The European Southern Observatory ( ESO; formally the European Organization for Astronomical Research in the Southern Hemisphere) is an intergovernmental research organisation for astronomy, composed and supported by fifteen countries. Established in 1962 with an objective to provide state-of-the-art facilities and access to the Southern Sky to European astronomers, it is famous for building and operating some of the largest and most technologically advanced telescopes in the world, such as the New Technology Telescope (NTT), the telescope that pioneered active optics technology, and the VLT (Very Large Telescope), consisting of four 8-meter class telescopes and four 1.8-m Auxiliary Telescopes. Its numerous observing facilities have made many astronomical discoveries, and produced several astronomical catalogues. Among the more recent discoveries is the discovery of the farthest gamma-ray burst and the evidence for a black hole at the centre of our Galaxy, 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 HARPS spectrograph led to the discovery of many other extrasolar planets, including a 5 earth mass planet around a red dwarf, Gliese 581c. The VLT has also discovered the candidate farthest galaxy ever seen by humans, Abell 1835 IR1916.

All its observation facilities are located in Chile (because of the need to study the Southern skies and the unique atmospheric conditions of the Atacama Desert, ideal for astronomy), while the headquarters are located in Garching near Munich, Germany. ESO operates three major observatories in Chile's Atacama desert, one of the driest places on Earth:
  • La Silla Observatory
  • Paranal Observatory, which hosts the Very Large Telescope
  • Llano de Chajnantor Observatory, which hosts the APEX ( Atacama Pathfinder Experiment) submillimetre telescope and where ALMA, the Atacama Large Millimeter Array, is currently under construction in a collaboration between East Asia ( Japan and Taiwan), Europe (ESO), North America ( USA and Canada), and Chile.
One of the most ambitious ESO projects is the European Extremely Large Telescope, a 42-m telescope based on an innovative 5-mirror design, following the concept of an Overwhelmingly Large Telescope (OWL). If built, the E-ELT will be the largest optical/near-infrared telescope in the world. ESO has started in early 2006 the design phase of this telescope with the aim to be able to start construction in 2011. The E-ELT would then be ready by early next decade. Each year, about 2000 proposals are made for the use of ESO telescopes, requesting between four and six times more nights than are available. ESO is one of the most productive ground-based observatories in the world, which annually results in many peer-reviewed publications: in 2009 alone, more than 650 refereed papers based on ESO data were published. Moreover, research articles based on VLT data are in the mean quoted twice as often as the average. The very high efficiency of the ESO's "science machines" now generates huge amounts of data at a very high rate. These are stored in a permanent Science Archive Facility at ESO headquarters. The archive now 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 also hosts the European Coordinating Facility for the Hubble Space Telescope, a collaboration between ESA and NASA. It's a long-term, space-based observatory. The observations are carried out in visible, infrared and ultraviolet light. In many ways Hubble has revolutionised modern astronomy, by not only being an efficient tool for making new discoveries, but also by driving astronomical research in general.

La Silla
La Silla Observatory, 600 km north of Santiago de Chile and at an altitude of 2400 metres, has been an ESO stronghold since the 1960s. Here, ESO operates most of the most productive 4-metre class telescopes in the world. Out of the eighteen telescopes hosted here, three are still operated by ESO for use by the astronomical community:

MPG/ESO 2.2 m 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-Gesellschaft. Telescope time is shared between MPG and ESO observing programmes, while the operation and maintenance of the telescope are ESO’s responsibility. Its instrumentation includes a spectroscope and a wide-field CCD (WFI) imager capable of mapping substantial portions of the sky in a single exposure. In 2007, a third instrument was added, GROND, that takes images simultaneously in seven colours. It will be mostly used to determine distances of gamma-ray burst. Images taken from this telescope are also used in the Euronear project.

