This list of the largest optical reflecting telescopes with objective diameters of 3m (10feet) 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.[1] Another advantage of Earth based telescopes is the comparatively low cost of upgrading and replacing instruments.
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 3m (10feet) at visible or near-infrared wavelengths are included.
| Name | Image | data-sort-type="number" | Nationality / Sponsors | Site | |||
|---|---|---|---|---|---|---|---|
| Large Binocular Telescope (LBT) | 11.9sigfig=3NaNsigfig=3 (combined)[2] | Multiple Two 8.4sigfig=3NaNsigfig=3 mirrors | USA, Italy, Germany | Mount Graham International Observatory, Arizona, USA | 2004 | ||
| Gran Telescopio Canarias (GTC) | 10.4sigfig=3NaNsigfig=3 | Segmented 36 hexagonal segments | Roque de los Muchachos Obs., Canary Islands, Spain | 2006 | |||
| Hobby–Eberly Telescope (HET) | 10sigfig=3NaNsigfig=3 (effective) [3] | Segmented 91 × 1sigfig=2NaNsigfig=2 hexagonal segments forming an 11 m × 9.8 m mirror | USA, Germany | McDonald Observatory, Texas, USA | 1997 Aperture increased 2015 | ||
| Keck 1 | 10sigfig=3NaNsigfig=3 | Segmented 36 hexagonal segments | Mauna Kea Observatories, Hawaii, USA | 1993 | |||
| Keck 2 | 10sigfig=3NaNsigfig=3 | Segmented 36 hexagonal segments | Mauna Kea Observatories, Hawaii, USA | 1996 | |||
| Southern African Large Telescope (SALT) | 9.2sigfig=3NaNsigfig=3 (effective)[4] | Segmented 91 × 1sigfig=2NaNsigfig=2 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) | 8.2sigfig=3NaNsigfig=3 | Single | Japan | Mauna Kea Observatories, Hawaii, USA | 1999 | ||
| VLT UT1 – Antu | 8.2sigfig=3NaNsigfig=3 | Single | Paranal Observatory, Antofagasta Region, Chile | 1998 | |||
| VLT UT2 – Kueyen | 8.2sigfig=3NaNsigfig=3 | Single | Paranal Observatory, Antofagasta Region, Chile | 1999 | |||
| VLT UT3 – Melipal | 8.2sigfig=3NaNsigfig=3 | Single | Paranal Observatory, Antofagasta Region, Chile | 2000 | |||
| VLT UT4 – Yepun | 8.2sigfig=3NaNsigfig=3 | Single | Paranal Observatory, Antofagasta Region, Chile | 2001 | |||
| Gemini North | 8.1sigfig=3NaNsigfig=3 | Single | Mauna Kea Observatories, Hawaii, USA | 1999 | |||
| Gemini South | 8.1sigfig=3NaNsigfig=3 | Single | 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) | 6.5sigfig=3NaNsigfig=3 | Single | F. L. Whipple Obs., Arizona, USA | 2000 | |||
| Magellan 1 [5] | 6.5sigfig=3NaNsigfig=3 | Single | Las Campanas Obs., Atacama Region, Chile | 2000 | |||
| Magellan 2 | 6.5sigfig=3NaNsigfig=3 | Single | Las Campanas Obs., Atacama Region, Chile | 2002 | |||
| Tokyo Atacama Observatory (TAO) | 6.5sigfig=3NaNsigfig=3 | Single | Japan | Cerro Chajnantor, Atacama Desert, Chile | 2024[6] | ||
| 6sigfig=3NaNsigfig=3 | Single | USSR/Russia | Special Astrophysical Obs., Karachay–Cherkessia, Russia | 1975 | |||
| Large Zenith Telescope (LZT) | 6sigfig=3NaNsigfig=3 | Canada, France, United States [7] | Maple Ridge, British Columbia, Canada | 2003 Decommissioned 2016 | |||
| 200inches | Single | Palomar Observatory, California, USA | 1949 | ||||
| 4.9sigfig=3NaNsigfig=3 (effective)[8] | 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[9] | Beijing Astronomical Obs., Xinglong, China | 2008 | ||||
| MMT (original optics) | 4.7sigfig=3NaNsigfig=3 (combined)[10] | Multiple Six 1.8sigfig=2NaNsigfig=2 mirrors | F. L. Whipple Obs., Arizona, USA | 1979 Mirrors removed 1998 | |||
| Lowell Discovery Telescope[11] | 4.3sigfig=3NaNsigfig=3 | Single | USA | Lowell Observatory, Happy Jack, Arizona, USA | 2012 | ||
| 4.2sigfig=3NaNsigfig=3 | Single | UK, Netherlands, Spain | Roque de los Muchachos Obs., Canary Islands, Spain | 1987 | |||
| 4.1sigfig=3NaNsigfig=3 | Single | Cerro Pachón (CTIO), Coquimbo Region, Chile | 2002 | ||||
