Observatories Around the World

An observatory is any facility designed to collect and analyze light or other signals from astronomical objects. The oldest continuously operating scientific observatory, the Paris Observatory, was founded in 1667 under King Louis XIV of France, and the Royal Observatory at Greenwich followed in 1675 under King Charles II of England. For most of the subsequent three centuries, observational astronomy meant visible-light observations from ground-based telescopes placed on hills, estates, or university grounds. The twentieth century transformed that tradition. Advances in mirror casting, active optics, adaptive optics, radio electronics, and space flight opened entirely new windows on the universe, and purpose-built facilities were placed on remote mountain peaks, in deep caverns, beneath Antarctic ice, and in Sun-Earth Lagrange orbits where conditions favor the required observations.

Modern observatories are classified first by the wavelength band they observe and then by their location. Optical and near-infrared observatories are generally ground-based and are placed at high altitude in dry, dark, atmospherically stable locations. The four premier optical sites in operation are Mauna Kea in Hawaii, Cerro Paranal and Cerro Tololo in the Chilean Atacama, the Canary Islands peak of Roque de los Muchachos on La Palma, and the desert mountaintops of the American Southwest. Radio observatories require radio-quiet zones but can operate at lower elevations. X-ray and gamma-ray astronomy, whose photons cannot penetrate the atmosphere, is carried out almost entirely from space. A new generation of multi-messenger observatories uses detectors that are sensitive to gravitational waves or high-energy neutrinos rather than electromagnetic radiation.

Observatories are operated by national agencies, multinational consortia, and large university partnerships. In the United States, ground-based astronomy is coordinated primarily through the National Science Foundation and the NOIRLab system. Space-based programs are led by the National Aeronautics and Space Administration (NASA) and, in Europe, by the European Space Agency (ESA). The European Southern Observatory (ESO), founded in 1962, operates the premier ground-based facilities of the southern hemisphere and is jointly supported by sixteen member states. Japan's National Astronomical Observatory (NAOJ), the CSIRO in Australia, the Chinese Academy of Sciences, and other national bodies operate complementary facilities. A growing number of major projects, including the Atacama Large Millimeter Array and the Square Kilometre Array, are organized as transnational scientific partnerships.

The modern institutional observatory is a seventeenth-century innovation. The Paris Observatory, commissioned in 1667 by King Louis XIV at the urging of the Académie royale des sciences, and the Royal Observatory at Greenwich, founded in 1675 to support maritime navigation, established the template of a state-funded observatory with a permanent staff, published observations, and close ties to the scientific academies. Russia's Pulkovo Observatory, founded in 1839 outside Saint Petersburg, became the most important astronomical institution of the nineteenth century and set new standards for precision astrometry. The United States Naval Observatory, founded in 1830, joined a growing roster of national observatories whose original purpose was the provision of timekeeping and nautical almanacs rather than purely scientific research.

The late nineteenth and early twentieth centuries brought a series of landmark refracting and reflecting telescopes. The 40-inch (1.02-meter) refractor installed at Yerkes Observatory in Williams Bay, Wisconsin, in 1897 remains the largest refracting telescope ever built for astronomical use. The 100-inch (2.54-meter) Hooker Telescope, completed at Mount Wilson Observatory in southern California in 1917, was the world's largest operating telescope for thirty-one years and was the instrument with which Edwin Hubble demonstrated in the 1920s that the Milky Way is one of many galaxies and that those galaxies are receding from one another, the observation that underlies the modern expanding-universe cosmology. In 1948 the 200-inch (5.1-meter) Hale Telescope at Palomar Observatory, also in southern California, succeeded the Hooker as the world's largest effective telescope and held that title until the first Keck Telescope saw first light in 1990.

The second half of the twentieth century saw the emergence of purpose-built international observatories on high, dry sites. The Kitt Peak National Observatory in Arizona (1958), the Cerro Tololo Inter-American Observatory in Chile (1962), the Mauna Kea Observatories in Hawaii (1970), and the Observatorio del Roque de los Muchachos in the Canary Islands (1985) all grew into major multi-telescope campuses. The launches of the Einstein Observatory in 1978, the Infrared Astronomical Satellite in 1983, and above all the Hubble Space Telescope in 1990 opened wavelength bands that the atmosphere blocks and marked astronomy's decisive move into space.