ESO 3.6m Telescope
This conventionally designed horseshoe mount telescope, was mostly used for infrared spectroscopy. It now hosts the HARPS spectrograph, the High Accuracy Radial velocity Planet Searcher, the world’s foremost exoplanet hunter. HARPS is devoted to measuring velocities with extreme precision. Values as small as a few cm/s have been obtained. It is thus used especially for the search of extra-solar planets and for asteroseismology. HARPS was used in the discovery of Gliese 581c and Gliese 581d.

New Technology Telescope (NTT)
The ESO New Technology Telescope (NTT) is an Alt-Az, 3.58m Richey-Chretien telescope which pioneered the use of active optics. Although the NTT is almost the same size as the 3.6 m telescope, the use of active optics makes it a higher resolution instrument. The NTT is indeed the first large telescope to be equipped with active optics, a technology developed at ESO, and nowadays used on all major telescopes. The NTT had also, at the time of building, innovative thermal control systems to minimise the telescope and dome seeing.

Other telescopes
Other telescopes present on the La Silla site include three ESO reflectors, two Danish ones, one Dutch refractor, the Swiss Leonard Euler Telescope (1.2m), all in the range from 0.5 to 1.5 meter, and the Swedish SEST, 15-m submillimeter radio telescope. All but the Euler telescope and the Danish 1.54m telescope are now decommissioned.

The main facility at Paranal is The Very Large Telescope (VLT), the flagship facility for European ground-based astronomy at the beginning of the third Millennium. It is the world's most advanced optical instrument, consisting of four near-identical 8.2-m Unit Telescopes, each hosting two or three instruments, making it certainly the most versatile astronomical facility. The telescopes, named Antu, Kueyen, Melipal and Yepun can work together, in groups of two or three, to form a giant 'interferometer', the ESO Very Large Telescope Interferometer, allowing astronomers to see details up to 25 times finer than with the individual telescopes. The light beams are combined in the VLTI using a complex system of mirrors in underground tunnels where the light paths must be kept equal to distances less than 1/1000 mm over a hundred metres. With this kind of precision the VLTI can reconstruct images with an angular resolution of milliarcseconds, equivalent to distinguishing the two headlights of a car at the distance of the Moon. Four 1.8-m Auxiliary Telescopes (ATs) have been added to the VLTI to make it available when the Unit Telescopes are being used for other projects. These ATs were installed between 2004 and 2007. The first of the Unit Telescopes had its First Light in May 1998 and was offered to the astronomical community on 1 April 1999. The other telescopes followed suit in 1999 and 2000, and the VLT is thus fully operational. Statistics show that in 2007, almost 500 refereed scientific papers were published based on VLT data. What do the names of the four Unit Telescopes mean? In March 1999, at the time of the Paranal Inauguration, four meaningful names of objects in the sky in the Mapuche (Mapudungun) language were chosen. This indigeneous people lives mostly in the area south of the Bio-Bio river, some 500 km south of Santiago de Chile. An essay contest was arranged in this connection among schoolchildren of the Chilean II Region of which Antofagasta is the capital to write about the implications of these names. It drew many excellent entries dealing with the rich cultural heritage of ESO's host country. The jury was unanimous in its choice of the winning essay. This was submitted by 17-year old Jorssy Albanez Castilla from Chuquicamata near the city of Calama. She received the prize, an amateur telescope, during the Paranal Inauguration. Thus, the four Unit Telescopes are now known as:
  • ANTU (UT1; The Sun)
  • KUEYEN (UT2; The Moon)
  • MELIPAL (UT3; The Southern Cross)
  • YEPUN (UT4; Venus - as evening star)
Originally translated as "Sirius", it now seems that "YEPUN" actually means "Venus". The VLT has made an undisputed impact on observational astronomy. It is the most productive individual ground-based facility, and results from the VLT have led to the publication of an average of more than one peer-reviewed scientific paper per day. VLT contributes greatly to making ESO the most productive ground-based observatory in the world. The VLT has stimulated a new age of discoveries, with several notable scientific firsts, including the first image of an extrasolar planet ( eso0842), tracking individual stars moving around the supermassive black hole at the centre of the Milky Way ( eso0846), and observing the afterglow of the furthest known Gamma-Ray Burst. The site also houses the 2.5-m VLT Survey Telescope (VST) and the 4-m VISTA (Visible and Infrared Survey Telescope for Astronomy) with wide fields of view for surveying large areas of sky uniformly, in the visible and infrared, respectively. First Light for VISTA occurred in 2009, and it is in full operation since April 1, 2010. In March 2008, Paranal was the location for the filming of several scenes in the 22nd James Bond movie, Quantum of Solace

