This is a list of the highest astronomical observatories in the world, considering only ground-based observatories and ordered by elevation above mean sea level. The main list includes only permanent observatories with facilities constructed at a fixed location, followed by a supplementary list for temporary observatories such as transportable telescopes or instrument packages. For large observatories with numerous telescopes at a single location, only a single entry is included listing the main elevation of the observatory or of the highest operational instrument if that information is available.
History of high altitude astronomical observatories Prior to the late 19th century, almost all astronomical observatories throughout history were located at modest elevations, often close to cities and educational institutions for the simple reason of convenience.Krisciunas (1988), see Chapters 1–5. The British physicist and mathematician Isaac Newton is credited with the realization that high-altitude sites are superior for observation because they provide the "most serene and quiet Air" above the dense, turbulent atmosphere ("grosser Clouds"), thereby reducing star twinkling.
As air pollution from industrialization and light pollution from artificial lighting increased during the Industrial Revolution, astronomers sought observatory sites in remote locations with clear and dark skies, naturally drawing them towards the mountains. The first permanent mountaintop astronomical observatory was the Lick Observatory constructed from 1876 to 1887, at the modest elevation of atop Mount Hamilton in California.Krisciunas (1988), see Chapter 6: Harvard, Lick, Yerkes, and the rise of astrophysics. The first high altitude observatory was constructed atop the Pic du Midi de Bigorre in the French Pyrenees starting in 1878, with its first telescope and dome installed in 1904.Brunier (2005), pp. 20–21. Astronomical observations were also made from Mont Blanc in the late 1800s.
A few other high altitude observatories (such as the Lowell Observatory in Arizona and Sphinx Observatory in Switzerland) were constructed through the first half of the 20th century. However, the two most important and prominent of the early 20th century observatories, Mount Wilson Observatory and Palomar Observatory, were both located on mid-elevation mountaintops of about in southern California.Krisciunas (1988), see Chapter 7: Mt Wilson and Palomar. The stunning successes and discoveries made there using the world's largest telescopes, the 100-inch Hooker Telescope and 200-inch Hale Telescope, spurred the move to ever higher sites for the new generation of observatories and telescopes after World War II, along with a worldwide search for locations which had the best astronomical seeing.
Since the mid-20th century, an increasing number of high altitude observatory sites have been developed at locations around the world, including numerous sites in Arizona, Hawaii, Chile, and the Canary Islands.Zirker (2005), see Chapter 4: The Rise of the Great Centers.Krisciunas (1988), see Chapter 8: The Present. The initial wave of high-altitude sites were mostly in the range, but astronomers soon sought even higher sites above . Among the largest, best developed, and most renowned of these high altitude sites is the Mauna Kea Observatory located near the summit of a volcano on the Island of Hawaii, which has grown to include over a dozen major telescopes during the four decades since it was founded. In the first decade of the 21st century, there has been a new wave of observatory construction at very high altitudes above , with such observatories constructed in India, Mexico, and most notably the Atacama Desert in northern Chile, now the site of several of the world's highest observatories. The scientific benefits of these sites outweigh the numerous logistical and physiological challenges which must be overcome during the construction and operation of observatories in remote mountain locations, even in desert, polar, and tropical island sites which magnify the challenges but confer additional observational advantages.
Sites at high altitude are ideal for optical astronomy and provide optimal seeing, being above a significant portion of the Earth's atmosphere with its associated weather, turbulence, and diminished clarity. In particular, sites on mountaintops within about of the ocean often have excellent observing conditions above a stable inversion layer throughout much of the year.Krisciunas (1988), p. 141. High altitude sites are also above most of atmosphere's water vapor, making them ideal for infrared astronomy and submillimeter astronomy as those wavelengths are strongly absorbed by water vapor. On the other hand, high altitude does not offer as significant an advantage for radio astronomy at longer wavelengths, so relatively few radio telescopes are located at such sites. At the far end of the spectrum, for the extremely short wavelengths of x-ray and gamma ray astronomy, along with high-energy cosmic rays, high altitude observations once again offers significant advantages, enough that many experiments at these wavelengths have been conducted by balloon-borne or even by space telescopes, although a number of high-altitude ground-based sites have also been used. These include the Chacaltaya Astrophysical Observatory in Bolivia, which at was the world's highest permanent astronomical observatory from the time of its construction during the 1940s until surpassed in 2009 by the new University of Tokyo Atacama Observatory, an optical-infrared telescope on a remote mountaintop in Chile.
Highest permanent observatories Permanent observatories above 3,000 m: Observatory Name Elevation Observatory Site Location Coordinates Established Type of Observatory Major Instruments University of Tokyo Atacama Observatory (TAO) Cerro Chajnantor Atacama Desert, Chile 2009 Optical, infrared Chacaltaya Astrophysical Observatory Chacaltaya Andes, Bolivia 1946 Cosmic ray, gamma ray James Ax Observatory Cerro Toco Atacama Desert, Chile 2011 Microwave POLARBEAR Simons Observatory Cerro Toco Atacama Desert, Chile 2007 Microwave Large Aperture Telescope and multiple Small Aperture Telescopes. Former site of the Atacama Cosmology Telescope. Llano de Chajnantor Observatory Llano de Chajnantor Atacama Desert, Chile 1999 Millimeter wave, submillimeter ALMA, APEX, QUIET Shiquanhe Observatory (NAOC Ali Observatory) Shiquanhe, Ngari Plateau Tibet Autonomous Region, China 2011 Optical Large Latin American Millimeter Array (LLAMA) Alto de Chorillos Salta, Argentina Under construction Submillimeter LLAMA, QUBIC Llano de Chajnantor Observatory Pampa La Bola Atacama Desert, Chile 2002 Submillimeter ASTE, NANTEN2 Large Millimeter Telescope Alfonso Serrano Sierra Negra Puebla, Mexico 2006 Microwave Indian Astronomical Observatory Mount Saraswati Hanle, Ladakh, India 2001 Infrared, gamma ray, Optical Himalayan Chandra Telescope, HAGAR Meyer–Womble Observatory Mount Blue Sky Colorado, United States 1996 Optical, Infrared Yangbajing International Cosmic Ray Observatory Yangbajain Tibet Autonomous Region, China 1990 Cosmic ray Mauna Kea Observatory Mauna Kea Hawaii, United States 1967 Optical, infrared, submillimeter Keck, UKIRT, Gemini North, Subaru, JCMT, CSO, SMA, CFHT High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory Sierra Negra Puebla, Mexico 2013 Gamma ray Barcroft Observatory White Mountain Peak California, United States 1976 Infrared, millimeter wave Very Long Baseline Array (VLBA), Mauna Kea Site Mauna Kea Hawaii, United States 1986 Radio telescope Llano del Hato National Astronomical Observatory Llano del Hato Andes, Venezuela 1970s Optical telescope 1-m Askania Schmidt camera, a 65-cm Zeiss refractor, a 1-m Zeiss reflector and a 50-cm Askania double astrograph Iranian National Observatory Mount Gargash Isfahan, Iran 2010s Optical telescope Under Construction Sphinx Observatory Jungfraujoch Bernese Alps, Switzerland 1937 Optical telescope Mauna Loa Observatory Mauna Loa Hawaii, United States 1957 Optical, millimeter wave Mauna Loa Solar Observatory, AMiBA Observatorio Astronómico de Moquegua Cambrune Moquegua, Peru 2022 Optical 1m optical telescope in Astroshell dome Magdalena Ridge Observatory South Baldy New Mexico, United States 1999 Optical, infrared Mount Graham International Observatory Mount Graham Arizona, United States 1993 Optical, submillimeter LBT, HHST, VATT Gornergrat Observatory Gornergrat Pennine Alps, Switzerland 1967 Infrared, submillimeter Gornergrat Infrared Telescope, KOSMA Peak Terskol Observatory Peak Terskol North Caucasus, Russia 1980 Optical 2-m Ritchey-Chretien-Coude Zeiss since 1995, 60-cm Zeiss reflector European Extremely Large Telescope Cerro Armazones Atacama Desert, Chile Under construction Optical, near infrared Haleakala Observatory Haleakala Hawaii, United States 1964 Optical, millimeter wave Pan-STARRS, LCOGT Faulkes Telescope North, AEOS Notre Dame University–Louaize Observatory Mount Lebanon Peak Al-Znanir, Lebanon Not completed Optical telescope Under Construction
Highest temporary observatories
Temporary observatories above 3,000 m: Observatory Name Elevation Observatory Site Location Coordinates Established Type of Observatory Major Instruments Receiver Lab Telescope Cerro Sairecabur Atacama Desert, Chile 2002 Submillimeter, 1–2 THz PLATO (PLATeau Observatory) Dome A East Antarctic Ice Sheet, Antarctica 2008 Optical, submillimeter Concordia Station Dome C East Antarctic Ice Sheet, Antarctica 2005 Optical, infrared, submillimeter
Other important high altitude observatories
This is a selected list of the most important and notable high altitude observatories between 1700 and 3000 m; it is not intended to list all of the numerous observatories worldwide in this elevation range: