List of largest optical reflecting telescopes

Short description: none

Telescopes with aperture diameter >8 metres

Gran Telescopio Canarias

W. M. Keck Observatory

Subaru Telescope

Hobby–Eberly Telescope

Large Binocular Telescope

Very Large Telescope

Southern African Large Telescope

Gemini Observatory

Gemini Observatory

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.

## Contents

* 1 Table of reflecting telescopes
* 2 Chronological list of largest telescopes
* 3 Future telescopes
* 3.1 Under construction
* 3.2 Proposed
* 4 See also
* 5 References
* 6 Further reading
* 7 External links

## Table of reflecting telescopes

Further information: Astronomy:List of large optical 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

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Large Binocular Telescope (LBT) |  | 11.9 m (469 in) (combined)[2] | Multiple
Two 8.4 m (331 in) mirrors | United States , Italy, Germany | Mount Graham International Observatory, Arizona, USA | 2004
Gran Telescopio Canarias (GTC) |  | 10.4 m (409 in) | Segmented
36 hexagonal segments | Spain , Mexico, United States | 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 | United States , Germany | McDonald Observatory, Texas , USA | 1997
Aperture increased 2015
Keck 1 |  | 10 m (394 in) | Segmented
36 hexagonal segments | United States | Mauna Kea Observatories, Hawaii, USA | 1993
Keck 2 |  | 10 m (394 in) | Segmented
36 hexagonal segments | United States | 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 , United States , United Kingdom , 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 | United States , United Kingdom , Canada, Chile , Australia, Argentina , Brazil | Mauna Kea Observatories, Hawaii, USA | 1999
Gemini South |  | 8.1 m (319 in) | Single | United States , United Kingdom , Canada, Chile , Australia, Argentina , Brazil | Cerro Pachón (CTIO), Coquimbo Region, Chile | 2001
James Webb Space Telescope |  | 6.5 m

(256 in)

| Segmented
18 hexagonal segments | NASA, ESA, CSA | Halo orbit around the Earth-Sun L2 Point | 2022
MMT (current optics) |  | 6.5 m (256 in) | Single | United States | F. L. Whipple Obs., Arizona, USA | 2000
Magellan 1 (Walter Baade)[5] |  | 6.5 m (256 in) | Single | United States | Las Campanas Obs., Atacama Region, Chile | 2000
Magellan 2 (Landon Clay) |  | 6.5 m (256 in) | Single | United States | 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 | United States | 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 | United States | 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 | United Kingdom , Netherlands, Spain | Roque de los Muchachos Obs., Canary Islands, Spain | 1987
SOAR |  | 4.1 m (161 in) | Single | United States , Brazil | Cerro Pachón (CTIO), Coquimbo Region, Chile | 2002
VISTA | File:VISTA at Paranal Eso0704b.tif | 4.1 m (161 in) | Single | ESO Countries, Chile | Paranal Observatory, Antofagasta Region, Chile | 2009
Víctor M. Blanco Telescope |  | 4 m (157 in) | Single | United States | 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 | United States | Kitt Peak National Obs., Arizona, USA | 1973
Daniel K. Inouye Solar Telescope |  | 4 m (157 in) | Single | United States | Haleakala Observatory, Hawaii, USA | 2019
Anglo-Australian Telescope (AAT) |  | 3.89 m (153 in) | Single | Australia, United Kingdom | Australian Astronomical Obs., New South Wales, Australia | 1974
United Kingdom Infrared Telescope (UKIRT) |  | 3.8 m (150 in) | Single | United Kingdom , United States | Mauna Kea Observatories, Hawaii, USA | 1979
3.67 m AEOS Telescope (AEOS) |  | 3.67 m (144 in) | Single | United States | 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 , United States | 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 | United States | Starfire Optical Range, New Mexico, USA | 1994
WIYN Telescope | Error creating thumbnail: Unable to save thumbnail to destination | 3.5 m (138 in) | Single | United States | Kitt Peak National Obs., Arizona, USA | 1994
Space Surveillance Telescope |  | 3.5 m (138 in) | Single | United States , 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 | United States | 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 | United States | Lick Observatory, California , USA | 1959
NASA Infrared Telescope Facility |  | 3.0 m (118 in) | Single | United States | Mauna Kea Observatory, Hawaii, USA | 1979
NASA-LMT |  | 3 m (118 in) | Liquid | United States | 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, USA.[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 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)

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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 telescopes

### Under construction

The Extremely Large Telescope under construction, 2 August 2023

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

* Extremely Large Telescope, Chile – 39.3 m (1,550 in). Construction began in 2018, first light planned in 2028.[22]
* Thirty Meter Telescope, Hawaii, USA – 30 m (1,200 in). Construction began in 2014 but halted in 2015; as of 2022[update] 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]
* Tokyo Atacama Observatory (TAO) – 6.5 m (260 in). First light planned for 2023.[27]
* 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[28] and has not resumed.
* Timau National Observatory, Indonesia – 3.8 m (150 in). Construction expected to be completed in 2023.[29]

### Proposed

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:

* Large UV Optical Infrared Surveyor (LUVOIR), a proposed space telescope for launch in the mid 2030s.
* MUltiplexed Survey Telescope (MUST), a 6.5 m spectroscopic survey telescope.[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]
* Advanced Liquid-mirror Probe of Astrophysics, Cosmology and Asteroids (ALPACA), a proposed Earth-based 8 metre telescope, by Arlin Crotts of Columbia University.[33][34]

## See also

* List of largest infrared telescopes
* List of telescope types
* Lists of telescopes

## References

1. ↑ "Neptune from the VLT and Hubble" (in en). https://www.eso.org/public/images/eso1824c/.
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". https://mcdonaldobservatory.org/news/releases/20151102.
4. ↑ "Howstuffworks "10 Amazing Telescopes"". Science.howstuffworks.com. http://science.howstuffworks.com/ten-amazing-telescopes.htm/printable.
5. ↑ "The Carnegie Observatories – Magellan Telescopes". Carnegie Institution for Science. http://obs.carnegiescience.edu/Magellan.
6. ↑ Andersen, Geoff. The Telescope, p. 165
7. ↑ [1]
8. ↑ "LAMOST Homepage – Gallery". Lamost.org. August 13, 2012. http://www.lamost.org/public/gallery.
9. ↑ Dwayne DayMonday, May 11, 2009 (2009-05-11). "Mirrors in the dark". The Space Review. http://www.thespacereview.com/article/1371/1.
10. ↑ Lowell Observatory – 4.3-meter DCT
11. ↑ "The Mayall 4-Meter Telescope". Noao.edu. February 27, 1973. http://www.noao.edu/outreach/kptour/mayall.html.
12. ↑ Sagar, Ram; Kumar, Brijesh; Omar, Amitesh; Pandey, A. K. (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. doi:10.1117/12.925634. Bibcode: 2012SPIE.8444E..1TS.
13. ↑ "Max-Planck-Institut für Astronomie". Mpia.de. July 20, 1994. http://www.mpia.de/Public/menu_q2.php?Aktuelles/PR/2004/PR041116/PR_041116_en.html.
14. ↑ Pike, John. "Starfire". Globalsecurity.org. http://www.globalsecurity.org/space/systems/starfire.htm.
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. https://www.science.org/content/article/door-open-iranian-astronomers-seek-collaborations-their-new-world-class-telescope.
16. ↑ "NASA Orbital Debris Observatory". Astro.ubc.ca. http://www.astro.ubc.ca/lmt/Nodo/index.html.
17. ↑ "Polissage Optique pour les Grands Instruments de la Physique et de l 'Astronomie". http://www.rdv-routedeslasers.com/polissage/tele/interventions/8_E_Ruch_SAGEM_REOSC.pdf.
18. ↑ "Mirror Castings". Steward Observatory Mirror Lab. https://mirrorlab.arizona.edu/content/mirror-castings.
