European Southern Observatory

Contents

1. Overview
2. Etymology
3. Cultural Impact

Intergovernmental organization and observatory in Chile

“ESO” redirects here. For other uses, see ESO (disambiguation) . For the European Space Agency, see ESA .

European Organisation for Astronomical Research in the Southern Hemisphere

(L–R): ESO logo; Map of member states

Abbreviation ESO [1] Formation 1962; 63 years ago (1962) May 28 Type Intergovernmental organisation Purpose Astronomy Headquarters Garching , Germany Membership 16 Official language

English, French, German

Director General Xavier Barcons Website www .eso .org Trailer of the European Southern Observatory

The European Organisation for Astronomical Research in the Southern Hemisphere , [2] more commonly and conveniently abbreviated as the European Southern Observatory (ESO), stands as a testament to humanity’s persistent, if occasionally misguided, curiosity about the cosmos. It is an intergovernmental research organisation , a collective effort of 16 member states, pooling resources for the rather ambitious goal of ground-based astronomy . Established in 1962, this organization has, for over six decades, been painstakingly providing astronomers with what are deemed “state-of-the-art” research facilities and, more importantly, privileged access to the enigmatic southern sky. With a workforce exceeding 750 individuals and an annual budget derived from member state contributions hovering around €162 million [3], one might wonder if they’re truly getting their money’s worth, or if the universe is simply humoring them. Conveniently, all its primary observatories are strategically situated in the remote, high-altitude deserts of northern Chile , far from the distracting glow of human civilization.

One must concede, even I, that ESO has indeed been responsible for the construction and operation of some of the planet’s largest and most technologically sophisticated telescopes . This impressive roster includes the 3.6-meter New Technology Telescope (NTT), a veritable trailblazer in the practical application of active optics – a concept that, frankly, should have been obvious from the start. Then there’s the monumental Very Large Telescope (VLT), a complex marvel comprised of four individual 8.2-meter telescopes, complemented by four smaller auxiliary telescopes. These can either function autonomously, each pursuing its own solitary quest, or, with an almost unnerving coordination, combine their efforts to achieve a singular, magnified vision. For those who prefer to observe the universe not with visible light, but in the more esoteric millimeter and submillimeter wavelength ranges, the Atacama Large Millimeter Array (ALMA) exists. It holds the rather grand title of the world’s largest ground-based astronomy project to date, a colossal undertaking completed in March 2013 through a sprawling international collaboration involving Europe (under ESO’s aegis), North America, East Asia, and, naturally, Chile itself [4] [5]. Because, apparently, observing the “cold universe” requires a global village.

Currently, the even more extravagantly named Extremely Large Telescope (ELT) is in the throes of construction. This behemoth is projected to utilize a 39.3-meter-diameter segmented mirror , a design choice necessitated by the sheer scale, and is poised to become the world’s largest optical reflecting telescope. Its expected operational debut is set for the twilight of this current decade, assuming the universe doesn’t throw any unexpected wrenches into humanity’s carefully laid plans. The ELT’s formidable light-gathering power is anticipated to facilitate highly detailed investigations into planets around other stars , the very first luminous objects to coalesce in the universe, the enigmatic supermassive black holes that anchor galaxies, and, of course, the ever-elusive nature and distribution of the dark matter and dark energy which, according to current understanding, imperceptibly dominate the cosmic landscape. A truly ambitious shopping list, if nothing else.

It seems ESO’s observing facilities have not been entirely idle, having been credited with numerous significant astronomical discoveries and the production of several rather thick astronomical catalogues [6]. Among their more notable findings are the detection of the most distant gamma-ray burst ever recorded – a fleeting cosmic scream from the dawn of time – and compelling evidence for a black hole lurking malevolently at the very heart of our own Milky Way galaxy [7] [8]. In 2004, the VLT, with its impressive capabilities, allowed astronomers to capture what was hailed as the first direct image of an extrasolar planet , specifically 2M1207b , engaged in its solitary orbit around a brown dwarf located a rather inconvenient 173 light-years away [9]. Furthermore, the High Accuracy Radial Velocity Planet Searcher (HARPS ) instrument, cunningly installed on the venerable ESO 3.6-meter telescope, has been instrumental in the ongoing discovery of extrasolar planets, including Gliese 581c —which, in a universe of giants, stands out as one of the smallest rocky planets observed beyond our familiar Solar System [10]. One can only imagine the sheer cosmic indifference of these distant worlds.

History

The ESO headquarters in Garching , Germany, in 1997

The same site in 2014, a year after a new extension was built (in the foreground)

The initial, rather audacious notion that European astronomers should collaborate to establish a single, large, collective observatory was first tentatively put forth by Walter Baade and Jan Oort at the esteemed Leiden Observatory in the Netherlands during the spring of 1953 [11]. Oort, clearly a man not easily deterred by the enormity of such a proposition, actively pursued the concept, gathering a select group of astronomers in Leiden on June 21 of that year to deliberate its feasibility. The subject, once broached, seemed to gain momentum, receiving further discussion at the Groningen conference, also in the Netherlands, shortly thereafter. This burgeoning enthusiasm culminated on January 26, 1954, with the signing of an ESO declaration by astronomers representing six European nations, formally expressing their collective desire for the establishment of a joint European observatory in the southern hemisphere [12]. One presumes the ink was barely dry before the practicalities began to loom.

At that specific historical juncture, a rather inconvenient truth existed: all operational reflector telescopes boasting an aperture of two meters or more were exclusively located in the northern hemisphere. This geographical imbalance meant that significant portions of the celestial sphere, particularly the awe-inspiring southern sky, remained largely unexamined by high-resolution instruments. The decision, therefore, to construct the proposed observatory in the southern hemisphere was not merely a whim but a pragmatic necessity, driven by the imperative to access certain crucial research subjects. These included, most notably, the central, dust-obscured regions of the Milky Way galaxy itself, as well as the nearby, irregular Magellanic Clouds —all of which were exclusively observable from southern latitudes [13]. A simple matter of perspective, really.

Director General In office

Otto Heckmann

1962–1969

Adriaan Blaauw

1970–1974

Lodewijk Woltjer

1975–1987

Harry van der Laan

1988–1992

1993–1999

1999–2007

2007–2017

2017–present

Source: www.eso.org , about ESO [14]

Initially, the plan involved setting up these ambitious telescopes in South Africa, a region where several existing European observatories, such as the Boyden Observatory , were already operational. However, a series of meticulous site tests conducted between 1955 and 1962 rather decisively demonstrated that a location within the formidable Andes mountain range of South America offered superior astronomical conditions. When Jürgen Stock , an astronomer with an evidently infectious enthusiasm, reported his highly favorable observations from Chile , Otto Heckmann —then a pivotal figure in the nascent ESO—made the critical decision to suspend the South African project. Consequently, ESO, which was at that very moment on the verge of finalizing contracts with South Africa, pivoted dramatically, opting instead to establish its primary observatory in Chile [15]. The official ESO Convention was subsequently signed on October 5, 1962, by representatives from Belgium, Germany, France, the Netherlands, and Sweden. Otto Heckmann, perhaps as a reward for his decisive pivot, was fittingly nominated as the organization’s inaugural director general on November 1, 1962. A little over a year later, on November 15, 1963, Chile was formally selected as the definitive site for ESO’s flagship observatory [16]. The universe, it seems, waits for no one, least of all for bureaucratic indecision.

Directors general of ESO (from left to right): Lodewijk Woltjer, Harry van der Laan, Catherine Cesarsky, Tim de Zeeuw and Xavier Barcons

A preliminary proposal outlining a convention for astronomy organizations across these five pioneering countries was meticulously drafted in 1954. Despite some amendments being incorporated into the original document, the progression of this convention proved to be a rather glacial affair, slowly inching forward until 1960. It was during that year’s committee meeting that the draft finally garnered serious discussion. A new, more refined version was subjected to detailed scrutiny, and a council member from CERN —the European Organization for Nuclear Research, a body with its own grand ambitions—astutely highlighted the critical need for a formal convention between governments, in addition to the existing agreement between scientific organizations [17]. This, of course, was an inconvenient truth that, once acknowledged, could not be ignored.

The push for a binding convention and direct governmental involvement became increasingly urgent due to the rapidly escalating costs associated with the site-testing expeditions. Astronomical research, it turns out, is not a cheap hobby. The final version of the convention, meticulously crafted in 1962, largely drew inspiration and structural elements from the pre-existing CERN convention. This adoption was a practical choice, given the inherent similarities between the two large-scale scientific organizations and the rather telling fact that some member states held dual membership in both [18]. Efficiency, even in the realm of cosmic discovery, occasionally prevails over pure originality.

In 1966, the first ESO telescope at the now-iconic La Silla site in Chile finally blinked into operation [12]. Given that CERN, much like ESO, possessed sophisticated instrumentation and a wealth of experience in managing complex scientific endeavors, the astronomy organization frequently sought advice from its nuclear-research counterpart. This rather sensible collaboration culminated in a formal agreement between ESO and CERN, signed in 1970. Only a few months later, ESO’s telescope division relocated into a CERN building in Geneva , and ESO’s specialized Sky Atlas Laboratory was established on CERN property [19]. This period of close collaboration, however, was not permanent; ESO’s European departments eventually moved into their own purpose-built new headquarters in Garching (situated near Munich ), Germany, in 1980. A rather long commute, one might observe.

More recently, in 2015, Guillem Anglada-Escudé and his team achieved a significant confirmation: the existence of Proxima Centauri b , a planet orbiting our nearest stellar neighbor, a discovery made possible, in part, by observations from the Southern Observatory. The universe, it seems, is full of real estate.

Member states

Country

Accession [20]

1962

1962

1962

1964

1964

1967

1982

1982

1 January 2001

8 July 2002

1 July 2004

1 July 2006

1 January 2007

1 July 2008

28 October 2014

28 September 2018

Chilean observation sites

Chajnantor (1999)

Paranal (1998)

ELT (2024)

La Silla (1964)

Bolivia

Argentina

Chile

class=notpageimage| Map of Chile with ESO’s four observatories

While the administrative heart of ESO resides in Germany, its instrumental eyes are firmly fixed on the southern sky from northern Chile . This is where the organization meticulously operates its advanced ground-based astronomical facilities, each chosen for its exceptional atmospheric conditions. These sites include:

La Silla : The venerable original site, currently home to the pioneering New Technology Telescope (NTT).
Paranal : The site of the formidable Very Large Telescope (VLT), a complex of instruments dedicated to pushing the boundaries of optical and infrared astronomy.
Llano de Chajnantor : This high-altitude plateau hosts ALMA, the Atacama Large Millimeter/submillimeter Array , an instrument designed to probe the universe in wavelengths unseen by conventional telescopes.

These remote locations are widely recognized as being among the finest on Earth for astronomical observations in the southern hemisphere [21]. The dry, clear, and stable air at these altitudes provides an unparalleled window into the cosmos, making the arduous journey and construction efforts somewhat justifiable. An ongoing, undeniably ambitious ESO project is the aforementioned Extremely Large Telescope (ELT). This formidable 40-meter-class telescope, incorporating an intricate five-mirror design, builds upon the foundational, though ultimately cancelled, concepts of the even more grandly envisioned Overwhelmingly Large Telescope . The ELT is destined to become the world’s preeminent visible and near-infrared telescope. ESO initiated its detailed design phase in early 2006, with an initial target to commence construction in 2012 [22]. Actual construction work at the ELT site finally began in June 2014 [23], a testament to the slow grind of such monumental endeavors. Following a decision by the ESO council on April 26, 2010, a fourth dedicated site, Cerro Armazones , was officially designated as the future home of the ELT [24] [25] [26]. One can only hope the universe appreciates the effort.

Each year, the demand for access to ESO telescopes is rather staggering, with approximately 2,000 requests pouring in, vying for four to six times more observing nights than are actually available. This competitive environment ensures that only the most compelling (or perhaps politically astute) proposals gain access to these coveted instruments. Observations conducted with these facilities consistently culminate in a significant number of peer-reviewed scientific publications annually. To put this into perspective, in 2017 alone, over 1,000 reviewed papers, directly based on data acquired from ESO, were published [27]. A veritable cascade of cosmic insights, if you care for such things.

The sheer volume of data generated by ESO telescopes is, frankly, immense, arriving at a consistently high rate. This deluge of information is meticulously stored in a permanent archive facility located at the ESO headquarters. This digital repository currently safeguards over 1.5 million images (or spectra), accumulating to an approximate total volume of 65 terabytes (that’s 65,000,000,000,000 bytes) of data. One can only imagine the existential dread of the hard drives involved.

