This list of the largest optical reflecting telescopes with objective diameters greater than 1.8 meters is sorted by aperture: an optical diameter that reflects light-gathering power of the reflecting telescope's optical assembly and resolution.

The mirrors themselves can be larger than the aperture, and new telescopes can 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 meters) 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 meters) 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 poor measure of a telescope's performance.Space-based telescopes, such as the Hubble Space Telescope, take advantage of being above the Earths atmosphere to reach higher resolution and greater light gathering through longer exposure time.

Table of reflecting telescopes

Multiple mirror telescopes are currently ranked by their equivalent optical area, rather than peak interferometric aperture, unless optical area is irrelevant for the instrument's design.

Name	Image	Effective aperture m	Aper. in	Mirror type	Nationality / Sponsors	Site	Built
Large Binocular Telescope (LBT)		11.8 m (2×8.4 m)	464.6″	Multiple mirror, 2	USA, Italy, Germany	Mount Graham Internationals Obs., Arizona	2004
Gran Telescopio Canarias (GTC)		10.4 m	410″	Segmented, 36	Spain (90%) Mexico, USA	ORM, Canary Islands	2006/9
Keck 1		10 m	400″	Segmented, 36	USA	Mauna Kea Observatory, Hawaii	1993
Keck 2							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 Observatory	2005
Hobby-Eberly Telescope (HET) (11 m × 9.8 m mirror)		9.2 m	362″	Segmented, 91	USA, Germany	McDonald Observatory, Texas	1997
Subaru (JNLT)		8.2 m	323″	Single	Japan	Mauna Kea Observatory, Hawaii	1999
VLT 1 (Antu)		8.2 m	323″	Single	ESO Countries + Chile	Paranal Observatory, Chile	1998
VLT 2 (Kueyen)							1999
VLT 3 (Melipal)							2000
VLT 4 (Yepun)							2001
Gemini North (Gillett)		8.1 m	318″	Single	USA, UK, Canada, Chile, Australia, Argentina, Brazil	Mauna Kea Obs., Hawaii	1999
Gemini South						Cerro Pachón, Chile	2001
MMT	50px]]	6.5 m	256″	Single	USA	F. L. Whipple Obs., Arizona	2000
Magellan 1 (Walter Baade)		6.5 m	256″	Honeycomb	USA	Las Campanas Obs., Chile	2000
Magellan 2 (Landon Clay)							2002
BTA-6		6 m	238″	Single	USSR + Russia	Zelenchukskaya, Caucasus	1975
Large Zenith Telescope (LZT)	50px]]	6 m	236″	Liquid	Canada, France, USA	Maple Ridge, British Columbia	2003
Hale Telescope (200 inch)		5.08 m	200″	Single	USA	Palomar Observatory, California	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–3.6 m	193″	Segmented (37 + 24)	PRC	Beijing Astronomical Obs., Xinglong, China	2008
MMT (6×1.8 m) optics replaced	50px]]	4.5 m (6×1.8 m)	177″	Segmented, 6	USA	F. L. Whipple Obs., Arizona	1979-1998
William Herschel Telescope		4.2 m	165″	Single	UK, Netherlands, Spain	ORM, Canary Islands	1987
SOAR	50px]]	4.1 m	161″	Single	USA, Brazil	Cerro Pachón, Chile	2002
VISTA	50px]]	4.1 m	161″	Single IR	ESO countries	Paranal Obs., Chile	2008
Victor M. Blanco Telescope		4 m	157″	Single	USA	Cerro Tololo Inter-American Obs., Chile	1976
Anglo-Australian Telescope (AAT)		3.89 m	154″	Single	United Kingdom + Australia	Anglo-Australian Obs.; Siding Spring, Australia	1975
Nicholas U. Mayall 4m		3.81 m	158″	Single	USA	Kitt Peak National Obs.; Arizona	1973
United Kingdom Infrared Telescope (UKIRT)		3.8 m	150″	Single IR	United Kingdom	Mauna Kea Observatories; Mauna Kea, Hawaii	1978
3.67m AEOS Telescope (AEOS)	50px]]	3.67 m	145″	Single	USA	Air Force Maui Optical Station; Haleakala, Hawaii	1996
Telescopio Nazionale Galileo(TNG)		3.58 m	138″	Single	Italy	La Palma, Canary Islands	1997
New Technology Telescope (NTT)		3.58 m	142″	Single	ESO countries	European Southern Observatory; Cerro La Silla, Chile	1989
Canada-France-Hawaii Telescope (CFHT)		3.58 m	141″	Single	Canada,France, USA	Mauna Kea Observatories, USA	1979
ESO 3.6 m Telescope		3.57 m	140″	Single	ESO countries	European Southern Observatory; Cerro La Silla, Chile	1977
MPI-CAHA 3.5m	50px]]	3.5 m	138″	Single	West Germany+Spain	Calar Alto Obs., Spain	1984
USAF Starfire 3.5m		3.5 m	138″	Single	USA	Starfire Optical Range; New Mexico	1994
WIYN Telescope	50px]]	3.5 m	138″	Single	USA	Kitt Peak National Obs., USA	1994
Herschel Space Observatory		3.5 m	138″	Single IR	ESA countries	Earth lagrange point L2 (space)	2009
Astrophysical Research Consortium (ARC)	50px]]	3.48 m	137″	Single	USA	Apache Point Obs.; Sacramento Peak, New Mexico	1994
Shane Telescope		3.05 m	120″	Single	USA	Lick Observatory; Mt. Hamilton, California	1959
NASA IRTF		3 m	118″	Single IR	USA	Mauna Kea, Hawaii	1979
NASA-LMT (NODO) retired	50px]]	3 m	118″	Liquid	USA	Sacramento Peak, New Mexico, USA	1995-2002
See 'List of optical telescopes for continuation of list

