List of largest optical reflecting telescopes

The world's largest optical reflecting telescopes with an aperture diameter of larger than 8 metres (hover with mouse over image). Legend: GTC · Keck · Subaru HET · LBT · VLT SALT · Gemini (N) · Gemini (S)

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.^[1] 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	Image	Effective aperture	Mirror type	Nationality / Sponsors	Site	First light
Large Binocular Telescope (LBT)		11.9 m (469 in) (combined)[2]	Multiple Two 8.4 m (331 in) mirrors	USA, Italy, Germany	Mount Graham International Observatory, Arizona, USA	2004
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) [3]	Segmented 91 × 1 m (39 in) hexagonal segments forming a 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)[4]	Segmented 91 × 1 m (39 in) hexagonal segments forming a 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
MMT (current optics)		6.5 m (256 in)	Single	USA	F. L. Whipple Obs., Arizona, USA	2000
Magellan 1 (Walter Baade)[5]		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
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 [6]	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)[7]	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[8]	China	Beijing Astronomical Obs., Xinglong, China	2008
MMT (original optics) (see above for current version)		4.7 m (185 in) (combined)[9]	Multiple Six 1.8 m (71 in) mirrors	USA	F. L. Whipple Obs., Arizona, USA	1979 Mirrors removed 1998
Lowell Discovery Telescope[10]		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[11]		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[12] (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[13]		3.5 m (138 in)	Single	West Germany, Spain	Calar Alto Obs., Almería, Spain	1984
USAF Starfire 3.5 m[14]		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
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[15]
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.^[16] 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.^[17] The Keck segments were made by Schott AG. The SALT and LAMOST segments were cast and polished by LZOS.^[18] The mirror for Subaru was cast by Corning and polished at Contraves Brashear Systems in Pennsylvania.^[19]

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.

Comparison of nominal sizes of apertures of some notable optical telescopes

For the largest reflecting telescopes on the planet, the horizontal indicates the year built and the vertical direction indicates the size of the mirror measured in meters. Countries which contain several of these telescopes are color-coded for identification.

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 [20]	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[]

Sketch of the Messier 51 by William Parsons in 1845, later known as the Whirlpool Galaxy

Whirlpool Galaxy (M51A/B or NGC 5194/5) by NASA/ESA from Hubble Space Telescope in 2005

Under construction[]

These telescopes are currently under construction and will meet the list inclusion criteria once completed:

• European Extremely Large Telescope 39.3 m (1,550 in). First light planned in 2024.^[21]
• Thirty Meter Telescope 30 m (1,200 in). First light planned in 2027.^[22]
• Giant Magellan Telescope. Seven 8.4 m mirrors on a single mount, giving the resolving power of a single 24.5 m mirror and the light gathering area of a single 21.4 m mirror. First light planned in 2029.^[23]
• Vera C. Rubin Observatory 8.4 m (330 in). First light planned in 2021 and full operations beginning in 2022.
• James Webb Space Telescope 6.5 m (260 in). Infrared space telescope, launch expected in November or December 2021,^[24] with operations beginning 6 months later.
• San Pedro Martir Telescope 6.5 m (260 in). First light planned in 2023.^[25]
• Magdalena Ridge Observatory Telescope Array. Optical interferometer array, 10 telescopes each of 1.4 m (55 in) aperture; equivalent to a 4.4 m (170 in) single aperture.
• 4 m (160 in). Construction began in 2013.^{[26][failed verification][needs update]}
• 3.8 m (150 in). First light planned in 2021.^[27][28]
• Iranian National Observatory 3.4 m (130 in). First light planned in 2021.^[29]

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.
• Tokyo Atacama Observatory (TAO) 6.5 m (260 in)^[30]
• Chinese Giant Solar Telescope (CGST), an infrared and optical solar telescope, with light-gathering power equivalent to a 5 m diameter aperture ^[31][32]

See also[]

• List of telescope types
• Lists of telescopes

References[]

Further reading[]

• Racine, René (2004). "The Historical Growth of Telescope Aperture". Publications of the Astronomical Society of the Pacific. 116 (815): 77. Bibcode:2004PASP..116...77R. doi:10.1086/380955.

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)