List of largest optical reflecting telescopes

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The world's largest optical reflecting telescopes with an aperture diameter of larger than 8 metres (hover with mouse over image).

GTC · Keck · Subaru
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[edit]

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) LBT-Gebaeude.jpg 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) Grantelescopio.jpg 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) HET Dome.jpg 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 KeckTelescopes-hi.png 10 m (394 in) Segmented
36 hexagonal segments
USA Mauna Kea Observatories, Hawaii, USA 1993
Keck 2 KeckTelescopes-hi.png 10 m (394 in) Segmented
36 hexagonal segments
USA Mauna Kea Observatories, Hawaii, USA 1996
Southern African Large Telescope (SALT) Southern African Large Telescope 720x576px.jpg 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) MaunaKea Subaru.jpg 8.2 m (323 in) Single Japan Mauna Kea Observatories, Hawaii, USA 1999
VLT UT1 – Antu Paranal opendome.jpg 8.2 m (323 in) Single ESO Countries, Chile Paranal Observatory, Antofagasta Region, Chile 1998
VLT UT2 – Kueyen UVES on UT2-KUEYEN.jpg 8.2 m (323 in) Single ESO Countries, Chile Paranal Observatory, Antofagasta Region, Chile 1999
VLT UT3 – Melipal Paranal UT3 2008-01-04.jpg 8.2 m (323 in) Single ESO Countries, Chile Paranal Observatory, Antofagasta Region, Chile 2000
VLT UT4 – Yepun Cloaked in Stars.jpg 8.2 m (323 in) Single ESO Countries, Chile Paranal Observatory, Antofagasta Region, Chile 2001
Gemini North (Gillett) Gemini Observatory at sunset.jpg 8.1 m (319 in) Single USA, UK, Canada, Chile, Australia, Argentina, Brazil Mauna Kea Observatories, Hawaii, USA 1999
Gemini South Gemini South 01.jpg 8.1 m (319 in) Single USA, UK, Canada, Chile, Australia, Argentina, Brazil Cerro Pachón (CTIO), Coquimbo Region, Chile 2001
James Webb Space Telescope JWST spacecraft model 3.png 6.5 m

(256 in)

