# List of largest optical reflecting telescopes

This list of the largest optical reflecting telescopes with objective diameters of 3.0 metres (120 in) 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

This list is ordered by optical aperture, which has historically been a useful gauge of limiting resolution, optical area, physical size, and cost. Multiple mirror telescopes that are on the same mount and can form a single combined image are ranked by their equivalent aperture. Fixed altitude telescopes (e.g. HET) are also ranked by their equivalent aperture. All telescopes with an effective aperture of at least 3.00 metres (118 in) at visible or near-infrared wavelengths are included.
Reflecting telescopes :
| Name | Effective aperture | Mirror type | Nationality / Sponsors | Site | First light |
| Large Binocular Telescope (LBT) | 11.9 m (469 in) (combined) | Multiple Two 8.4 m (331 in) mirrors | USA, Italy, Germany | Mount Graham International Observatory, Arizona, USA | 2005 |
| Gran Telescopio Canarias (GTC) | 10.4 m (409 in) | Segmented 36 hexagonal segments | Spain, Mexico, USA | Roque de los Muchachos Obs., Canary Islands, Spain | 2006 |
| Hobby–Eberly Telescope (HET) | 10 m (394 in) (effective) | Segmented 91 × 1 m (39 in) hexagonal segments forming an 11 m × 9.8 m mirror | USA, Germany | McDonald Observatory, Texas, USA | 1997 Aperture increased 2015 |
| Keck 1 | 10 m (394 in) | Segmented 36 hexagonal segments | USA | Mauna Kea Observatories, Hawaii, USA | 1993 |
| Keck 2 | 10 m (394 in) | Segmented 36 hexagonal segments | USA | Mauna Kea Observatories, Hawaii, USA | 1996 |
| Southern African Large Telescope (SALT) | 9.2 m (362 in) (effective) | Segmented 91 × 1 m (39 in) 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) | 8.2 m (323 in) | Single | Japan | Mauna Kea Observatories, Hawaii, USA | 1999 |
| VLT UT1 – Antu | 8.2 m (323 in) | Single | ESO Countries, Chile | Paranal Observatory, Antofagasta Region, Chile | 1998 |
| VLT UT2 – Kueyen | 8.2 m (323 in) | Single | ESO Countries, Chile | Paranal Observatory, Antofagasta Region, Chile | 1999 |
| VLT UT3 – Melipal | 8.2 m (323 in) | Single | ESO Countries, Chile | Paranal Observatory, Antofagasta Region, Chile | 2000 |
| VLT UT4 – Yepun | 8.2 m (323 in) | Single | ESO Countries, Chile | Paranal Observatory, Antofagasta Region, Chile | 2001 |
| Gemini North (Gillett) | 8.1 m (319 in) | Single | USA, UK, Canada, Chile, Australia, Argentina, Brazil | Mauna Kea Observatories, Hawaii, USA | 1999 |
| Gemini South | 8.1 m (319 in) | Single | USA, UK, Canada, Chile, Australia, Argentina, Brazil | Cerro Pachón (CTIO), Coquimbo Region, Chile | 2001 |
| James Webb Space Telescope | 6.5 m (256 in) | Segmented 18 hexagonal segments | NASA, ESA, CSA | Halo orbit around the Earth-Sun L2 Point | 2022 |
| MMT (current optics) | 6.5 m (256 in) | Single | USA | F. L. Whipple Obs., Arizona, USA | 2000 |
| Magellan 1 (Walter Baade) | 6.5 m (256 in) | Single | USA | Las Campanas Obs., Atacama Region, Chile | 2000 |
| Magellan 2 (Landon Clay) | 6.5 m (256 in) | Single | USA | Las Campanas Obs., Atacama Region, Chile | 2002 |
| Tokyo Atacama Observatory (TAO) | 6.5 m (256 in) | Single | Japan | Cerro Chajnantor, Atacama Desert, Chile | 2024 |
| BTA-6 | 6 m (236 in) | Single | USSR/Russia | Special Astrophysical Obs., Karachay–Cherkessia, Russia | 1975 |
| Large Zenith Telescope (LZT) | 6 m (236 in) | Liquid | Canada, France, United States | Maple Ridge, British Columbia, Canada | 2003 Decommissioned 2016 |
| Hale Telescope | 5.08 m (200 in) | Single | USA | Palomar Observatory, California, USA | 1949 |
| LAMOST | 4.9 m (193 in) (effective) | Segmented 37 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) (see above for current version) | 4.7 m (185 in) (combined) | Multiple Six 1.8 m (71 in) mirrors | USA | F. L. Whipple Obs., Arizona, USA | 1979 Mirrors removed 1998 |
| Lowell Discovery Telescope | 4.3 m (169 in) | Single | USA | Lowell Observatory, Happy Jack, Arizona, USA | 2012 |
| William Herschel Telescope | 4.2 m (165 in) | Single | UK, Netherlands, Spain | Roque de los Muchachos Obs., Canary Islands, Spain | 1987 |
| SOAR | 4.1 m (161 in) | Single | USA, Brazil | Cerro Pachón (CTIO), Coquimbo Region, Chile | 2002 |
| VISTA | 4.1 m (161 in) | Single | ESO Countries, Chile | Paranal Observatory, Antofagasta Region, Chile | 2009 |
| Víctor M. Blanco Telescope | 4 m (157 in) | Single | USA | Cerro Tololo Inter-American Obs., Coquimbo Region, Chile | 1976 |
| International Liquid Mirror Telescope | 4 m (157 in) | Liquid | Belgium, Canada, India, Poland | ARIES Devasthal Observatory, Nainital, India | 2022 |
| Nicholas U. Mayall 4 m | 4 m (157 in) | Single | USA | Kitt Peak National Obs., Arizona, USA | 1973 |
| Daniel K. Inouye Solar Telescope | 4 m (157 in) | Single | USA | Haleakala Observatory, Hawaii, USA | 2019 |
| Anglo-Australian Telescope (AAT) | 3.89 m (153 in) | Single | Australia, UK | Australian Astronomical Obs., New South Wales, Australia | 1974 |
| United Kingdom Infrared Telescope (UKIRT) | 3.8 m (150 in) | Single | UK, United States | Mauna Kea Observatories, Hawaii, USA | 1979 |
| 3.67 m AEOS Telescope (AEOS) | 3.67 m (144 in) | Single | USA | Air Force Maui Optical Station, Hawaii, USA | 1996 |
| 3.6 m Devasthal Optical Telescope (DOT) | 3.6 m (142 in) | Single | India | ARIES Devasthal Observatory, Nainital, India | 2016 |
| Telescopio Nazionale Galileo (TNG) | 3.58 m (141 in) | Single | Italy | Roque de los Muchachos Obs., Canary Islands, Spain | 1997 |
| New Technology Telescope (NTT) | 3.58 m (141 in) | Single | ESO countries | La Silla Observatory, Coquimbo Region, Chile | 1989 |
| Canada-France-Hawaii Telescope (CFHT) | 3.58 m (141 in) | Single | Canada, France, USA | Mauna Kea Observatories, Hawaii, USA | 1979 |
| ESO 3.6 m Telescope | 3.57 m (141 in) | Single | ESO countries | La Silla Observatory, Coquimbo Region, Chile | 1977 |
| MPI-CAHA 3.5 m | 3.5 m (138 in) | Single | West Germany, Spain | Calar Alto Obs., Almería, Spain | 1984 |
| USAF Starfire 3.5 m | 3.5 m (138 in) | Single | USA | Starfire Optical Range, New Mexico, USA | 1994 |
| WIYN Telescope | 3.5 m (138 in) | Single | USA | Kitt Peak National Obs., Arizona, USA | 1994 |
| Space Surveillance Telescope | 3.5 m (138 in) | Single | USA, Australia | White Sands Missile Range, New Mexico, United States Relocated to Harold E. Holt Naval Communication Station, Western Australia. | 2011 Relocated 2020 |
| Astrophysical Research Consortium (ARC) | 3.48 m (137 in) | Single | USA | Apache Point Obs., New Mexico, USA | 1994 |
| Iranian National Observatory (INO340) | 3.4 m (130 in) | Single | Iran | Mount Gargash, Isfahan Province, Iran | 2022 |
| Shane Telescope | 3.05 m (120 in) | Single | USA | Lick Observatory, California, USA | 1959 |
| NASA Infrared Telescope Facility | 3.0 m (118 in) | Single | USA | Mauna Kea Observatory, Hawaii, USA | 1979 |
| NASA-LMT | 3 m (118 in) | Liquid | USA | NASA Orbital Debris Obs., New Mexico, USA | 1995 Decommissioned 2002 |
| For continuation of this list, see List of large optical reflecting telescopes |||||||
There are only a few sites capable of polishing the mirrors for these telescopes. SAGEM in France polished the four VLT mirrors, the two Gemini mirrors, and the 36 segments for GTC. The Steward Observatory Mirror Lab cast and polished the two LBT mirrors, the two Magellan mirrors, the MMT replacement mirror, and the LSST primary/tertiary mirror. It is currently making the mirrors for the Giant Magellan Telescope. The Keck segments were made by Schott AG. The SALT and LAMOST segments were cast and polished by LZOS. The mirror for Subaru was cast by Corning and polished at Contraves Brashear Systems in Pennsylvania, USA.
This table does not include all the largest mirrors manufactured. The Steward Observatory Mirror Lab produced the 6.5 metre f/1.25 collimator used in the Large Optical Test and Integration Site of Lockheed Martin, used for vacuum optical testing of other telescopes.
Segmented mirrors are also referred to as mosaic mirrors. Single mirrors are also referred to monolithic mirrors, and can be sub-categorized in types, such as solid or honeycomb.

