This list of the largest optical reflecting telescopes with objective diameters of or greater is sorted by aperture, which is a measure of the light-gathering power and resolution of a reflecting telescope. The mirrors themselves can be larger than the aperture, and some telescopes may use aperture synthesis through interferometry. Telescopes designed to be used as optical astronomical interferometers such as the Keck I and II used together as the Keck Interferometer (up to 85 m) can reach higher resolutions, although at a narrower range of observations. When the two mirrors are on one mount, the combined mirror spacing of the Large Binocular Telescope (22.8 m) allows fuller use of the aperture synthesis.
Largest does not always equate to being the best telescopes, and overall light gathering power of the optical system can be a poor measure of a telescope's performance. Space-based telescopes, such as the Hubble Space Telescope, take advantage of being above the Earth's atmosphere to reach higher resolution and greater light gathering through longer exposure times. Location in the northern or southern hemisphere of the Earth can also limit what part of the sky can be observed, and climate conditions at the observatory site affect how often the telescope can be used each year.
The combination of large mirrors, locations selected for stable atmosphere and favorable climate conditions, and active optics and adaptive optics to correct for much of atmospheric turbulence allow the largest Earth based telescopes to reach higher resolution than the Hubble Space Telescope. Another advantage of Earth based telescopes is the comparatively low cost of upgrading and replacing instruments.
Table of reflecting telescopes Telescopes in this list are ordered by effective optical aperture, given as the diameter of a circle with equivalent collecting area. Aperture has historically been a useful gauge of telescopes' limiting resolution, optical area, physical size, and cost. Multiple mirror or segmented mirror telescopes that are on the same mount and usually form a single combined image are ranked by their equivalent combined aperture. Telescopes that cannot use their entire primary mirror at once (e.g. HET or LAMOST) are listed by their maximum effective aperture. Telescopes that are sometimes used for optical interferometry are listed individually, not as a combined instrument. All telescopes with an effective aperture of at least at visible or near-infrared wavelengths are included; selected smaller telescopes are listed elsewhere.
+Reflecting telescopes Name Image Effective aperture Mirror type Nationality / Sponsors Site First light Large Binocular Telescope (LBT) (combined)SPIE 2006 in Orlando – Proceedings of SPIE conference 6267 on "Ground-based and Airborne Telescopes", "The Large Binocular Telescope", John M. Hill, Richard F. Green and James H. SlagleMultipleTwo mirrors USA, Italy, Germany Mount Graham International Observatory, Arizona, USA 2005 Gran Telescopio Canarias (GTC) Segmented36 hexagonal segments Spain, Mexico, USA Roque de los Muchachos Obs., Canary Islands, Spain 2006 Hobby–Eberly Telescope (HET) (effective) Segmented91 × hexagonal segments forming an 11 m × 9.8 m mirror USA, Germany McDonald Observatory, Texas, USA 1997Aperture increased 2015 Keck 1 Segmented36 hexagonal segments USA Mauna Kea Observatories, Hawaii, USA 1993 Keck 2 Segmented36 hexagonal segments USA Mauna Kea Observatories, Hawaii, USA 1996 Southern African Large Telescope (SALT) (effective) Segmented91 × hexagonal segments forming an 11 m × 9.8 m mirror South Africa, USA, UK, Germany, Poland, New Zealand South African Astronomical Obs., Northern Cape, South Africa 2005 Subaru (JNLT) Single Japan Mauna Kea Observatories, Hawaii, USA 1999 VLT UT1 – Antu Single ESO Countries, Chile Paranal Observatory, Antofagasta Region, Chile 1998 VLT UT2 – Kueyen Single ESO Countries, Chile Paranal Observatory, Antofagasta Region, Chile 1999 VLT UT3 – Melipal Single ESO Countries, Chile Paranal Observatory, Antofagasta Region, Chile 2000 VLT UT4 – Yepun Single ESO Countries, Chile Paranal Observatory, Antofagasta Region, Chile 2001 Gemini North Single USA, UK, Canada, Chile, Australia, Argentina, Brazil Mauna Kea Observatories, Hawaii, USA 1999 Gemini South Single USA, UK, Canada, Chile, Australia, Argentina, Brazil Cerro Pachón (CTIO), Coquimbo Region, Chile 2001 James Webb Space Telescope 6.5 m (256 in) Segmented18 hexagonal segments NASA, ESA, CSA Halo orbit around the Earth-Sun L2 Point 2022 MMT (current optics) Single USA F. L. Whipple Obs., Arizona, USA 2000 Magellan 1 Single USA Las Campanas Obs., Atacama Region, Chile 2000 Magellan 2 Single USA Las Campanas Obs., Atacama Region, Chile 2002 Tokyo Atacama Observatory (TAO)SingleJapanCerro Chajnantor, Atacama Desert, Chile2024 Simonyi Survey Telescope (effective) Combined primary & tertiary mirrorTotal diameter USA Vera C. Rubin Observatory, Coquimbo Region, Chile 2025 BTA-6 Single USSR/Russia Special Astrophysical Obs., Karachay–Cherkessia, Russia 1975 Large Zenith Telescope (LZT) Liquid Canada, France, United States Andersen, Geoff. The Telescope, p. 165 Maple Ridge, British Columbia, Canada 2003Decommissioned 2016 Hale Telescope Single USA Palomar Observatory, California, USA 1949 LAMOST (effective) Segmented37 segments for the 6.67 m × 6.05 m primary and 24 segments for the 5.72 m × 4.40 m