Llano de Chajnantor
Llano de Chajnantor Observatory is the highest astronomical observatory on Earth, located at an altitude of 5,100 m on the Llano de Chajnantor plateau, in the Chilean Atacama Desert, about 50 kilometers east of San Pedro de Atacama. It is a very dry site - inhospitable to humans - but an excellent site for submillimeter astronomy. Water vapor molecules in Earth's atmosphere absorbs and attenuates submillimeter radiation and thus a dry site is required for this type of radio astronomy. The telescopes that can be found here are:
  • Atacama Pathfinder Experiment ( APEX)
  • Atacama Large Millimeter Array ( ALMA)
  • Cosmic Background Imager (CBI)
ESO operates here the Atacama Pathfinder Experiment telescope, APEX, in collaboration with the Max Planck Institute for Radio Astronomy ( Bonn, Germany) and the Onsala Space Observatory ( Onsala, Sweden). APEX is the largest submillimeter wavelengths telescope operating in the southern hemisphere. It can serve as a pathfinder for ALMA, the Atacama Large Millimeter Array, a revolutionary astronomical interferometer that ESO, together with its international partners, is now building on the Chajnantor plateau. APEX is based on a prototype ALMA antenna, modified to be operated as single dish submillimeter radio telescope. ALMA will be an astronomical interferometer of revolutionary design, composed of 66 high-precision antennas, and operating at wavelengths of 0.3 to 9.6 mm. Its main array will have fifty antennas, 12 meters in diameter, acting together as a single telescope " an interferometer. An additional compact array of four 12-meter and twelve 7-meter antennas will complement this. The antennas can be spread across the desert plateau over distances from 150 meters to 16 kilometers, which will give ALMA a powerful variable "zoom". It will be able to probe the Universe at millimeter and submillimeter wavelengths with unprecedented sensitivity and resolution, with a vision up to ten times sharper than the Hubble Space Telescope, and complementing images made with the VLT Interferometer. A video of an ALMA transporter shows how the antennas are moved.

On 21 June 1953 a shared European Observatory is discussed for the first time at the Groningen conference in the Netherlands, followed on 26 January 1954 by an ESO declaration by leading astronomers from six European countries expressing the wish that a joint European observatory be established in the southern hemisphere. On 05 October 1962 Belgium, West Germany, France, the Netherlands and Sweden sign the ESO convention and starting 01 November 1962 Otto Heckmann becomes the first Director General of ESO, the first of the seven ESO Directors General to date. For a complete history of the European Southern Observatory visit ESO Timeline.

Member states

The Irish Astronomical Association is currently lobbying the Irish Government for membership.

Science with ESO Telescopes

The search for planets outside our Solar System
The search for planets outside our Solar System constitutes a key element of what is possibly the most profound question for humanity: is there life elsewhere in the Universe? ESO's observatories are equipped with a unique arsenal of instruments for finding, studying and monitoring these so-called 'exoplanets'. Using the Very Large Telescope, astronomers were able for the first time to spot the faint glow of a planet outside our Solar System, taking the first ever picture of an exoplanet. This new world is a giant one, some five times more massive than Jupiter. This observation marks a first major step towards one of the most important goals of modern astrophysics: to characterise the physical structure and chemical composition of giant and, eventually, terrestrial-like planets. With HARPS, the High Accuracy Radial velocity Planet Searcher, astronomers discovered no fewer than four planets orbiting a nearby star with masses below that of Neptune, including a two earth-mass planet " the smallest ever discovered " and a seven earth-mass planet that resides in its star's habitable zone. This planet orbits its host star in about 66 days. Astronomers think that this planet is covered by oceans " a waterworld. This discovery marks a groundbreaking result in the search for planets that could support life. Another telescope at La Silla, using an innovative technique known as microlensing, worked as part of a network of telescopes scattered across the globe. This collaboration discovered a new extrasolar planet significantly more Earth-like than any other planet found so far. The planet, which is only about five times as massive as the Earth, circles its parent star in about 10 years, and most certainly has a rocky/icy surface.

The determination of the age of the universe
The Globular Cluster 47 Tu. Astronomers have used the Very Large Telescope to perform a unique measurement that paves the way for an independent determination of the age of the Universe. They measured for the first time the amount of the radioactive isotope uranium-238 in a star that was born when the Milky Way, the galaxy in which we live, was still forming. Like carbon-dating in archaeology, but over much longer timescales, this uranium 'clock' measures the age of the star. It shows that the star is 12.5 billion years old. Since the star cannot be older than the Universe itself, the Universe must be even older than this. This agrees with what we know from cosmology, which gives an age of the Universe of 13.7 billion years. The star, and our Galaxy, must have formed very soon after the Big Bang. Another result pushes astronomical technology to its limits, and throws new light on the earliest times in the Milky Way. Astronomers made the first ever measurement of the beryllium content in two stars in a globular cluster. With this, they studied the early phase between the formation of the very first stars in the Milky Way and those of this stellar cluster. They found that the first generation of stars in the Milky Way galaxy must have formed soon after the end of the ~200 million-year long 'Dark Ages' that followed the Big Bang .

A Black Hole at the Centre of our Galaxy
What lies at the center of the Milky Way? For a long time, astronomers have suspected that a black hole lurks at the heart of our Galaxy, but could not be sure. After 15 years of regular monitoring of the Galactic Centre with ESO telescopes at the La Silla Paranal Observatory, scientists finally obtained conclusive evidence. Stars at the centre of the Milky Way are so densely packed that special imaging techniques such as Adaptive Optics were needed to boost the resolution of the VLT. Astronomers were able to watch individual stars with unprecedented accuracy as they moved around the Galactic Centre. Their paths conclusively showed that they must be orbiting in the immense gravitational grip of a supermassive black hole, almost three million times more massive than our Sun. The VLT observations also revealed flashes of infrared light emerging from the region at regular intervals. Whilst the exact cause of this phenomenon remains unknown, observers have suggested the black hole may be spinning rapidly. Whatever is happening, the black hole's life is not all peace and quiet. Astronomers also use the VLT to peer into the centres of galaxies beyond our own , where they again find clear signs of supermassive black holes . In the active galaxy NGC 1097, they could see with unprecedented detail a complex network of filaments spiralling down to the centre of the galaxy and possibly providing for the first time a detailed view of the channelling process of matter, from the main part of the galaxy down to its very end in the nucleus.

Gamma-Ray Bursts - One of the Most Energetic Phenomena in the Universe
Gamma-Ray Bursts (GRBs) are bursts of highly energetic gamma rays lasting from less than a second to several minutes ”“ the blink of an eye on cosmological timescales. They are known to occur at huge distances from Earth, towards the limits of the observable Universe. The VLT has observed the afterglow of a Gamma-Ray Burst that is the farthest known ever. With a measured redshift of 8.2, the light from this very remote astronomical source has taken more than 13,000 million years to reach us. It is thus seen when the Universe was less than 600 million years old, or less than five per cent its present age. It must have released 300 times as much energy in a few seconds as our Sun will in its entire lifetime of more than 10.000 million years. GRBs are therefore the most powerful explosions in the Universe since the Big Bang . Researchers have tried to discover the nature of these explosions for a long time. Observations show that GRBs come in two types ”“ short-duration (shorter than a few seconds), and long-duration ”“ and it was suspected that two different kinds of cosmic event caused them. In 2003, astronomers using ESO telescopes played a key role in linking long-duration GRBs with the ultimate explosions of massive stars, known as 'hypernovae'. By following the aftermath of an explosion for a whole month, they showed that the light had similar properties to that from a supernova, caused when a massive star explodes at the end of its life . In 2005, ESO telescopes detected, for the first time, the visible light following a short-duration burst. By tracking this light for three weeks, astronomers showed that the short-duration bursts ”“ unlike the long-duration ones ”“ could not be caused by a hypernova. Instead, it is thought that they are caused by the violent mergers of neutron stars or black holes . Observations of Gamma-Ray Burst afterglows were also coordinated between the VLT and the Atacama Pathfinder Experiment (APEX) in order to identify the possible counterpart and its decay at submillimeter wavelengths .