| 4.1sigfig=3NaNsigfig=3 | Single | Paranal Observatory, Antofagasta Region, Chile | 2009 | ||||
| 4sigfig=3NaNsigfig=3 | Single | Cerro Tololo Inter-American Obs., Coquimbo Region, Chile | 1976 | ||||
| 4sigfig=3NaNsigfig=3 | ARIES Devasthal Observatory, Nainital, India | 2022 | |||||
| Nicholas U. Mayall 4 m[12] | 4sigfig=3NaNsigfig=3 | Single | Kitt Peak National Obs., Arizona, USA | 1973 | |||
| 4sigfig=3NaNsigfig=3 | Single | Haleakala Observatory, Hawaii, USA | 2019 | ||||
| Anglo-Australian Telescope (AAT) | 3.89sigfig=3NaNsigfig=3 | Single | Australian Astronomical Obs., New South Wales, Australia | 1974 | |||
| United Kingdom Infrared Telescope (UKIRT) | 3.8sigfig=2NaNsigfig=2 | Single | Mauna Kea Observatories, Hawaii, USA | 1979 | |||
| 3.67 m AEOS Telescope (AEOS) | 3.67sigfig=3NaNsigfig=3 | Single | Air Force Maui Optical Station, Hawaii, USA | 1996 | |||
| 3.6 m Devasthal Optical Telescope[13] (DOT) | 3.6sigfig=3NaNsigfig=3 | Single | India | ARIES Devasthal Observatory, Nainital, India | 2016 | ||
| Telescopio Nazionale Galileo (TNG) | 3.58sigfig=3NaNsigfig=3 | Single | Italy | Roque de los Muchachos Obs., Canary Islands, Spain | 1997 | ||
| New Technology Telescope (NTT) | 3.58sigfig=3NaNsigfig=3 | Single | La Silla Observatory, Coquimbo Region, Chile | 1989 | |||
| Canada-France-Hawaii Telescope (CFHT) | 3.58sigfig=3NaNsigfig=3 | Single | Mauna Kea Observatories, Hawaii, USA | 1979 | |||
| 3.57sigfig=3NaNsigfig=3 | Single | La Silla Observatory, Coquimbo Region, Chile | 1977 | ||||
| MPI-CAHA 3.5 m[14] | 3.5sigfig=3NaNsigfig=3 | Single | West Germany, Spain | Calar Alto Obs., Almería, Spain | 1984 | ||
| USAF Starfire 3.5 m[15] | 3.5sigfig=3NaNsigfig=3 | Single | Starfire Optical Range, New Mexico, USA | 1994 | |||
| 3.5sigfig=3NaNsigfig=3 | Single | Kitt Peak National Obs., Arizona, USA | 1994 | ||||
| 3.5sigfig=3NaNsigfig=3 | 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) | 3.48sigfig=3NaNsigfig=3 | Single | Apache Point Obs., New Mexico, USA | 1994 | |||
| Iranian National Observatory (INO340) | 3.4sigfig=2NaNsigfig=2 | Single | Iran | Mount Gargash, Isfahan Province, Iran | 2022[16] | ||
| 3.05sigfig=3NaNsigfig=3 | Single | Lick Observatory, California, USA | 1959 | ||||
| 3sigfig=3NaNsigfig=3 | Single | Mauna Kea Observatory, Hawaii, USA | 1979 | ||||
| 3sigfig=3NaNsigfig=3 | Liquid | NASA Orbital Debris Obs., New Mexico, USA | 1995 Decommissioned 2002[17] | ||||
| 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.[18] 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.[19] The Keck segments were made by Schott AG. The SALT and LAMOST segments were cast and polished by LZOS.[20] The mirror for Subaru was cast by Corning and polished at Contraves Brashear Systems in Pennsylvania, USA.[21]
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.
These telescopes were the largest in the world at the time of their construction, by the same aperture criterion as above.
| Years Largest | Name | Out | In | Aperture (m) | Area (m2) | M1 Mirror | Note | Altitude (m) | |
|---|---|---|---|---|---|---|---|---|---|
| 2009–Present | 10.4 | 74 | 36 × 1.9 m hexagons M1 mirror | Segmented mirror | 2267 | ||||
| 1993–2009 | 10 | 76 [22] | 36 × 1.8 m hexagons M1 mirror | Segmented mirror, M1 f/1.75 | 4145 | ||||
| 1976–1993 | 6 | 26 | 605 cm f/4 M1 mirror | Mirror replaced twice | 2070 | ||||
| 1948–1976 | 5.1 | - | 508 cm f/3.3 M1 mirror | Art deco dome | 1713 | ||||
| 1917–1948 | 2.54 | - | Also used for 1st optical interferometer | 1742 | |||||
| For earlier entries, see List of largest optical telescopes historically | |||||||||
These telescopes are under construction and will meet the list inclusion criteria once completed:
Selected large telescopes which are in detailed design or pre-construction phases: