List of largest optical reflecting telescopes
|The world's largest optical reflecting telescopes with an aperture diameter of larger than 8 meters (hover with mouse over image).|
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 one limit on the light-gathering power and resolution of a reflecting telescope's optical assembly. The mirrors themselves can be larger than the aperture, and telescopes may use aperture synthesis achieved by 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 very high 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 time. Location in the northern or southern hemisphere of the Earth can also limit what part of the sky can be observed.
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, may have a working beam combiner, and can form an image may be ranked by an equivalent aperture to this reported by sources. HET-style or fixed telescopes are ranked by an equivalent aperture also.
|Name||Image||Effective aperture||Mirror type||Nationality / Sponsors||Site||Built|
|Gran Telescopio Canarias (GTC)||10.4 m (409 in)||Segmented, 36||Spain (90%), Mexico, USA||Roque de los Muchachos Obs., Canary Islands, Spain||2006/9|
|Hobby-Eberly Telescope (HET)
11 m × 9.8 m mirror
|10 m (394 in) ||Segmented, 91||USA, Germany||McDonald Observatory, Texas, USA||1997|
|Keck 1||10 m (394 in)||Segmented, 36||USA||Mauna Kea Observatories, Hawaii, USA||1993|
|Keck 2||10 m (394 in)||Segmented, 36||USA||Mauna Kea Observatories, Hawaii, USA||1996|
|Southern African Large Telescope (SALT)
11 m × 9.8 m mirror
|9.2 m (362 in)||Segmented, 91||South Africa, USA, UK, Germany, Poland, New Zealand||South African Astronomical Obs., Northern Cape, South Africa||2005|
|Large Binocular Telescope (LBT)
Phased-array optics for combined 11.9 m
|8.4 m (331 in) × 2||Multiple mirror, 2||USA, Italy, Germany||Mount Graham International Observatory, Arizona, USA||2004|
|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|
|MMT (1 x 6.5 m)||6.5 m (256 in)||Single||USA||F. L. Whipple Obs., Arizona, USA||2000|
|Magellan 1 (Walter Baade)||6.5 m (256 in)||Honeycomb||USA||Las Campanas Obs., Atacama Region, Chile||2000|
|Magellan 2 (Landon Clay)||6.5 m (256 in)||Honeycomb||USA||Las Campanas Obs., Atacama Region, Chile||2002|
|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|
|Hale Telescope (200 inch)||5.08 m (200 in)||Single||USA||Palomar Observatory, California, USA||1948|
|LAMOST (6.67 m × 6.05 m + 5.72 m × 4.40 m corrector; effective aperture 3.6–4.9 m)||4.9 m (193 in) ||Segmented
(37 + 24)
|PRC (China)||Beijing Astronomical Obs., Xinglong, China||2008|
|MMT (original optics: 6 × 1.8 m)
→see above for current 6.5 m mirror
|4.7 m (185 in)
(6×1.8 m) 
|Segmented, 6||USA||F. L. Whipple Obs., Arizona, USA||1979–1998|
|Discovery Channel 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|
|Victor M. Blanco Telescope||4 m (157 in)||Single||USA||Cerro Tololo Inter-American Obs., Coquimbo Region, Chile||1976|
|Nicholas U. Mayall 4 m||4 m (157 in)||Single||USA||Kitt Peak National Obs., Arizona, USA||1973|
|Anglo-Australian Telescope (AAT)||3.89 m (153 in)||Single||Australia, UK||Australian Astronomical Obs., New South Wales, Australia||1974|
|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||White Sands Missile Range, New Mexico, USA||2011|
|Astrophysical Research Consortium (ARC)||3.48 m (137 in)||Single||USA||Apache Point Obs., New Mexico, USA||1994|
|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|
|3 m (118 in)||Liquid||USA||NASA Orbital Debris Obs., New Mexico, USA||1995–2002|
|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 and the MMT replacement mirror. It is currently making the LSST primary mirror and 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.
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.
|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||Art deco dome||1713|
|1917–1948||Hooker (100 inch)||2.54||–||Also used for 1st optical interferometer||1742|
For earlier top telescopes see List of largest optical telescopes historically
Below are selected telescopes that are still in the conceptual/proposed stage or still under construction.
Under construction or planned construction
- European Extremely Large Telescope 39.3 m (first light planned for 2024)
- Thirty Meter Telescope 30 m (construction halted since April 2015 due to a permit dispute; first light was planned for 2022 when construction halted)
- Giant Magellan Telescope 7 × 8.4 m mirrors giving a 24.5 m aperture with 21.4 m light gathering area (first light planned in 2021 and completion in 2025)
- Large Synoptic Survey Telescope 8.4 m (first light planned in 2019 and full operations beginning in 2022)
- James Webb Space Telescope 6.5 m (March 2021 launch planned)
- Pan-STARRS 4 × 1.8 m (2 of 4 complete)
- Magdalena Ridge Observatory Telescope Array 10 × 1.4 m
- Daniel K. Inouye Solar Telescope 4 m (construction started in 2013)
- International Liquid Mirror Telescope 4 m (dome construction in Devasthal, India, started in 2013)
- San Pedro Martir Telescope 6.5 m (completion expected by 2023)
- Iranian National Observatory 3.4 m (first light planned in 2020) 
- Large UV Optical Infrared Surveyor (LUVOIR), a proposed space telescope for launch in the mid 2030s. There are several designs under study with 8–15 m diameter, including the Advanced Technology Large-Aperture Space Telescope (ATLAST) and High-Definition Space Telescope (HDST)
- Chinese Giant Solar Telescope (CGST), an infrared and optical solar telescope, with light-gathering power equivalent to a 5 m diameter aperture 
- Colossus Telescope - proposed 70-80 meter diameter telescope for examining exoplanets (2010s)
- Extremely large telescope
- List of largest optical refracting telescopes
- List of optical telescopes
- List of astronomical interferometers at visible and infrared wavelengths
- List of largest optical telescopes historically
- List of largest optical telescopes in the 20th century
- List of largest optical telescopes in the 19th century
- List of largest optical telescopes in the 18th century
- Strehl ratio
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