Science Archive and the Digital Universe
Science Archive Science Archive Data The Science Archive Operation Group receives and redistributes ESO and HST data and provides front-line archive user support. About 12 Terabytes (TB) of public data are distributed per year through the ESO archive, following about 10,000 web requests. Additionally, more than 2,000 CDs and DVDs of proprietary data are sent out annually to their respective Principal Investigators for observations made in service mode. The current total archive holding is about 65 TB, with an input rate of about 15 TB per year. This will soon drastically increase by a factor of 10 or so as the Visible and Infrared Survey Telescope for Astronomy (VISTA) with its near infrared camera will alone produce about 150 TB of data each year. ESO's enterprise-class database servers are coordinated between Germany and Chile, and their technology and complexity rivals that of major commercial enterprises such as the international banking community. The Digital Universe Major breakthroughs in telescope, detector, and computer technology now allow astronomical surveys to produce massive amounts of images, spectra, and catalogues. These datasets cover the sky at all wavelengths from gamma- and X-rays, through optical and infrared, to radio waves. Astronomers are developing ways to do new science, by making the huge amount of data in this 'digital Universe' easily ac-cessible. These techniques use the GRID paradigm of distributed computing, with seamless and transparent access to the data through 'Virtual Observatories'. Just as a physical observatory has telescopes, each with unique astronomical instruments, a Virtual Observatory consists of data centres, each with unique collections of astronomical data, soft-ware systems and processing capabilities. This global, community-based initiative is being developed world-wide under the auspices of the International Virtual Observatory Alliance (IVOA) and in Europe under the framework of the EURO-VO project . Virtual Observatories have already proved their effectiveness, for example by discovering 31 new optically faint, obscured quasar candidates in the existing Great Observatories Origins Deep Survey (GOODS) fields, quadrupling the number previously found. The discovery means that surveys of powerful supermassive black holes have so far underestimated their numbers by at least a factor of two, and possibly by up to a factor of five .

Top 10 Astronomical Discoveries at ESO
ESO Top 10 Astronomical Discoveries. Planetary system Gliese 581 Artist's impression Most distant Gamma-ray burst Artist's impression 1. Accelerating Universe Two independent research teams have shown that the expansion of the Universe is accelerating " based on observations of exploding stars with astronomical telescopes at La Silla . 2.First image of an exoplanet The VLT has obtained the first-ever image of a planet outside our Solar System. The 5-Jupiter-mass planet orbits a failed star " a brown dwarf " at a distance of 55 times the mean Earth-Sun distance . 3.Stars orbiting the Milky Way black hole Several of ESO's flagship telescopes were used in a 16-year long study to obtain the most detailed view ever of the surroundings of the monster lurking at the heart of our galaxy " a supermassive black hole . 4.The gamma-ray burst”“supernova connection ESO telescopes have provided definitive proof that long gamma-ray bursts are linked with the ultimate explosion of massive stars, solving a long-time puzzle . 5. The motion of stars in the Milky Way After more than 1000 nights of observations at La Silla, spread over 15 years, astronomers have determined the motions of more than 14 000 Sun-like stars residing in the neighbourhood of the Sun, showing that our home galaxy has led a much more turbulent and chaotic life than previously assumed . 6.Oldest star known in the Milky Way Using ESO's VLT, astronomers have measured the age of the oldest star known in our galaxy, the Milky Way. At 13.2 billion years old, the star was born in the earliest era of star formation in the Universe . 7.Merging neutron star"gamma-ray burst connection A telescope at La Silla was able to observe the visible light from a short gamma-ray burst for the first time, showing that this family of objects most likely originated from the violent collision of two merging neutron stars . 8.Cosmic temperature independently measured The VLT has detected carbon monoxide molecules in a galaxy located almost 11 billion light-years away for the first time, a feat that had remained elusive for 25 years. This has allowed astronomers to obtain the most precise measurement of the cosmic temperature at such a remote epoch . 9.Most distant object measured The Very Large Telescope has obtained the spectral signature of the earliest, most distant known object in the Universe, seen only about 600 million years after the Big Bang . 10.Lightest exoplanet found The HARPS spectrograph helped astronomers discover a system containing the lightest exoplanet " only about twice the mass of our Earth " as well as a planet located within the habitable zone, where liquid water oceans could exist .