ESO telescopes

Name Short Size Type Location Year

ESO 3.6 m telescope – hosting HARPS 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 m 4 × 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 [A] ALMA 50 × 12 m 12 × 7 m 4 × 12 m [28] millimetre-/submillimetre-wavelength interferometer array Chajnantor 2011

Extremely Large Telescope ELT 39.3 m optical to mid-infrared Cerro Armazones [22] End of this decade

A ALMA 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 [29].
ESO also maintains close ties with other observatories and universities throughout the country [30] [31].
Source: ESO – Telescopes and Instrumentation [32]

La Silla

Main article: La Silla Observatory

La Silla cluster of telescopes

La Silla , perched precariously in the southern reaches of the Atacama Desert , approximately 600 kilometers (370 miles) north of Santiago de Chile , at a rather impressive altitude of 2,400 meters (7,900 feet), represents the genesis of ESO’s observational endeavors. Much like its sister observatories scattered across this arid, celestial haven, La Silla benefits immeasurably from its profound isolation from sources of light pollution , offering what are arguably some of the darkest, most pristine night skies on the entire planet [33]. Here, ESO diligently operates three primary telescopes: the venerable 3.6-meter telescope, the innovative New Technology Telescope (NTT), and the 2.2-meter Max-Planck-ESO Telescope.

Beyond these core instruments, the observatory graciously accommodates various “visitor instruments,” which are temporarily affixed to a telescope for the specific duration of an observational run before being unceremoniously detached. Furthermore, La Silla serves as a host for several national telescopes, including the 1.2-meter Swiss telescope and the 1.5-meter Danish telescope, demonstrating a spirit of collaboration that is almost heartwarming.

The scientific output from the work conducted at this observatory is substantial, contributing approximately 300 peer-reviewed publications annually. Among the more significant discoveries attributed to La Silla’s telescopes is the detection, via the HARPS-spectrograph , of multiple planets orbiting within the Gliese 581 planetary system . This particular system, notably, contains the first confirmed rocky planet situated within a star’s “habitable zone” outside our own familiar solar system [34] [35]. A small, potentially life-sustaining rock in the cosmic void – how quaint. Several other telescopes at La Silla also played a crucial, albeit supporting, role in establishing a definitive link between gamma-ray bursts —the most energetic explosions witnessed in the universe since the Big Bang itself—and the cataclysmic explosions of massive stars. Moreover, the ESO La Silla Observatory was instrumental in the detailed study of supernova SN 1987A , a cosmic event that briefly illuminated the southern skies [36].

ESO 3.6-metre telescope

Main article: ESO 3.6 m Telescope

The ESO 3.6 m Telescope

The ESO 3.6-meter telescope , a workhorse of astronomical observation, commenced its operational life in 1977. Since then, it has undergone a series of significant upgrades, including the installation of a new secondary mirror [37], because even the best tools need a little polishing now and then. This conventionally designed horseshoe-mount telescope was initially predominantly employed for infrared spectroscopy . However, its primary function has since evolved, and it now proudly hosts the HARPS spectrograph. This instrument is a dedicated hunter of extra-solar planets , meticulously searching for the tell-tale wobbles in stellar motion, and also contributes to the intricate field of asteroseismology , studying the internal structure of stars through their oscillations. The telescope was specifically engineered to achieve exceptionally high long-term radial velocity accuracy, capable of measurements on the order of a mere 1 meter per second [38]. It seems even stars have their secrets, and we’re just listening in.

New Technology Telescope

Main article: New Technology Telescope

The New Technology Telescope

The New Technology Telescope (NTT) is an altazimuth , 3.58-meter Ritchey–Chrétien telescope , officially inaugurated in 1989. It holds the rather significant distinction of being the first telescope in the world to incorporate a computer-controlled main mirror. This isn’t just a fancy gimmick; the flexible mirror’s shape can be dynamically adjusted during observation, in real-time, to meticulously preserve optimal image quality. Furthermore, the secondary mirror’s position is also precisely adjustable across three axes. This groundbreaking technology, meticulously developed by ESO and now widely recognized as active optics , has since become a fundamental design principle. It is now standard practice for all major telescopes, including the colossal VLT and the eagerly anticipated future ELT [39]. Because, apparently, even mirrors need a bit of guidance to see clearly.

The architectural design of the octagonal enclosure housing the NTT is, for a telescope dome, remarkably innovative. The dome itself is purposefully kept relatively small, and its ventilation system, a series of precisely engineered flaps, is designed to direct airflow smoothly and uniformly across the primary mirror. This ingenious approach effectively minimizes atmospheric turbulence immediately surrounding the telescope, a common impediment to clear viewing, and thus contributes directly to the production of significantly sharper astronomical images [40].