19. ↑ "Large Optics Manufacturing in Large Optics Manufacturing in Lytkarino Optical Glass Factory, Russia". http://www.opticinnovations.co.uk/attachments/article_with_pdf_attachments/Large size and high aperture optics produced by LZOS .pdf.
20. ↑ "SUBARU Telescope 8.3m Primary Mirror Finished". http://carlkop.home.xs4all.nl/subaru.html.
21. ↑ "Keck Telescope Facts". Spacecraftkits.com. http://spacecraftkits.com/KFacts.html.
22. ↑ "Timeline". European Southern Observatory. https://elt.eso.org/about/timeline/.
23. ↑ "Timeline". TMT International Observatory. https://www.tmt.org/page/timeline.
24. ↑ "Quick Facts". Gmto.org. https://www.gmto.org/overview/quick-facts/.
25. ↑ "Construction Project Status". Rubin Observatory. 16 October 2022. https://www.lsst.org/about/project-status. "14-Mar-2024 System First Light"
26. ↑ Universities in U.S. and Mexico Partner on Telescope Project. Arizona Public Media, 13 November 2017.
27. ↑ Yoshii, Y.; Doi, M.; Kohno, K.; Miyata, T.; Motohara, K.; Kawara, K.; Tanaka, M.; Minezaki, T. et al. (2016). "The University of Tokyo Atacama Observatory 6.5m telescope: Project overview and current status". Ground-Based and Airborne Telescopes VI 9906: 99060R. doi:10.1117/12.2231391. Bibcode: 2016SPIE.9906E..0RY.
28. ↑ Creech-Eakman, Michelle J.; Romero, V. D.; Haniff, Christopher A.; Buscher, David F.; Young, J. S.; Olivares, Andres; Ligon, E. R.; Payne, I. et al. (13 December 2020). "Setting the stage for first fringes with the Magdalena Ridge Observatory Interferometer". Optical and Infrared Interferometry and Imaging VII. 11446. p. 1144609. doi:10.1117/12.2563173. Bibcode: 2020SPIE11446E..09C. https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11446/2563173/Setting-the-stage-for-first-fringes-with-the-Magdalena-Ridge/10.1117/12.2563173.short.
29. ↑ "Pembangunan Observatorium Nasional Timau segera Rampung" (in id-ID). 2023-07-30. https://www.brin.go.id/news/113812/pembangunan-observatorium-nasional-timau-segera-rampung.
30. ↑ Zhang, Yifan; Jiang, Haijiao; Shectman, Stephen; Yang, Dehua; Cai, Zheng; Shi, Yong; Huang, Song; Lu, Lu et al. (2023). "Conceptual design of the optical system of the 6.5m wide field multiplexed survey telescope with excellent image quality". PhotoniX 4 (4): 16. doi:10.1186/s43074-023-00094-4. https://www.researchsquare.com/article/rs-2136738/latest.pdf.
31. ↑ "Introduction to the Chinese Giant Solar Telescope". http://www.ncra.tifr.res.in:8081/~basi/ASICS_2/031-Deng.pdf.
32. ↑ Staff (29 August 2012). "China Exclusive: Scientists looking for site for giant solar telescope". http://www.spacedaily.com/reports/China_Exclusive_Scientists_looking_for_site_for_giant_solar_telescope_999.html.
33. ↑ Shiga, David (2 June 2008). "Liquid-mirror telescopes are a reality at last". New Scientist. https://www.newscientist.com/article/dn14030-liquid-mirror-telescopes-are-a-reality-at-last/.
34. ↑ "Advanced Liquid-mirror Probe of Astrophysics, Cosmology and Asteroids)". Astronomy and Astrophysics at the University of British Columbia. https://www.astro.ubc.ca/LMT/alpaca/index.html.

## Further reading

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

## 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)

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