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) 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 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.

Reflecting Telescopes

Name	Image	Effective aperture m	Aper. in	Mirror type	Nationality / Sponsors	Site	Built
Gran Telescopio Canarias (GTC)		10.4 m	409″	Segmented, 36	Spain (90%), Mexico, USA	Roque de los Muchachos Obs., Canary Islands, Spain	2006/9
Keck 1		10 m	394″	Segmented, 36	USA	Mauna Kea Observatories, Hawaii, USA	1993
Keck 2		10 m	394″	Segmented, 36	USA	Mauna Kea Observatories, Hawaii, USA	1996
Southern African Large Telescope (SALT) 11 m × 9.8 m mirror		9.2 m	362″	Segmented, 91	South Africa, USA, UK, Germany, Poland, New Zealand	South African Astronomical Obs., Northern Cape, South Africa	2005
Hobby-Eberly Telescope (HET) 11 m × 9.8 m mirror		9.2 m	362″	Segmented, 91	USA, Germany	McDonald Observatory, Texas, USA	1997
Large Binocular Telescope (LBT) Phased-array optics for combined 11.9 m		8.4 m × 2	330″ × 2	Multiple mirror, 2	USA, Italy, Germany	Mount Graham International Observatory, Arizona, USA	2004
Subaru (JNLT)		8.2 m	323″	Single	Japan	Mauna Kea Observatories, Hawaii, USA	1999
VLT UT1 – Antu		8.2 m	323″	Single	ESO Countries, Chile	Paranal Observatory, Antofagasta Region, Chile	1998
VLT UT2 – Kueyen		8.2 m	323″	Single	ESO Countries, Chile	Paranal Observatory, Antofagasta Region, Chile	1999
VLT UT3 – Melipal		8.2 m	323″	Single	ESO Countries, Chile	Paranal Observatory, Antofagasta Region, Chile	2000
VLT UT4 – Yepun		8.2 m	323″	Single	ESO Countries, Chile	Paranal Observatory, Antofagasta Region, Chile	2001
Gemini North (Gillett)		8.1 m	318″	Single	USA, UK, Canada, Chile, Australia, Argentina, Brazil	Mauna Kea Observatories, Hawaii, USA	1999
Gemini South		8.1 m	318″	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″	Single	USA	F. L. Whipple Obs., Arizona, USA	2000
Magellan 1 (Walter Baade)		6.5 m	256″	Honeycomb	USA	Las Campanas Obs., Coquimbo Region, Chile	2000
Magellan 2 (Landon Clay)		6.5 m	256″	Honeycomb	USA	Las Campanas Obs., Coquimbo Region, Chile	2002
BTA-6		6 m	238″	Single	USSR/Russia	Special Astrophysical Obs., Karachay–Cherkessia, Russia	1975
Large Zenith Telescope (LZT)		6 m	236″	Liquid	Canada, France, USA	Maple Ridge, British Columbia, Canada	2003
Hale Telescope (200 inch)		5.08 m	200″	Single	USA	Palomar Observatory, California, USA	1948
LAMOST 7000490000000000000♠ (6.67 m × 6.05 m + 5.72 m × 4.40 m corrector; effective aperture 3.6–4.9 m)		4.9 m–3.6 m	193″	Segmented (37 + 24)	PRC (China)	Beijing Astronomical Obs., Xinglong, China	2008
MMT (original optics: 6 × 1.8 m) →see above record for current 6.5 m mirror		4.7 m (6×1.8 m)	186″	Segmented, 6	USA	F. L. Whipple Obs., Arizona, USA	1979–1998
Discovery Channel Telescope		4.3 m	169″	Single	USA	Lowell Observatory, Happy Jack, Arizona, USA	2012
William Herschel Telescope		4.2 m	165″	Single	UK, Netherlands, Spain	Roque de los Muchachos Obs., Canary Islands, Spain	1987
SOAR		4.1 m	161″	Single	USA, Brazil	Cerro Pachón (CTIO), Coquimbo Region, Chile	2002
VISTA		4.1 m	161″	Single	ESO Countries, Chile	Paranal Observatory, Antofagasta Region, Chile	2009
Victor M. Blanco Telescope		4 m	157″	Single	USA	Cerro Tololo Inter-American Obs., Coquimbo Region, Chile	1976
Nicholas U. Mayall 4 m		4 m	149.5″	Single	USA	Kitt Peak National Obs., Arizona, USA	1973
Anglo-Australian Telescope (AAT)		3.89 m	154″	Single	Australia, UK	Australian Astronomical Obs., New South Wales, Australia	1975
3.67 m AEOS Telescope (AEOS)		3.67 m	145″	Single	USA	Air Force Maui Optical Station, Hawaii, USA	1996
Telescopio Nazionale Galileo (TNG)		3.58 m	138″	Single	Italy	Roque de los Muchachos Obs., Canary Islands, Spain	1997
New Technology Telescope (NTT)		3.58 m	142″	Single	ESO countries	La Silla Observatory, Coquimbo Region, Chile	1989
Canada-France-Hawaii Telescope (CFHT)	Error creating thumbnail: File missing	3.58 m	141″	Single	Canada, France, USA	Mauna Kea Observatories, Hawaii, USA	1979
ESO 3.6 m Telescope		3.57 m	140″	Single	ESO countries	La Silla Observatory, Coquimbo Region, Chile	1977
MPI-CAHA 3.5 m		3.5 m	138″	Single	West Germany, Spain	Calar Alto Obs., Almería, Spain	1984
USAF Starfire 3.5 m		3.5 m	138″	Single	USA	Starfire Optical Range, New Mexico, USA	1994
WIYN Telescope		3.5 m	138″	Single	USA	Kitt Peak National Obs., Arizona, USA	1994
Space Surveillance Telescope		3.5 m	138″	Single	USA	White Sands Missile Range, New Mexico, USA	2011
Astrophysical Research Consortium (ARC)		3.48 m	137″	Single	USA	Apache Point Obs., New Mexico, USA	1994
Shane Telescope		3.05 m	120″	Single	USA	Lick Observatory, California, USA	1959
NASA Infrared Telescope Facility		3.0 m	120″	Single	USA	Mauna Kea Observatory, Hawaii, USA	1979
NASA-LMT →retired, private		3 m	118″	Liquid	USA	NASA Orbital Debris Obs., New Mexico, USA	1995–2002
See List of large optical reflecting telescopes for continuation of list