MPG/ESO 2.2-metre telescope

Main article: MPG/ESO telescope

The 2.2-meter telescope has been a steadfast fixture at La Silla since early 1984. This instrument is not, strictly speaking, owned by ESO, but rather operates under an indefinite loan agreement from the illustrious Max Planck Society (Max-Planck-Gesellschaft zur Förderung der Wissenschaften, or MPG, in German). Observational time on this telescope is judiciously divided between MPG and ESO scientific programs, while the day-to-day operation and maintenance of the telescope itself remain firmly under ESO’s responsibility. A shared burden, one might say.

Its suite of instrumentation includes a formidable 67-million-pixel wide-field imager (WFI), boasting a field of view expansive enough to encompass an area as large as the full moon [41]. This instrument has, over the years, captured an impressive collection of images of various celestial objects, from nebulae to galaxies. Other crucial instruments deployed here include GROND (Gamma-Ray Burst Optical Near-Infrared Detector), a specialized tool designed to seek out the elusive afterglows of gamma-ray bursts—those truly cataclysmic and most powerful explosions in the universe [42]. Additionally, the high-resolution spectrograph FEROS (Fiber-fed Extended Range Optical Spectrograph) is utilized for conducting highly detailed studies of individual stars, dissecting their light to reveal their chemical composition, temperature, and motion.

Other telescopes

The Euler Telescope and the ESO 3.6-m Telescope (background) have discovered many exoplanets .

The Rapid Eye Mount telescope

La Silla also generously hosts several national and project-specific telescopes that, while situated on ESO property, are not directly operated by the organization. Among these collaborative instruments are the Swiss Euler Telescope , the Danish National Telescope, and the REM, TRAPPIST, and TAROT telescopes [43]. A veritable gathering of mechanical eyes.

The Euler Telescope is a 1.2-meter instrument meticulously built and operated by the Geneva Observatory in Switzerland. Its primary function is to conduct high-precision radial velocity measurements, a technique predominantly employed in the arduous quest for large extrasolar planets within the southern celestial hemisphere. Its inaugural discovery was a planet gracefully orbiting Gliese 86 [44]. Other observational programs utilizing Euler focus on the study of variable stars , the aforementioned asteroseismology , the fleeting phenomena of gamma-ray bursts, the continuous monitoring of active galactic nuclei (AGN), and the peculiar effects of gravitational lenses [45].
The 1.54-meter Danish National Telescope, a product of Grubb-Parsons , has been diligently in use at La Silla since 1979. This telescope features an off-axis mount, and its optics are designed according to the Ritchey-Chrétien prescription. Due to the inherent characteristics of its mount and the confined space within its dome, it does face certain significant pointing restrictions [46]. A minor inconvenience for a venerable instrument.

Dome of the Danish 1.54-metre telescope that has been in operation at La Silla Observatory since 1979 [47]

The Rapid Eye Mount telescope (REM) is, as its name suggests, a small, quick-reaction automatic telescope, equipped with a primary 60-centimeter (24-inch) mirror. This telescope, mounted on an altazimuth mount , became operational in October 2002. The instrument’s primary directive is to swiftly follow up on the afterglows of GRBs (gamma-ray bursts) initially detected by the Swift Gamma-Ray Burst Mission satellite [43] [48]. Because some cosmic events simply demand immediate attention.
The Belgian TRAPPIST telescope represents a collaborative venture between the University of Liège and the Geneva Observatory. This 0.60-meter telescope is specifically specialized in the study of comets and exoplanets. Notably, it was one of the few telescopes fortunate enough to observe a stellar occultation of the dwarf planet Eris , an observation that intriguingly suggested Eris might be smaller than even Pluto [49]. A universe of endless re-evaluation, it seems.
The Quick-action telescope for transient objects, TAROT , is a remarkably agile optical robotic telescope, capable of orienting itself with exceptional speed to observe a gamma-ray burst from its very inception. Satellites detecting GRBs promptly transmit signals to TAROT, which can then furnish a sub-arc second position, a level of precision that is invaluable to the broader astronomical community. Data gathered from the TAROT telescope also proves immensely useful in meticulously studying the rapid evolution of GRBs, as well as the intricate physics governing the initial fireball and its interaction with the surrounding interstellar material [50]. It operates remotely from the Haute-Provence Observatory in France, a testament to the wonders of remote control.