Placing a telescope in orbit removes the blurring effects of the atmosphere and opens wavelength bands that are otherwise absorbed by the air. Ultraviolet, X-ray, and gamma-ray astronomy are possible only from space. Infrared astronomy is also much more productive above the atmosphere, because the atmosphere and the telescope itself both radiate in the infrared and drown out faint celestial sources. The space-based fleet now includes roughly two dozen operational major observatories distributed across the electromagnetic spectrum.

The Hubble Space Telescope, launched on April 24, 1990 aboard Space Shuttle Discovery, is a 2.4-meter ultraviolet, optical, and near-infrared observatory in a 540-kilometer low Earth orbit. Its primary mirror was famously ground to the wrong prescription and produced blurred images at launch. A corrective optics package and new instruments installed by astronauts on Servicing Mission 1 in December 1993 restored Hubble's performance, and four subsequent servicing missions extended the telescope's capabilities through at least the late 2020s. Hubble has produced the most widely reproduced astronomical images in history and remains a workhorse of the international astronomical community.

The Chandra X-ray Observatory, launched in July 1999 on Space Shuttle Columbia, is the flagship X-ray observatory of NASA. Its highly elliptical orbit takes it a third of the way to the Moon and allows for long uninterrupted observations. The Spitzer Space Telescope, launched in 2003, operated in the mid- and far-infrared until its helium coolant was exhausted in 2009; it continued in a warmer configuration until the mission was ended in January 2020. NASA's Kepler mission (2009 to 2018) and its successor the Transiting Exoplanet Survey Satellite (TESS, launched 2018) discovered the great majority of the currently catalogued exoplanets through the transit method. The European Space Agency's Gaia mission, launched in 2013, is producing the most precise three-dimensional map of the Milky Way ever made, with astrometric positions and motions for nearly two billion stars.

The James Webb Space Telescope (JWST), launched on an Ariane 5 from French Guiana on December 25, 2021, is the largest and most complex telescope ever sent to space. Its 6.5-meter segmented primary mirror and five-layer sunshield operate at the Sun-Earth L2 Lagrange point, approximately 1.5 million kilometers from Earth, where passive cooling keeps the instruments below fifty kelvin. JWST is optimized for the near-infrared and mid-infrared and is designed to observe the earliest galaxies, stellar nurseries, and exoplanet atmospheres. ESA's Euclid mission, launched in July 2023, is a 1.2-meter wide-field telescope mapping dark energy and dark matter across a third of the sky.

Multi-messenger astronomy uses non-electromagnetic signals, principally gravitational waves and high-energy neutrinos, to study astrophysical sources that are obscured, distant, or otherwise inaccessible to photon-based telescopes. The first direct detection of a gravitational wave was made on September 14, 2015 by the Laser Interferometer Gravitational-Wave Observatory (LIGO), which identified the inspiral and merger of a pair of stellar-mass black holes at a distance of about 1.3 billion light-years. The three LIGO founders received the 2017 Nobel Prize in Physics for that discovery. A joint detection of gravitational waves and electromagnetic radiation from the neutron-star merger GW170817 on August 17, 2017, by LIGO, Virgo, and more than seventy follow-up observatories inaugurated the era of multi-messenger astronomy in full.

LIGO consists of two 4-kilometer Michelson interferometers with Fabry-Pérot cavities in the arms, one at Hanford in Washington State and the other at Livingston in Louisiana. A third comparable instrument, Virgo, with 3-kilometer arms, is operated by the European Gravitational Observatory near Cascina, Italy. The 3-kilometer KAGRA detector near the Kamioka mine in Japan, built inside a granite mountain to reduce seismic noise and using cryogenic mirrors, joined the international network in its third observing run. Together LIGO, Virgo, and KAGRA now publish detections in a continuous observing program under a formal data-sharing agreement.

The IceCube Neutrino Observatory at the Amundsen-Scott South Pole Station in Antarctica instruments one cubic kilometer of the Antarctic ice sheet with 5,160 optical sensors frozen into eighty-six vertical strings at depths between 1,450 and 2,450 meters. High-energy neutrinos that interact in the ice produce charged secondaries whose Cherenkov light is timed and triangulated to reconstruct the neutrino's direction. In 2017 IceCube identified a single high-energy neutrino that, in combination with follow-up observations by gamma-ray, optical, and radio telescopes, was traced to the blazar TXS 0506+056, providing the first identification of an extragalactic source of astrophysical neutrinos. Complementary neutrino facilities are operated at Lake Baikal in Russia and in the Mediterranean Sea (KM3NeT).

Three flagship ground-based optical facilities are either in commissioning or under construction and will define observational astronomy for the next generation. The Vera C. Rubin Observatory, formerly known as the Large Synoptic Survey Telescope, sits on Cerro Pachón in Chile near the existing Gemini South and SOAR telescopes. Its 8.4-meter primary-tertiary mirror and 3.2-gigapixel camera, the largest digital camera ever built for any purpose, will image the entire southern sky approximately every three nights for ten years, producing a time-domain catalog of billions of objects and an unprecedented record of variable and transient phenomena. First light for system verification was achieved in late 2025 and the ten-year Legacy Survey of Space and Time is scheduled to begin in 2026.

The Extremely Large Telescope (ELT) under construction on Cerro Armazones in northern Chile is a project of the European Southern Observatory. With a segmented primary mirror 39.3 meters in diameter, the ELT will have roughly thirteen times the collecting area of any single existing optical telescope. Its adaptive optics system, which uses laser guide stars and thousands of individually controlled mirror actuators, is designed to approach the diffraction limit at visible and near-infrared wavelengths. First light is planned for later this decade. The Giant Magellan Telescope at Las Campanas Observatory in Chile and the Thirty Meter Telescope, whose siting remains under review, are comparable-scale United States-led projects.

In radio astronomy, the Square Kilometre Array (SKA) is the principal international project of the coming decade. Hosted in both South Africa and Australia and coordinated by the SKA Observatory intergovernmental organization headquartered at Jodrell Bank in the United Kingdom, the SKA will eventually comprise thousands of dishes and low-frequency dipole antennas working together. Construction of the first two subarrays, SKA-Mid in the South African Karoo and SKA-Low in Western Australia, began in 2022, with the existing MeerKAT array in South Africa and the Australian SKA Pathfinder (ASKAP) serving as precursors and eventually as integrated components of the larger system. The SKA is designed to study the early universe during the epoch of reionization and to conduct all-sky surveys of the magnetic fields and neutral-hydrogen content of the cosmos.

The performance of a ground-based observatory depends on the quality of the night sky above it, and astronomers have worked for decades to protect observing sites from light pollution, radio frequency interference, and atmospheric contamination. The International Astronomical Union (IAU), through its Commission B7 on Protection of Existing and Potential Observatory Sites and the Dark and Quiet Skies for Science and Society initiative, coordinates international advocacy for the preservation of observatory sites. The IAU works with national and local governments to encourage lighting ordinances that limit outdoor illumination, require shielded fixtures, and favor warm-colored lamps over blue-rich white LEDs that scatter more strongly in the atmosphere. Chile's Ministry of Environment, the Spanish Sky Law of 1988 on La Palma, and the International Dark Sky Reserve designations administered by DarkSky International are all examples of successful implementations.

Radio observatories require a different form of protection. The United States National Radio Quiet Zone, established by the Federal Communications Commission and the Interdepartmental Radio Advisory Committee in 1958, covers approximately 33,700 square kilometers of West Virginia and Virginia and restricts fixed and mobile radio transmissions in a ten-mile core around the Green Bank site. The Murchison Radio-astronomy Observatory in Western Australia, where the SKA-Low array is being built, is similarly protected by an Australian Radio Quiet Zone. The International Telecommunication Union has reserved a number of radio frequency bands for radio astronomy use, most notably the 1400 to 1427 MHz band that contains the 21-centimeter hydrogen line.

Since 2019 the rapid proliferation of low Earth orbit satellite constellations, principally SpaceX's Starlink system but including OneWeb, Amazon's Project Kuiper, and Chinese constellations, has introduced a new form of sky contamination. Bright satellite trails in images taken by wide-field optical telescopes such as the Vera Rubin Observatory, and radio emissions from satellite downlinks that interfere with protected astronomical bands, have prompted formal expressions of concern from the IAU, from the American Astronomical Society, and from the United Nations Committee on the Peaceful Uses of Outer Space. SpaceX and several other operators have implemented darkening treatments and sunshade designs to reduce the optical brightness of their satellites. The long-term impact of mega-constellations on ground-based observing is an active area of research and regulatory negotiation.