## 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 | Aperture (m) | Area (m$^2$) | 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 | Art deco dome | 1713 |
| 1917–1948 | Hooker (100 inch) | 2.54 | – | | Also used for 1st optical interferometer | 1742 |
| For 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 – 39.3 m (1,550 in). Construction began in 2018, first light planned in 2028.
* Thirty Meter Telescope, Hawaii, USA – 30 m (1,200 in). Construction began in 2014 but halted in 2015; as of 2022 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.
* Vera C. Rubin Observatory, Chile – 8.4 m (330 in). First light planned in 2025.
* San Pedro Martir Telescope, Baja California, Mexico – 6.5 m (260 in). First light planned in 2023.
* Magdalena Ridge Observatory Interferometer, New Mexico, USA – An optical interferometer array with ten 1.4 m (55 in) telescopes. The light gathering power is equivalent to a 4.4 m (170 in) single aperture. The first telescope was installed in 2016; construction was paused in 2019 due to insufficient funding and has not resumed.
* Timau National Observatory, Indonesia – 3.8 m (150 in). Construction expected to be completed by early 2025.

### Proposed

Selected large telescopes which are in detailed design or pre-construction phases:
* Large UV Optical Infrared Surveyor (LUVOIR), a proposed space telescope for launch in the mid 2030s.
* 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.
* Advanced Liquid-mirror Probe of Astrophysics, Cosmology and Asteroids (ALPACA), a proposed Earth-based 8 metre telescope, by Arlin Crotts of Columbia University.