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.

Comparison of nominal sizes of primary mirrors of some notable optical telescopes (click for detail)

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.

Top telescopes of 2010

The largest telescopes are multi-telescope interferometers, and may have longer baselines. However, these astronomical interferometers are less flexible in use, and many interferometers cannot form images or see faint objects despite their high peak angular resolution.

The largest telescope during the first decade of the 21st century could be either the Gran Telescopio Canarias (one 10.4 m diameter mirror), the Large Binocular Telescope (two 8.4 m diameter mirrors on a binocular mount), or the Very Large Telescope (with four 8.2 m telescopes and four 1.8 m auxiliary telescopes). However, as these were still coming online in the period, the two 10 m Keck Telescopes (with 85 m aperture synthesis) were possibly the largest in full scientific operation.

Note other wavelengths of telescopes can be much larger physically, such as the 305 m aperture Arecibo radio telescope, but since radio wavelengths are also larger, this does not necessarily translate into brighter or higher resolution images.

Reflecting Telescopes (2010)

Name	Out	In	Aperture (m)	Equiv. Area (m)	Area (m2)	Mirrors	Note	Altitude (m)
Gran Telescopio Canarias (GTC)			10.4	10.4	74	36 × 1.9 m hexagonal segments for M1	Commissioned 2009; Largest single mirror	2267
Southern African Large Telescope (SALT)			11 (max.)	9.2	66–45	92 × 1 m hexagon; 11 × 9.8 m mirror	HET twin but larger optically. Spherical M1 w/ fixed mirror; spectroscopy (see here [2])	1783
Keck 1 & 2			10 m each	10	76 (each)	36 × 1.8 m hexagons M1 mirrors each	largest twin telescopes 152 m2 total optical area	4145
VLT 1, 2, 3 & 4			8.2 (each)	8.2	53 (each)	1 x 8.2 m M1 each	Largest quadruplet telescope 210 (total optical area)	2635
Large Binocular Telescope (LBT)			8.4 m each	11.7	111 (both sides)	2 x 8.4 m M1 mirrors; 1 mount	Largest Binocular; largest non-segmented mirrors; 22.8 m aperture planned	3221

Largest telescopes with interferometer mode, and two image-forming interferometer arrays.