Outreach Activities
ESOcast Outreach activities are carried out by the ESO education and Public Outreach Department (ePOD). A wide range of programs and activities are used to meet the specific requirements of television, print and online media, such as press releases and broadcast material for the media. ePOD embraces a multimedia approach to public outreach, as seen in e.g., the ESOcast, the Hubblecast, Facebook pages etc. ePOD produces high-quality printed material such as brochures, books, annual reports, newsletters (Messenger, ST-ECF Newsletter, CAPjournal) posters, etc. In the past some impressive events have come out of the Department, such as the International Year of Astronomy 2009 IYA2009 (with IAU and UNESCO), VLT First Light, Astronomy On-line, and the S-L 9 impact. Also famous educational campaigns such as Venus Transit, Science on Stage and Science in School have come out of the Department. ePOD also organises exhibitions. ePOD has also gathered all its astronomy communication resources in one place in an attempt to offer communicators a range of useful tools and information. A large collection of nice photos can be found in the ESO Public Image Gallery. A series of products are free to download on the website or they can be ordered in "physical form". As part of the Department, European outreach for the NASA/ESA Hubble Space Telescope provides comprehensive information about this telescope and its scientific discoveries. Also the IAU Press Office is hosted as part of the Department. ESOcasts ”“ Making Sense of the Cosmos ESOcast is a video podcast series dedicated to bringing the latest news and research from ESO ”“ Astronomy made on planet Earth. Here the Universe's ultimate frontier is explored with Doctor J, a.k.a. Dr. Joe Liske who is a German astronomer at ESO. His scientific interests are in cosmology, particularly on galaxy evolution and quasars. ESO Picture of the Week Every week ESO highlights a picture either astronomical, or related to ESO's activities. All former entries are available on the website. These images are among top 10 from ESO Top 100 Images. VISTA's infrared view of the Orion Nebula Member country Joined Belgium 1962 Germany 1962 France 1962 Netherlands 1962 Sweden 1962 Denmark 1967 Switzerland 1981 Italy 1982, 24 May Portugal 2000, 27 June United Kingdom 2002, 8 July Finland 2004, 1 July Spain 2006, 1 July Czech Republic 2007, 1 January Austria 2008, 1 July Brazil 2010, 29 December (Formal accession agreement) ESO General Directors Otto Heckmann 1962”“1969 Adriaan Blaauw 1970”“1974 Lodewijk Woltjer 1975”“1987 Harry van der Laan 1988”“1992 Riccardo Giacconi ( Nobel Prize winner) 1993”“1999 Catherine Cesarsky 1999”“2007 Tim de Zeeuw from 2007 The Helix Nebula The Globular Cluster Omega Centauri A 340-million pixel starscape from Paranal NGC 2264 and the Christmas Tree cluster The Centre of the Milky Way NGC 2467 and Surroundings The Horsehead Nebula Messier 78: a reflection nebula in Orion Panoramic view of the WR 22 and Eta Carinae regions of the Carina Nebula

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