Paranal

Main article: Paranal Observatory

The Paranal Observatory is dramatically situated atop Cerro Paranal , a formidable peak within the arid expanse of the Atacama Desert in northern Chile. This mountain, reaching an elevation of 2,635 meters (8,645 feet), is located approximately 120 kilometers (75 miles) south of the bustling city of Antofagasta and a mere 12 kilometers (7.5 miles) from the cooling influence of the Pacific coast [51]. A truly isolated, yet strategically vital, location.

The observatory complex boasts seven major telescopes that operate across the visible and infrared light spectrums. These include the four magnificent 8.2-meter (27-foot) telescopes that comprise the Very Large Telescope, the 2.6-meter (8-foot 6-inch) VLT Survey Telescope (VST), and the 4.1-meter (13-foot) Visible and Infrared Survey Telescope for Astronomy (VISTA). In addition to these primary instruments, there are four smaller 1.8-meter (5-foot 11-inch) auxiliary telescopes, strategically arranged to form an array primarily utilized for advanced interferometric observations [52]. In a rather curious interlude, in March 2008, Paranal served as the backdrop for several scenes in the 22nd James Bond film, Quantum of Solace [53] [54]. Because even the pursuit of cosmic truth occasionally requires a touch of cinematic flair.

A 360-degree panoramic view of the southern night sky from Paranal, with telescopes in foreground

Very Large Telescope

Main article: Very Large Telescope

Very Large Telescope (VLT). Complex of four large telescopes and several smaller ones.

VLT Laser Guide Star. The orange laser beam from the telescope is used for adaptive optics .

The crowning jewel of the Paranal facility is undoubtedly the Very Large Telescope (VLT). This intricate system is composed of four nearly identical 8.2-meter (27-foot) Unit Telescopes (UTs), each meticulously equipped with two or three dedicated instruments. These colossal telescopes possess the unique capability of working in concert, either in groups of two or three, to function as a single, colossal interferometer . The ESO Very Large Telescope Interferometer (VLTI) empowers astronomers to discern details up to 25 times finer than what could be achieved with the individual telescopes operating in isolation. This remarkable feat is accomplished by combining the light beams from multiple telescopes within the VLTI through an extraordinarily complex system of mirrors housed in underground tunnels, where the relative light paths must maintain a precision of less than 1/1000th of a millimeter over distances of 100 meters. The VLTI can achieve an astonishing angular resolution measured in milliarcseconds, a feat comparable to the almost absurd ability to resolve the headlights of a car located on the Moon [55]. One wonders if the car is even worth looking at.

The first of the Unit Telescopes achieved its “first light” (the initial capture of an image) in May 1998, and was formally made available to the broader astronomical community on April 1, 1999 [56]. The remaining telescopes followed suit in 1999 and 2000, bringing the VLT to its full operational capacity. To further enhance the VLTI’s capabilities and ensure its accessibility even when the UTs are engaged in other projects, four smaller 1.8-meter Auxiliary Telescopes (ATs) were strategically installed between 2004 and 2007 [57].

The sheer volume of data emanating from the VLT has consistently translated into an impressive scientific output, leading to the publication of, on average, more than one peer-reviewed scientific paper every single day. In 2017 alone, over 600 reviewed scientific papers were published based on VLT data [27]. Among the VLT’s more celebrated scientific achievements are the direct imaging of an extrasolar planet [58], the meticulous tracking of individual stars as they frantically orbit the supermassive black hole nestled at the very center of the Milky Way [59], and the observation of the faint afterglow of the furthest known gamma-ray burst [60].

At the inauguration of Paranal in March 1999, a rather thoughtful gesture was made: names derived from the indigenous Mapuche language were chosen to replace the rather sterile technical designations (UT1–UT4) of the four VLT Unit Telescopes. To involve the local community, an essay contest was organized for schoolchildren in the region, focusing on the cultural significance of these names. This initiative, rather unexpectedly, attracted numerous entries that eloquently explored the rich cultural heritage of ESO’s host country. A 17-year-old adolescent from Chuquicamata , a town near Calama , submitted the winning essay and was justly awarded an amateur telescope during the inauguration ceremony [61]. Consequently, the four unit telescopes, once known as UT1, UT2, UT3, and UT4, are now more poetically referred to as Antu (sun), Kueyen (moon), Melipal (Southern Cross), and Yepun (Evening Star) [62]. There was, however, a slight initial misstep, with Yepun having been originally mistranslated as “Sirius” rather than the more accurate “Venus” [63]. A small human error in a grand cosmic gesture.

