m in diameter.

ALMA antennas can be configured in different ways. The maximum distances between antennas can range from 150 meters to 16 kilometers.

The project had a cost of 1.400 million dollars and was financed in equal parts by the sponsoring institutions.

On March 13, 2013, ALMA was inaugurated. Currently 250 people work in the ALMA project in Chile and 250 in 17 other countries.