corrector; effective aperture 3.6–4.9 m China Beijing Astronomical Obs., Xinglong, China 2008 MMT (original optics) (combined) MultipleSix mirrors USA F. L. Whipple Obs., Arizona, USA 1979Mirrors removed 1998 Lowell Discovery Telescope Single USA Lowell Observatory, Happy Jack, Arizona, USA 2012 William Herschel Telescope Single UK, Netherlands, Spain Roque de los Muchachos Obs., Canary Islands, Spain 1987 SOAR Single USA, Brazil Cerro Pachón (CTIO), Coquimbo Region, Chile 2002 VISTA Single ESO Countries, Chile Paranal Observatory, Antofagasta Region, Chile 2009 Víctor M. Blanco Telescope Single USA Cerro Tololo Inter-American Obs., Coquimbo Region, Chile 1976 International Liquid Mirror Telescope Liquid Belgium, Canada, India, Poland ARIES Devasthal Observatory, Nainital, India 2022 Nicholas U. Mayall 4 m Single USA Kitt Peak National Obs., Arizona, USA 1973 Daniel K. Inouye Solar Telescope Single USA Haleakala Observatory, Hawaii, USA 2019 DAG Telescope Single Turkey Eastern Anatolia Observatory, Erzurum, Turkey 2025 Anglo-Australian Telescope (AAT) Single Australia, UK Australian Astronomical Obs., New South Wales, Australia 1974 United Kingdom Infrared Telescope (UKIRT) Single UK, United States Mauna Kea Observatories, Hawaii, USA 1979 3.67 m AEOS Telescope (AEOS) Single USA Air Force Maui Optical Station, Hawaii, USA 1996 3.6 m Devasthal Optical Telescope (DOT) Single India ARIES Devasthal Observatory, Nainital, India 2016 Telescopio Nazionale Galileo (TNG) Single Italy Roque de los Muchachos Obs., Canary Islands, Spain 1997 New Technology Telescope (NTT) Single ESO countries La Silla Observatory, Coquimbo Region, Chile 1989 Canada-France-Hawaii Telescope (CFHT) Single Canada, France, USA Mauna Kea Observatories, Hawaii, USA 1979 ESO 3.6 m Telescope Single ESO countries La Silla Observatory, Coquimbo Region, Chile 1977 MPI-CAHA 3.5 m Single West Germany, Spain Calar Alto Obs., Almería, Spain 1984 USAF Starfire 3.5 m Single USA Starfire Optical Range, New Mexico, USA 1994 WIYN Telescope Single USA Kitt Peak National Obs., Arizona, USA 1994 Space Surveillance Telescope Single USA, Australia White Sands Missile Range, New Mexico, United StatesRelocated toHarold E. Holt Naval Communication Station, Western Australia, Australia 2011Relocated2020 Astrophysical Research Consortium (ARC) Single USA Apache Point Obs., New Mexico, USA 1994Iranian National Observatory (INO340) SingleIranMount Gargash, Isfahan Province, Iran 2022 Shane Telescope Single USA Lick Observatory, California, USA 1959 NASA Infrared Telescope Facility Single USA Mauna Kea Observatory, Hawaii, USA 1979 NASA-LMT Liquid USA NASA Orbital Debris Obs., New Mexico, USA 1995Decommissioned 2002 For continuation of this list, see List of large optical reflecting telescopes
Chronological list of largest telescopes These telescopes were the largest in the world at the time of their construction, by the same aperture criterion as above.
+Reflecting telescopes (chronologically) Years Largest Name Out In Aperture (m) Area (m2) M1 Mirror Note Altitude (m) 2009–Present Gran Telescopio Canarias 10.4 74 36 × 1.9 m hexagons M1 mirror Segmented mirror 2267 1993–2009 Keck 1 10 76 36 × 1.8 m hexagons M1 mirror Segmented mirror, M1 f/1.75 4145 1976–1993 BTA-6 6 26 605 cm f/4 M1 mirror Mirror replaced twice 2070 1948–1976 Hale (200 inch) 5.1 – 508 cm f/3.3 M1 mirror 1713 1917–1948 Hooker (100 inch) 2.54 – Also used for 1st optical interferometer 1742For earlier entries, see List of largest optical telescopes historically
Future telescopes
Under construction
These telescopes are under construction and will meet the list inclusion criteria once completed:
Extremely Large Telescope, Chile – . Construction began in 2018, first light planned in 2029. Thirty Meter Telescope, Hawaii, USA – . Construction began in 2014 but halted in 2015; it has not resumed. Giant Magellan Telescope, Chile – seven 8.4 m mirrors on a single mount. This provides an effective aperture equivalent to a 21.4 m mirror and the resolving power equivalent to a 24.5 m mirror. First light planned in 2029. San Pedro Martir Telescope, Baja California, Mexico – . First light planned in 2023.Universities in U.S. and Mexico Partner on Telescope Project. Arizona Public Media, 13 November 2017. Magdalena Ridge Observatory Interferometer, New Mexico, USA – An optical interferometer array with ten telescopes. The light gathering power is equivalent to a single aperture. The first telescope was installed in 2016; construction was paused in 2019 due to insufficient funding and resumed in 2021. Timau National Observatory, Indonesia – . Construction expected to be completed by early 2025.
Proposed Selected large telescopes which are in detailed design or pre-construction phases:
Habitable Worlds Observatory (LUVOIR), a proposed space telescope for launch in the early 2040s. MUltiplexed Survey Telescope (MUST), a 6.5 m spectroscopic survey telescope. Chinese Giant Solar Telescope (CGST), an infrared and optical solar telescope, with light-gathering power equivalent to a 5 m diameter aperture.
See also List of largest infrared telescopes List of telescope types Lists of telescopes
References
Further reading
External links List of large reflecting telescopes The World's Largest Optical Telescopes Largest optical telescopes of the world Selected largest telescopes Sidereal Messenger Large refracting telescopes (date 1884)