Detailed citations, data references, and institutional sources for all CountryReports content are listed on the Sources page. The following space agencies, national research councils, observatory consortia, and international scientific unions are the primary authorities we rely on for observatory and telescope content.

Space Agencies and Space Observatories

• NASA — Hubble Space Telescope — Mission pages, servicing-mission histories, and operational status for HST, operated jointly by NASA and ESA.
• NASA — James Webb Space Telescope — Mission overview, instrument documentation, commissioning reports, and science results for JWST.
• Chandra X-ray Observatory (NASA/CfA) — Smithsonian Astrophysical Observatory and NASA Marshall Space Flight Center joint operations of the flagship NASA X-ray observatory.
• Space Telescope Science Institute (STScI) — Science operations center for Hubble, JWST, and the forthcoming Nancy Grace Roman Space Telescope, operated for NASA by the Association of Universities for Research in Astronomy.
• European Space Agency — Space Science — Gaia, Euclid, XMM-Newton, INTEGRAL, and other ESA observatory missions.

Ground-Based Observatory Consortia

• European Southern Observatory (ESO) — Operates the Very Large Telescope at Paranal, the ALMA partnership, and the Extremely Large Telescope at Cerro Armazones. Sixteen member states.
• NSF NOIRLab — U.S. National Science Foundation's coordinated operations of Gemini, Kitt Peak, Cerro Tololo, the Community Science and Data Center, and the forthcoming Vera C. Rubin Observatory.
• National Radio Astronomy Observatory (NRAO) — Operates the Jansky Very Large Array and the Very Long Baseline Array and is the U.S. partner in ALMA. An NSF facility managed by Associated Universities, Inc.
• Green Bank Observatory — Operator of the 100 m by 110 m Robert C. Byrd Green Bank Telescope in the National Radio Quiet Zone.
• National Astronomical Observatory of Japan (NAOJ) — Operator of the 8.2 m Subaru Telescope on Mauna Kea and the Japanese ALMA partnership.
• University of Hawaii — Mauna Kea Observatories — Institute for Astronomy overview of the Mauna Kea campus and its telescope tenants.
• CSIRO Australia Telescope National Facility — Australia's national radio observatory network including the Parkes 64 m, the Australia Telescope Compact Array, and the ASKAP precursor to the SKA.
• National Research Council Canada — CFHT — Canadian operations of the Canada-France-Hawaii Telescope on Mauna Kea.

Multi-Messenger and Next-Generation Facilities

• LIGO Laboratory (Caltech/MIT) — The Laser Interferometer Gravitational-Wave Observatory; Hanford (Washington) and Livingston (Louisiana) detectors funded by the National Science Foundation.
• European Gravitational Observatory — Virgo — Operates the 3 km Virgo interferometer near Cascina, Italy, in scientific partnership with LIGO and KAGRA.
• IceCube Neutrino Observatory — University of Wisconsin-Madison, the observatory's lead institution. One cubic kilometer of instrumented Antarctic ice at the South Pole.
• Vera C. Rubin Observatory — Joint DOE/NSF facility on Cerro Pachón, Chile, conducting the ten-year Legacy Survey of Space and Time.
• SKA Observatory (SKAO) — Intergovernmental organization headquartered at Jodrell Bank, coordinating construction and operations of the Square Kilometre Array in South Africa and Australia.
• South African Radio Astronomy Observatory (SARAO) — Operator of the MeerKAT array and the SKA-Mid precursor site in the Karoo.

International Scientific Unions and Journals

• International Astronomical Union (IAU) — Global professional body for astronomers, responsible for astronomical nomenclature and for the Dark and Quiet Skies initiative.
• The Astronomical Journal (AJ) — Peer-reviewed journal of the American Astronomical Society, published by IOP; observational astronomy and solar-system studies.
• The Astrophysical Journal (ApJ) — Peer-reviewed journal of the American Astronomical Society, published by IOP; primary journal of astrophysical research.
• Astronomy & Astrophysics (A&A) — Peer-reviewed European astronomical journal sponsored by a consortium of national astronomical societies.

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