Reflecting Telescopes (with Interferometer mode)

Name	Longest baseline (m)	Mirrors	Area (m2)	Equiv.	Note
VLTI	200	4 × 8.2 m (VLT 1,2,3, & 4)	210	16	Behind schedule in 2010, 4 units at 130 m success in 2012
Keck Interferometer	85	2 × 10 m (Keck 1 & 2)	152		Operations ceased in 2012.
Large Binocular Telescope (LBTI)	22.8*	2 × 8.4 m	110	11.9	One telescope mount*; Fizeau & Amplitude Interferometry
CHARA array	330	6 × 1 m	2.45
NPOI	437	6 siderostats (visible)	Sparse Aperture		Optically resolved Mizar (star)

*Baseline does not reduce with viewing angle

Top telescopes of 2000

Reflecting Telescopes (2000)

Name	Out	In	Aperture (m)	Area (m2)	Mirrors	Note	Altitude (m)
Keck 1 & 2			10 (each)	76 (each)	36 × 1.8 m hexagons M1 mirrors each	largest twin telescopes, largest aperture mirrors, 152 m2 total optical area	4145
Hobby-Eberly Telescope (HET)			9.2 (max.)	66–45	92 x 1 m hexagon; 11 × 9.8 m mirror	Spherical M1 w/ fixed mirror; spectroscopy	2030
Subaru Telescope			8.2	53	1 × 8.3 m M1	Largest single piece mirror (tied with the 4 VLT)	4145
UT1 – Antu			8.2	53	1 x 8.2 m M1	Part of a quadruplet telescope setup	2635
UT2 – Kueyen			8.2	53	1 x 8.2 m M1	Part of a quadruplet telescope setup	2635
UT3 – Melipal			8.2	53	1 x 8.2 m M1	Part of a quadruplet telescope setup	2635

Under construction

Reflecting Telescopes (2000)

Name	Out	In	Aperture (m)	Area (m2)	Mirrors	Note	Altitude (m)
VLT 1, 2, 3			8.2 (each)	53 (each)	1 x 8.2 m M1	By the year 2000 three unit telescopes were online; each were the largest single piece mirrors at that time (tied with Subaru)	2635

Chronologically

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	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

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

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 (first light planned for 2022)
• Giant Magellan Telescope 7 × 8.4 m mirrors (24.5 m aperture; 21.4 m equivalent area)
• Large Synoptic Survey Telescope 8.4 m (development approved as of 2012 for 2021 first light)
• James Webb Space Telescope 6.5 m (2018 launch planned)
• Pan-STARRS 4 × 1.8 m (1 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)
• 3.6 m Devasthal Optical Telescope (Indo-Belgian telescope)
• San Pedro Martir Telescope 6.5 m (completion expected for Summer 2018)

Proposed

• Advanced Technology Large-Aperture Space Telescope (ATLAST), 8–15 m space telescope
• Chinese Giant Solar Telescope (CGST). China aims to build a very large infrared and optical solar telescope, with the spatial resolution expected to be equivalent to an 8-meter-diameter telescope and light-gathering power equivalent to a 5 m diameter full aperture telescope
• High-Definition Space Telescope - proposed segmented mirror telescope 39 feet (12 meters) in aperture, placed at the L2 lagrange point

See also

• 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

Further reading

• "The Astronomical Scrapbook", Joseph Ashbrook, Sky Publishing Corporation 1984, ISBN 0-933346-24-7, o
• "Giant Telescopes of the World", Sky and Telescope, August 2000.
• "The History of the Telescope", Henry C. King. (1955)
• "The Historical Growth of Telescope Aperture", René Racine, Publications of the Astronomical Society of the Pacific, 116
• JRASC (1929) vol 23, p351
• Sky&Telescope (April 1981) p303
• Sky&Telescope (July 1993) vol 86, p 27-32
• James H. Burge, 1993 Dissertation at UA, "Advanced Techniques for Measuring Primary Mirrors for Astronomical Telescopes"

External links

• List of large reflecting telescopes
• The World's Largest Optical Telescopes
• Largest optical telescopes of the world
• Selected largest telescopes