La Silla Observatory

La Silla Observatory

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La Silla Observatory is an astronomical observatory
Astronomy in Chile
Chile can be considered the capital of Astronomy in the world, nowadays it gathers 42% of Astronomy Infrastructure and by 2018 will concentrate the 70% of the global infrastructure of telescopes. In the north of the country, the skies are clean and dry for more than 300 days a year...

 in Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...

 with three telescopes built and operated by the European Southern Observatory
European Southern Observatory
The European Southern Observatory is an intergovernmental research organisation for astronomy, supported by fifteen countries...

 (ESO) organisation, and several others are partly maintained by ESO. The observatory is one of the largest in the Southern Hemisphere and was the first in Chile to be used by ESO.

The La Silla telescopes and instruments are located at the outskirts of the Chilean Atacama Desert, one of the driest and loneliest areas of the world. Like other observatories in this geographical area, La Silla is located far from sources of light pollution and, like the Paranal Observatory
Paranal Observatory
Paranal Observatory is an astronomical observatory located on Cerro Paranal at 2,635 m altitude and operated by the European Southern Observatory. The Very Large Telescope is the largest telescope on Paranal, actually composed of four separate 8.2 m telescopes...

, home to the Very Large Telescope
Very Large Telescope
The Very Large Telescope is a telescope operated by the European Southern Observatory on Cerro Paranal in the Atacama Desert of northern Chile. The VLT consists of four individual telescopes, each with a primary mirror 8.2m across, which are generally used separately but can be used together to...

, it has one of the darkest night skies on the Earth.


Following the decision in 1963 to approve Chile as the site for the ESO observatory, scouting parties were sent to various locations to assess their suitability.
The site that was decided upon was La Silla in the southern part of the Atacama desert, 600 km north of Santiago de Chile and at an altitude of 2400 metres. Besides being government property, it had the added benefits of being in a dry, flat and easily accessible area, yet isolated and remote from any artificial light and dust sources. Originally named the Cinchado, it was renamed La Silla (the saddle in Spanish) after its saddle-like shape.

On October 30, 1964, the contracts were signed and an area of 245 square miles was purchased the following year. During 1965, temporary facilities were erected with living quarters, a workshop and storage area.
The dedication ceremony of the road to the top took place in March 1966, two months after its completion.

On 25 March 1969, the ESO site at La Silla was finally formally inaugurated by President Eduardo Frei Montalva
Eduardo Frei Montalva
Eduardo Frei Montalva was a Chilean political leader of world stature. In his long political career, he was Minister of Public Works, president of his Christian Democratic Party, senator, President of the Senate, and president of Chile from 1964 to 1970...

. With a permanent base of dormitories, workshops, hotels and several functioning telescopes, the observatory was fully operational. The 1 m and 1.5 m telescopes had been erected in the late 1960s, and were joined in 1968 by the Gran Prismo Objectif telescope that had been previously been used in South Africa.

By 1976, the largest telescope planned, the 3.6 m, started operations. It was subsequently to have a 1.4m CAT (Coudé Auxiliary Telescope) attached.

In 1984, the 2.2m telescope began operations, while in March 1989, the 3.5 m New Technology Telescope (NTT) saw "first light".

The program reaches its apex with the installation of the SEST in 1987 (Swedish ESO Submillimetre Telescope), the only large submillimetre telescope in the southern hemisphere, which was a combined project between ESO and the Swedish Natural Science Research Council.

During the end of the century some of the original telescopes were closed-the 1m Schmidt closed in 1998 and the 1.5m in 2002, whilst new equipment owned by various foreign observatories was introduced. A 1m telescope owned by Marseille Observatory opened in 1998, followed by a 1.2m telescope from Geneva Observatory in 2000.


ESO operates three major optical and near infrared telescopes at the La Silla site: the New Technology Telescope (NTT), the 3.6-m ESO Telescope, and the 2.2-m Max-Planck-ESO Telescope.

In addition La Silla hosts several other national and project telescopes: the 1.54-m Danish Telescope, the 1.2-m Leonhard Euler Telescope
Leonhard Euler Telescope
Leonhard Euler Telescope, or Swiss 1.2-m Leonhard Euler Telescope, is a diameter aperture reflecting telescope at the Geneva Observatory at La Silla Observatory. It is use for astronomy, and runs the CORALIE echelle spectrograph to search for planets. Its first planet discovery was of one in orbit...