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 are also known as Mosaic mirrors. Single mirrors, also called monolithic and can be sub-categorized in types, such as solid or honeycomb.

Top telescope 2001-2010

The very largest telescopes are multi-telescope interferometers, and may have longer baselines.However, these astronomical interferometers are less flexible in use.

The largest telescope during the first decade of the 21st century could be either the Gran Telescopio Canarias (one 10.4 diameter mirror), the Large Binocular Telescope (two 8.4 diameter mirrors on a binocular mount), or the Very Large Telescope (with four 8.2 m telescopes, four 1.8 m auxiliary telescopes, and a 2.61 m Survey Telescope). However, as these were still coming online in the period, the two 10 meter Keck Telescopes (with 85 m aperture synthesis) were possibly the largest in full scientific operation.

Name	Out	In	aperture (m)	equiv. Area (m)	Area (m²)	Mirrors	Note	Altitude
Gran Telescopio Canarias (GTC)			10.4	10.4	74 m²	36 x 1.9 m hexagonal segments for M1	Commissioned 2009; Largest single mirror	2267 m
Large Binocular Telescope (LBT)			22.8*	11.7	111 m²	2 x 8.4 m M1 mirrors; 1 mount	Largest Binocular; largest non-segmented mirrors	3190 m
Southern African Large Telescope (SALT)		50px	11	9.2	66-45 m²	92 x 1 m hexagon; 11 x 9.8 m mirror	Spherical M1 w/ fixed mirror; spectroscopy (see HET or here)	1783 m
Keck 1 & 2			10 m each	10 m	76 m2 each	36 x 1.8 m hexagons M1 mirrors each	largest twin telescopes	4145 m

*The LBT telescope baseline is via aperture synthesis. Largest telescopes with interferometer mode: {| class="wikitable sortable" style="font-size:95%;" |- ! Name || Longest baseline (m) || Mirrors || Area || Equiv. || Note |- | [[VLTI]] || 200 || 4 x 8.2 m (VLT 1,2,3, & 4) || 210 m² http://science.jrank.org/pages/6736/Telescope-Modern-optical-telescopes.html || 16 || Behind schedule |- |[[Keck Interferometer]] || 85 || 2 x 10 m (Keck 1 & 2) || 152 m² |- | LBT || 22.8* || 2 x 8.4 || 110 m² || 11.7 || One telescope mount* |- |[[Navy Prototype Optical Interferometer]] || 437 || 6 siderostats (visible) || Sparse Aperture |- |} *Baseline does not reduce with viewing angle

Under construction or planned

Below are listed telescopes that are still in the conceptual/proposed stage or still under construction.

Under construction

• European Extremely Large Telescope 42 m (140 ft)
• Thirty Meter Telescope 30 m
• Giant Magellan Telescope 7×8.4 m mirrors = 24.5 m aperture (21.4 m equivalent area)
• Large Synoptic Survey Telescope 8.4 m
• James Webb Space Telescope 6.5 m
• Discovery Channel Telescope 4.2 m (13.8 ft)
• Automated Planet Finder 2.4 m
• Pan-STARRS 4 x 1.8 m (1 online)
• Magdalena Ridge Observatory Telescope Array 10 x 1.4 m
• Thai National Telescope Project 2.4 m
• Advanced Technology Solar Telescope 4 m
• International Liquid Mirror Telescope 4 m

Proposed or Planned

• Overwhelmingly Large Telescope 100 m study concluded
• Euro 50 50 m study concluded
• Large Atacama Telescope
• Hubble Origins Probe study concluded
• ALPACA telescope, 8 m liquid mirror
• Advanced Technology Large-Aperture Space Telescope (ATLAS), 8-15m space telescope

See also

• Extremely large telescope
• List of largest optical refracting telescopes
• List of optical telescopes
• List of largest optical telescopes historically
• List of astronomical interferometers at visible and infrared wavelengths
• List of largest optical telescopes in the 20th century

References

1. The Telescope, By Geoff Andersen, Page 165
3. http://spacecraftkits.com/KFacts.html
4. Thai National Telescope Project

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
• Stellafane telescope links
• google units calculator