18 hexagonal segments
NASA, ESA, CSA Halo orbit around the Earth-Sun L2 Point 2022
MMT (current optics) MMT Observatory.jpg 6.5 m (256 in) Single USA F. L. Whipple Obs., Arizona, USA 2000
Magellan 1 (Walter Baade)[5] Magellan telescopes.jpg 6.5 m (256 in) Single USA Las Campanas Obs., Atacama Region, Chile 2000
Magellan 2 (Landon Clay) Magellan telescopes.jpg 6.5 m (256 in) Single USA Las Campanas Obs., Atacama Region, Chile 2002
BTA-6 Главная обсерватория.jpg 6 m (236 in) Single USSR/Russia Special Astrophysical Obs., Karachay–Cherkessia, Russia 1975
Large Zenith Telescope (LZT) 180724main 6-mMirror.jpg 6 m (236 in) Liquid Canada, France, United States [6] Maple Ridge, British Columbia, Canada 2003
Decommissioned 2016
Hale Telescope P200 Dome Open.jpg 5.08 m (200 in) Single USA Palomar Observatory, California, USA 1949
LAMOST LAMOST telescope org.jpg 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)
MMT Observatory.jpg 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] The Dome of Discovery Channel Telecope.JPG 4.3 m (169 in) Single USA Lowell Observatory, Happy Jack, Arizona, USA 2012
William Herschel Telescope William herschel Telescope Dome.jpg 4.2 m (165 in) Single UK, Netherlands, Spain Roque de los Muchachos Obs., Canary Islands, Spain 1987
SOAR SOAR telescope at twlight.jpg 4.1 m (161 in) Single USA, Brazil Cerro Pachón (CTIO), Coquimbo Region, Chile 2002
VISTA VISTA at Paranal Eso0704b.tif 4.1 m (161 in) Single ESO Countries, Chile Paranal Observatory, Antofagasta Region, Chile 2009
Victor M. Blanco Telescope 4m-Victor M. Blanco Telescope.jpg 4 m (157 in) Single USA Cerro Tololo Inter-American Obs., Coquimbo Region, Chile 1976
International Liquid Mirror Telescope 4 m (157 in) Liquid Belgium, Canada, India, Poland ARIES Devasthal Observatory, Nainital, India 2022
Nicholas U. Mayall 4 m[11] Kittpeakteliscope.JPG 4 m (157 in) Single USA Kitt Peak National Obs., Arizona, USA 1973
Daniel K. Inouye Solar Telescope Haleakala Observatory 2017.jpg 4 m (157 in) Single USA Haleakala Observatory, Hawaii, USA 2019.
Anglo-Australian Telescope (AAT) Anglo-Australian Telescope dome.JPG 3.89 m (153 in) Single Australia, UK Australian Astronomical Obs., New South Wales, Australia 1974
United Kingdom Infrared Telescope (UKIRT) UKIRT at sunset (straightened).jpg 3.8 m (150 in) Single UK, United States Mauna Kea Observatories, Hawaii, USA 1979
3.67 m AEOS Telescope (AEOS) AEOS3 lg.jpg 3.67 m (144 in) Single USA Air Force Maui Optical Station, Hawaii, USA 1996
3.6 m Devasthal Optical Telescope[12] (DOT) 3.6m Devasthal Optical Telescope.jpg 3.6 m (142 in) Single India ARIES Devasthal Observatory, Nainital, India 2016
Telescopio Nazionale Galileo (TNG) Tng 2001.jpg 3.58 m (141 in) Single Italy Roque de los Muchachos Obs., Canary Islands, Spain 1997
New Technology Telescope (NTT) La Silla NTT.jpg 3.58 m (141 in) Single ESO countries La Silla Observatory, Coquimbo Region, Chile 1989
Canada-France-Hawaii Telescope (CFHT) Canada-France-Hawaii-Telescope-dome.jpeg 3.58 m (141 in) Single Canada, France, USA Mauna Kea Observatories, Hawaii, USA 1979
ESO 3.6 m Telescope Wallpaper of 3.6-m Telescope at La Silla.jpg 3.57 m (141 in) Single ESO countries La Silla Observatory, Coquimbo Region, Chile 1977
MPI-CAHA 3.5 m[13] Bacares09.jpg 3.5 m (138 in) Single West Germany, Spain Calar Alto Obs., Almería, Spain 1984
USAF Starfire 3.5 m[14] Big3 5mtele.png 3.5 m (138 in) Single USA Starfire Optical Range, New Mexico, USA 1994
WIYN Telescope WIYN OBSERVATORY ON KITT PEAK.jpg 3.5 m (138 in) Single USA Kitt Peak National Obs., Arizona, USA 1994
Space Surveillance Telescope Space Surveillance Telescope.jpg 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.
Astrophysical Research Consortium (ARC) D70050914 15 ApolloLLR.jpg 3.48 m (137 in) Single USA Apache Point Obs., New Mexico, USA 1994
Shane Telescope Shane dome.JPG 3.05 m (120 in) Single USA Lick Observatory, California, USA 1959
NASA Infrared Telescope Facility Afshin Darian - NASA Infrared Telescope Facility.jpg 3.0 m (118 in) Single USA Mauna Kea Observatory, Hawaii, USA 1979
NASA-LMT Liquid Mirror Telescope.jpg 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[edit]

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 Grantelescopio.jpg Gran Telescopio Canarias.jpg 10.4 74 36 × 1.9 m hexagons M1 mirror Segmented mirror 2267
1993–2009 Keck 1 KeckTwilight-hi.png KeckObservatory20071013.jpg 10 76 [20] 36 × 1.8 m hexagons M1 mirror Segmented mirror, M1 f/1.75 4145
1976–1993 BTA-6 Главная обсерватория.jpg SAO-6m-Telescope-main-mirror.jpg 6 26 605 cm f/4 M1 mirror Mirror replaced twice 2070
1948–1976 Hale (200 inch) P200 Dome Open.jpg Palomar arp 600pix.jpg 5.1 508 cm f/3.3 M1 mirror Art deco dome 1713
1917–1948 Hooker (100 inch) 100inchHooker.jpg 2.54 Also used for 1st optical interferometer 1742
For earlier entries, see List of largest optical telescopes historically

Future telescopes[edit]

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[edit]

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


Selected large telescopes which are in detailed design or pre-construction phases:

See also[edit]


  1. ^ "Neptune from the VLT and Hubble". Retrieved 2021-02-23.
  2. ^ SPIE 2006 in Orlando - Proceedings of SPIE conference 6267 on "Ground-based and Airborne Telescopes", "The Large Binocular Telescope", John M. Hill, Richard F. Green and James H. Slagle
  3. ^ "Upgraded Hobby-Eberly Telescope Sees First Light". McDonald Observatory. Retrieved 2016-07-29.
  4. ^ "Howstuffworks "10 Amazing Telescopes"". Archived from the original on December 22, 2008. Retrieved August 19, 2009.
  5. ^ "The Carnegie Observatories – Magellan Telescopes". Carnegie Institution for Science. Retrieved 2017-05-24.
  6. ^ The Telescope, By Geoff Andersen, Page 165
  7. ^ [1] Archived July 22, 2011, at the Wayback Machine
  8. ^ "LAMOST Homepage – Gallery". August 13, 2012. Retrieved January 6, 2018.
  9. ^ Dwayne DayMonday, May 11, 2009 (2009-05-11). "Mirrors in the dark". The Space Review. Retrieved 2012-01-03.{{cite web}}: CS1 maint: multiple names: authors list (link)
  10. ^ Lowell Observatory - 4.3-meter DCT
  11. ^ "The Mayall 4-Meter Telescope". February 27, 1973. Retrieved August 19, 2009.
  12. ^ Sagar, Ram; Brijesh Kumar; Amitesh Omar; A. K. Pandey (2012). "New optical telescope projects at Devasthal Observatory". Proceedings of the Society of Photo-Optical Instrumentation Engineers. Ground-based and Airborne Telescopes IV. 8444: 84441T. arXiv:1304.2474. Bibcode:2012SPIE.8444E..1TS. doi:10.1117/12.925634.
  13. ^ "Max-Planck-Institut für Astronomie". July 20, 1994. Retrieved August 19, 2009.
  14. ^ John Pike. "Starfire". Retrieved August 19, 2009.
  15. ^ "NASA Orbital Debris Observatory". Retrieved August 19, 2009.
  16. ^ "Polissage Optique pour les Grands Instruments de la Physique et de l 'Astronomie" (PDF). Archived from the original (PDF) on 2012-04-26.
  17. ^ "Mirror Castings". Steward Observatory Mirror Lab.
  18. ^ "Large Optics Manufacturing in Large Optics Manufacturing in Lytkarino Optical Glass Factory, Russia" (PDF). Archived from the original (PDF) on 2012-04-26.
  19. ^ "SUBARU Telescope 8.3m Primary Mirror Finished".
  20. ^ "Keck Telescope Facts". Retrieved 2012-01-03.
  21. ^ "Groundbreaking for the E-ELT (eso1419 — Organisation Release)". ESO. 19 June 2014. Retrieved 3 January 2015.
  22. ^ TMT Timeline, accessed June 22, 2019
  23. ^ "Quick Facts". Retrieved 2021-02-15.
  24. ^ Universities in U.S. and Mexico Partner on Telescope Project. Arizona Public Media, 13 November 2017.
  25. ^ Creech-Eakman, Michelle J.; Romero, V. D.; Haniff, Christopher A.; et al. (13 December 2020). Setting the stage for first fringes with the Magdalena Ridge Observatory Interferometer. Optical and Infrared Interferometry and Imaging VII. Proceedings of the SPIE. Vol. 11446. p. 1144609. Bibcode:2020SPIE11446E..09C. doi:10.1117/12.2563173.
  26. ^ Irawan, Gita (2019-11-26). "Menristek Sebut Observatorium Nasional Timau NTT Ditargetkan Selesai Tahun Depan". tribunnews (in Indonesian). Retrieved 2020-05-19.
  27. ^ "A New Era of Indonesian Space, Largest Observatory in Southeast Asia Founded". Retrieved February 15, 2021.
  28. ^ "National observatory to come on stream by mid-June 2021". October 28, 2020. Retrieved February 15, 2021.
  29. ^ Yoshii, Y.; Doi, M.; Kohno, K.; Miyata, T.; Motohara, K.; Kawara, K.; Tanaka, M.; Minezaki, T.; Sako, S.; Morokuma, T.; Tamura, Y.; Tanabe, T.; Takahashi, H.; Konishi, M.; Kamizuka, T.; Kato, N.; Aoki, T.; Soyano, T.; Tarusawa, K.; Handa, T.; Koshida, S.; Bronfman, L.; Ruiz, M. T.; Hamuy, M.; Garay, G. (2016). "The University of Tokyo Atacama Observatory 6.5m telescope: Project overview and current status". Ground-Based and Airborne Telescopes VI. 9906: 99060R. Bibcode:2016SPIE.9906E..0RY. doi:10.1117/12.2231391. hdl:10150/632264.
  30. ^ "Introduction to the Chinese Giant Solar Telescope" (PDF).
  31. ^ Staff (29 August 2012). "China Exclusive: Scientists looking for site for giant solar telescope". Retrieved 8 December 2014.
  32. ^ Shiga, David (2 June 2008). "Liquid-mirror telescopes are a reality at last". New Scientist. Retrieved 18 June 2022.
  33. ^ "Advanced Liquid-mirror Probe of Astrophysics, Cosmology and Asteroids)". Liquid-Mirror Telescope. Astronomy and Astrophysics at the University of British Columbia. Retrieved 18 June 2022.

Further reading[edit]

External links[edit]