, the Rapid Eye Mount Telescope and the TAROT Telescope. These telescopes are not operated by ESO and hence do not fall under the responsibility of La Silla Science Operations.

The following telescopes have now been decommissioned:
  • ESO 1.52-metre telescope
  • ESO 1-metre telescope
  • ESO 0.5-metre telescope (now at the Observatorio UC in Santiago, Chile)
  • Swedish–ESO Submillimetre Telescope (SEST), 15-metre
  • Coudé Auxiliary Telescope (CAT), 1.4-metre
  • Grand Prism Objectif (GPO) Telescope
  • Marly 1-metre Telescope
  • Swiss T70 Telescope
  • Dutch 0.9-metre Telescope (National telescope)
  • Danish 0.5-metre Telescope (National telescope)
  • Marseille 0.4-metre Telescope (National telescope)
  • Bochum 0.61-metre Telescope (National telescope)

New Technology Telescope

The ESO New Technology Telescope (NTT) is an Alt-Az, 3.58m Richey-Chretien telescope which pioneered the use of active optics
Active optics
Active optics is a technology used with reflecting telescopes developed in the 1980s, which actively shapes a telescope's mirrors to prevent deformation due to external influences such as wind, temperature, mechanical stress...

. The telescope and its enclosure had a revolutionary design for optimal image quality. NTT saw first light in March 1989.

The telescope chamber is ventilated by a system of flaps which optimize the air flow across the NTT minimizing the dome and mirror seeing
The word seeing can mean more than one thing:* In common usage, the word means visual perception* Astronomical seeing, the blurring effects of air turbulence in the atmosphere...

. To prevent heat input to the building, all motors in the telescope are water cooled and all the electronics boxes are insulated and cooled.

The primary mirror of the NTT is actively controlled to preserve its figure at all telescope positions. The secondary mirror position is also actively controlled in three directions. The optimized airflow, the thermal controls, and the active optics give the excellent image quality of the NTT. Note that the NTT has active instead of adaptive optics: it corrects the defects and deformation of the telescope and mirror, but does not correct the turbulence; it ensures that the optics is always in perfect shape. Together with the thermal control, it allows the NTT to reach the ambient seeing, but it does not improve it.

3.6 m ESO Telescope

This 3.6 m Cassegrain telescope started operations in 1976 and has been constantly upgraded since, including the installation of a new secondary mirror that has kept the telescope in its place as one of the most efficient and productive engines of astronomical research.

The telescope hosts HARPS, the High Accuracy Radial velocity Planet Searcher, the world’s foremost exoplanet hunter. HARPS is a spectrograph with unrivalled precision and is the most successful finder of low-mass exoplanets to date. Since April 2008, HARPS is the only instrument available at the 3.6 m telescope.

2.2 m MPG/ESO 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 (Max Planck Gesellschaft or MPG in German). Telescope time is shared between MPG and ESO observing programmes, while the operation and maintenance of the telescope are ESO’s responsibility.

The telescope hosts three instruments: the 67-million pixel Wide Field Imager with a field of view as large as the full Moon, which has taken many amazing images of celestial objects; GROND, the Gamma-Ray Burst Optical/Near-Infrared Detector, which chases the afterglows of the most powerful explosions in the Universe, known as gamma-ray bursts; and the high-resolution spectrograph, FEROS, used to make detailed studies of stars.

Scientific discoveries

With about 300 refereed publications attributable to the work of the observatory per year, La Silla remains at the forefront of astronomy. La Silla has led to an enormous number of scientific discoveries, including several "firsts". The HARPS spectrograph is the undisputed champion at finding low-mass extrasolar planets. It detected the system around Gliese 581
Gliese 581
Gliese 581 is a red dwarf star with spectral type M3V, located 20.3 light years away from Earth in the constellation Libra. Its estimated mass is about a third of that of the Sun, and it is the 89th closest known star system to the Sun. Observations suggest that the star has at least six planets:...

, which contains what may be the first known rocky planet in a habitable zone, outside the Solar System. Several telescopes at La Silla played a crucial role in linking gamma-ray bursts — the most energetic explosions in the Universe since the Big Bang — with the explosions of massive stars. Since 1987, the ESO La Silla Observatory has also played an important role in the study and follow-up of the nearest recent supernova, SN 1987A.

On February 2, 2011, astronomers using the Wide Field Imager on the 2.2m telescope discovered an unusual pure disk galaxy christened NGC 3621.

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