Survey telescopes

Enclosure of British developed VISTA

VST seen in the back between VLT’s dome-shaped auxiliary telescopes

The Visible and Infrared Survey Telescope for Astronomy (VISTA) is strategically housed on a peak adjacent to the one that hosts the VLT, allowing it to share the same pristine observational conditions. VISTA’s main mirror, measuring 4.1 meters (13 feet) across, is particularly notable for its highly curved profile, especially considering its size and the stringent quality requirements. The deviations from a perfectly smooth surface on this mirror are astonishingly minute—less than a few thousandths the thickness of a human hair—a level of precision that presented a formidable challenge during its construction and polishing [64].

VISTA was originally conceived and meticulously developed by a consortium of 18 universities in the United Kingdom, spearheaded by Queen Mary, University of London . It was subsequently contributed to ESO as an “in-kind” contribution, forming a crucial part of the UK’s ratification agreement to join ESO. The intricate design and construction phases of the telescope were expertly managed by the Science and Technology Facilities Council’s UK Astronomy Technology Centre (STFC, UK ATC). Provisional acceptance of VISTA was formally granted by ESO at a ceremony in December 2009 at the ESO headquarters in Garching, attended by representatives from Queen Mary, University of London, and STFC. Since that time, the telescope has been diligently operated by ESO [65], consistently capturing images of exceptional quality since it began its operational life [66] [67].

Complementing VISTA is the VLT Survey Telescope (VST), a state-of-the-art 2.6-meter (8-foot 6-inch) instrument. The VST is equipped with OmegaCAM, a truly impressive 268-megapixel CCD camera that boasts an expansive field of view, four times the area of the full moon. Its primary role is to survey the sky in visible light, providing a crucial counterpart to VISTA’s infrared observations. The VST, which commenced operations in 2011, is the product of a collaborative venture between ESO and the Astronomical Observatory of Capodimonte (Naples), a prominent research center affiliated with the Italian National Institute for Astrophysics INAF [68] [69].

The scientific objectives of both VISTA and the VST are remarkably broad, ranging from probing the enigmatic nature of dark energy to diligently assessing the population of potentially hazardous near-Earth objects . Teams of dedicated European astronomers are responsible for conducting these extensive sky surveys; some are designed to cover the vast majority of the southern sky, while others concentrate their efforts on smaller, more focused celestial regions. These two survey telescopes are expected to generate truly prodigious amounts of data; a single image captured by VISTA, for instance, contains 67 megapixels, while images from OmegaCAM on the VST will boast an astounding 268 megapixels. Collectively, the VST and VISTA gather more data every single night than all the other instruments on the VLT combined. This results in the production of over 100 terabytes of data annually [70]. A truly overwhelming amount of information, for those who enjoy such things.

Llano de Chajnantor

Main article: Llano de Chajnantor Observatory

Three ALMA antennas on Chajnantor

ALMA antenna on route to Chajnantor plateau

The Llano de Chajnantor is an extraordinary 5,100-meter-high (16,700-foot) plateau situated deep within the Atacama Desert, approximately 50 kilometers (31 miles) east of the tranquil oasis town of San Pedro de Atacama . This remote site is an astonishing 750 meters (2,460 feet) higher than the celebrated Mauna Kea Observatory and a full 2,400 meters (7,900 feet) higher than the Very Large Telescope on Cerro Paranal . While it is undeniably dry, cold, and profoundly inhospitable to human habitation, these very conditions make it an absolutely superlative location for submillimeter astronomy [71]. The critical factor here is the almost complete absence of water vapor molecules in Earth’s atmosphere at this extreme altitude, as these molecules are notorious for absorbing and attenuating submillimeter radiation . Therefore, an exceptionally dry site is an absolute prerequisite for this specialized form of radio astronomy . The telescopes gracing this desolate, yet scientifically rich, landscape include:

Atacama Cosmology Telescope (ACT; notably, not operated by ESO)
Atacama Pathfinder Experiment (Operated on behalf of the Max Planck Institute for Radio Astronomy (MPIfR))
Atacama Large Millimeter Array
Q/U Imaging Experiment (QUIET; also not operated by ESO)
POLARBEAR (located on the Huan Tran Telescope; yet another not operated by ESO instrument)

