List of largest optical reflecting telescopes


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.

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)

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 telescopesEdit

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 an 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 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)   8.2 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
James Webb Space Telescope   6.5 m

(256 in)

18 hexagonal segments
NASA, ESA, CSA Halo orbit around the Earth-Sun L2 Point 2022
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
Víctor M. Blanco Telescope   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]   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.
Astrophysical Research Consortium (ARC)   3.48 m (137 in) Single USA Apache Point Obs., New Mexico, USA 1994
Iranian National Observatory (INO340)
3.4 m (130 in) Single Iran Mount Gargash, Isfahan Province, Iran 2022[15]
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[16]
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.[17] 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.[18] The Keck segments were made by Schott AG. The SALT and LAMOST segments were cast and polished by LZOS.[19] The mirror for Subaru was cast by Corning and polished at Contraves Brashear Systems in Pennsylvania.[20]

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 telescopesEdit

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 [21] 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 telescopesEdit

Under constructionEdit

The Extremely Large Telescope under construction in January 2022

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

  • Extremely Large Telescope, Chile — 39.3 m (1,550 in). First light planned in 2027.[22]
  • Thirty Meter Telescope, Hawaii, USA — 30 m (1,200 in). Construction began in 2014 but halted in 2015; as of 2022 it has not resumed.[23]
  • Giant Magellan Telescope, Chile — seven 8.4 m mirrors on a single mount. This provides an effective aperture equivalent to a 21.4 m mirror and the resolving power equivalent to a 24.5 m mirror. First light planned in 2029.[24]
  • Vera C. Rubin Observatory, Chile — 8.4 m (330 in). First light planned in 2024.[25]
  • San Pedro Martir Telescope, Baja California, Mexico — 6.5 m (260 in). First light planned in 2023.[26]
  • Magdalena Ridge Observatory Interferometer, New Mexico, USA — An optical interferometer array with ten 1.4 m (55 in) telescopes. The light gathering power is equivalent to a 4.4 m (170 in) single aperture. The first telescope was installed in 2016; construction was paused in 2019 due to insufficient funding[27] and has not resumed.
  • Timau National Observatory, Indonesia — 3.8 m (150 in). First light planned in 2021.[28][29][needs update]


Scale comparison between the primary mirrors of the Hubble Space Telescope, James Webb Space Telescope, and the proposed LUVOIR-B and LUVOIR-A.

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

See alsoEdit


  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). Stepp, Larry M; Gilmozzi, Roberto; Hall, Helen J (eds.). "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. S2CID 119272065.
  13. ^ "Max-Planck-Institut für Astronomie". July 20, 1994. Retrieved August 19, 2009.
  14. ^ John Pike. "Starfire". Retrieved August 19, 2009.
  15. ^ Stone, Richard (19 October 2022). "'The door is open': Iranian astronomers seek collaborations for their new, world-class telescope". Science. doi:10.1126/science.adf4145. Retrieved 21 October 2022.
  16. ^ "NASA Orbital Debris Observatory". Retrieved August 19, 2009.
  17. ^ "Polissage Optique pour les Grands Instruments de la Physique et de l 'Astronomie" (PDF). Archived from the original (PDF) on 2012-04-26.
  18. ^ "Mirror Castings". Steward Observatory Mirror Lab.
  19. ^ "Large Optics Manufacturing in Large Optics Manufacturing in Lytkarino Optical Glass Factory, Russia" (PDF). Archived from the original (PDF) on 2012-04-26.
  20. ^ "SUBARU Telescope 8.3m Primary Mirror Finished".
  21. ^ "Keck Telescope Facts". Retrieved 2012-01-03.
  22. ^ "Groundbreaking for the E-ELT (eso1419 — Organisation Release)". ESO. 19 June 2014. Retrieved 3 January 2015.
  23. ^ "Timeline". TMT International Observatory. Retrieved 27 September 2022.
  24. ^ "Quick Facts". Retrieved 2021-02-15.
  25. ^ "Construction Project Status". Rubin Observatory. 16 October 2022. Retrieved 17 October 2022. 14-Mar-2024 System First Light
  26. ^ Universities in U.S. and Mexico Partner on Telescope Project. Arizona Public Media, 13 November 2017.
  27. ^ 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.
  28. ^ Irawan, Gita (2019-11-26). "Menristek Sebut Observatorium Nasional Timau NTT Ditargetkan Selesai Tahun Depan". tribunnews (in Indonesian). Retrieved 2020-05-19.
  29. ^ "A New Era of Indonesian Space, Largest Observatory in Southeast Asia Founded". Retrieved February 15, 2021.
  30. ^ 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). Hall, Helen J; Gilmozzi, Roberto; Marshall, Heather K (eds.). "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. S2CID 124828278.
  31. ^ "Introduction to the Chinese Giant Solar Telescope" (PDF).
  32. ^ Staff (29 August 2012). "China Exclusive: Scientists looking for site for giant solar telescope". Retrieved 8 December 2014.
  33. ^ Shiga, David (2 June 2008). "Liquid-mirror telescopes are a reality at last". New Scientist. Retrieved 18 June 2022.
  34. ^ "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 readingEdit

  • 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 linksEdit

  • 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)