ALMA, the Atacama Large Millimeter Array , is a sophisticated telescope system specifically engineered for millimetre and submillimetre astronomy. This particular branch of astronomy represents a relatively unexplored frontier, offering a unique window into a universe that remains stubbornly invisible in the more familiar realms of visible or infrared light. It is, in essence, ideal for scrutinizing the “cold universe”—the light at these wavelengths originates from vast, frigid clouds in interstellar space, existing at temperatures only a few tens of degrees above absolute zero . Astronomers leverage this peculiar light to meticulously investigate the chemical and physical conditions prevalent within these molecular clouds , which are dense regions of gas and cosmic dust where new stars are ceaselessly being born. When viewed in visible light, these stellar nurseries are often shrouded in impenetrable darkness due to the obscuring dust; however, they radiate brilliantly in the millimetre and submillimetre portions of the electromagnetic spectrum . This specific wavelength range is also perfectly suited for studying some of the earliest (and consequently most distant) galaxies in the universe, whose light has been profoundly redshifted into these longer wavelengths as a direct consequence of the universe’s relentless expansion [72] [73]. A cosmic time machine, if you will, but a very cold one.

Atacama Pathfinder Experiment

ESO also hosts the Atacama Pathfinder Experiment , known simply as APEX, and operates it diligently on behalf of the Max Planck Institute for Radio Astronomy (MPIfR). APEX is a single 12-meter (39-foot) diameter telescope, designed to operate efficiently at millimetre and submillimetre wavelengths—the spectral region that bridges the gap between infrared light and traditional radio waves. A useful stepping stone, one might observe.

Atacama Large Millimeter/submillimeter Array

Main article: Atacama Large Millimeter Array

ALMA is a truly monumental astronomical interferometer , initially comprising 66 high-precision antennas, meticulously synchronized to operate across wavelengths ranging from 0.3 to 3.6 millimeters. Its main array will ultimately consist of 50 colossal 12-meter (39-foot) antennas, functioning as a single, virtual interferometer . An additional, more compact array, known as the Morita array, is also available, composed of four 12-meter and twelve 7-meter (23-foot) antennas [74]. The antennas, with their impressive mobility, can be strategically rearranged across the vast desert plateau over distances spanning from a mere 150 meters to an expansive 16 kilometers (9.9 miles), thereby granting ALMA a variable “zoom” capability. This unparalleled flexibility will enable the array to probe the universe at millimetre and submillimeter wavelengths with unprecedented sensitivity and resolution, offering a visual acuity up to ten times sharper than even the celebrated Hubble Space Telescope . These incredibly detailed images will serve as a crucial complement to those obtained with the VLT Interferometer [75]. ALMA represents a truly global collaboration, a testament to shared scientific ambition, involving East Asia (Japan and Taiwan ), Europe (under the banner of ESO), North America (the US and Canada), and, of course, the host nation of Chile.

The scientific directives guiding ALMA are broad and profound, encompassing the study of the very origin and formation of stars, galaxies, and planets through intricate observations of molecular gas and cosmic dust. It also aims to meticulously investigate distant galaxies, peering back towards the very edge of the observable universe, and to scrutinize the faint relic radiation that remains as a ghostly echo from the Big Bang itself [76]. A call for ALMA science proposals was formally issued on March 31, 2011 [77], and the first tentative “early observations” commenced on October 3 of that same year [78] [79]. The universe, it seems, is always ready for its close-up.

Outreach

Artist’s impression of ESO Supernova Planetarium & Visitor Centre [80]

To appease the masses and perhaps justify their rather exorbitant expenditures, outreach activities are diligently carried out by the ESO education and Public Outreach Department (ePOD) [81]. Because even the most profound cosmic truths must be packaged for public consumption.

ePOD, in its infinite wisdom, also manages the ESO Supernova Planetarium & Visitor Centre , a dedicated astronomy center conveniently located at the site of the ESO Headquarters in Garching bei München. This monument to public engagement was inaugurated on April 26, 2018 [82]. One hopes it inspires a modicum of understanding, rather than merely superficial wonder.

Video gallery

ESO’s 50th-anniversary event ( Munich Residenz in Germany, 11 October 2012 )
ESO’s first 50 years of exploring the southern sky
José Manuel Barroso visits the ESO in January 2013.
Tim de Zeeuw talks on ESO and its 50th anniversary.
The temporary office buildings at the ESO headquarters in Garching being dismantled
Timelapses of ESO’s VLT , ALMA and La Silla site