List of largest optical telescopes in the 20th century

The following is a list of the largest optical telescopes in the 20th century, paying special attention to the diameter of the mirror or lens of the telescope's objective, or aperture. Aperture rank currently goes approximately by the usable physical aperture size and not by aperture synthesis, although interferometers attained some of the highest angular resolutions at visible and infrared wavelengths compared to traditional telescopes. Diverging methods of construction and use for reflecting telescopes in that area make comparing synthesized aperture irregular.

For instance, Keck I or II alone has less angular resolution than the Keck Interferometer (Keck I & II together), however, the Keck Interferometer is used for a much narrower range of type of observations. Ultimately, a valid comparison between two telescopes must take into consideration more specifications, when a general measurement becomes obtuse.

Aperture of the primary mirror alone can be poor measure of a reflective telescope's significance; for example, the Hubble Space Telescope has only a 2.4 metres (94 in) primary mirror. In addition, many large or significant telescopes are not optical and/or reflecting. However, many famous optical telescopes have had large apertures on their primary mirror with corresponding good angular resolution.

The list includes optical observatories, including UV, visible and some optical infrared telescopes, and near infrared. The list covers from about 1901 to 2001, with some flexibility to accommodate ambiguity in classification, for example some 2002 telescopes, if it was nearly operation in 2001. 19th century and earlier telescopes that ceased operation are not included, but the list is not complete.


Table of optical telescopes

Multiple mirror telescopes are ranked by their equivalent optical area, not peak interferometric aperture unless it is not relevant for the design. See also List of astronomical interferometers at visible and infrared wavelengths.

See also List of largest optical refracting telescopes, as this list does yet not include such large refractors as the Yerkes Observatory.

Name/Observatory Aperture
m
Aper.
in
Mirror type Nationality of Sponsors Site and/or Observatory FL or Built Image
Keck 1 10 m 394″ Segmented, 36 United States Mauna Kea Observatory, Hawaii 1993
Keck 2 10 m 394″ Segmented, 36 United States Mauna Kea Observatory, Hawaii 1996
Hobby–Eberly Telescope (HET) 9.2 m 362″ Segmented,91 United States, 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) 8.2 m 323″ Single ESO Countries + Chile Paranal Observatory, Chile 1999
VLT 3 (Melipal) 8.2 m 323″ Single ESO Countries + Chile Paranal Observatory, Chile 2000*
VLT 4 (Yepun) 8.2 m 323″ Single ESO Countries + Chile Paranal Observatory, Chile 2001*
Gemini North (Gillett) 8.1 m 318″ Single United States, Canada, Chile, Australia, Argentina, Brazil Mauna Kea Obs., Hawaii 1999
Gemini South 8.1 m 318″ Single United States, Canada, Chile, Australia, Argentina, Brazil Cerro Pachón, Chile 2001
MMT 6.5 m 256″ Single United States F. L. Whipple Obs., Arizona 2000
Magellan 1 (Walter Baade) 6.5 m 256″ Honeycomb United States Las Campanas Obs., Chile 2000
Magellan 2 (Landon Clay) 6.5 m 256″ Honeycomb United States Las Campanas Obs., Chile 2002*
BTA-6 6 m 238″ Single USSR + Russia Zelenchukskaya, Caucasus 1976
Hale Telescope (200 inch) 5.08 m 200″ Single United States Palomar Observatory, California 1948
MMT (original) (6 × 1.8 m) optics replaced 4.7 m (6 × 1.8 m) 186″ 6 mirrors United States F. L. Whipple Obs., Arizona 1979–1998
William Herschel Telescope 4.2 m 165″ Single UK, Netherlands, Spain ORM, Canary Islands 1987
SOAR 4.1 m 161″ Single United States, Brazil Cerro Pachón, Chile 2002*
Nicholas U. Mayall 4m 4 m 158″ Single USA Kitt Peak National Obs.; Arizona 1973
Victor M. Blanco Telescope 4 m 158″ 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
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) 3.67 m 145″ Single United States Air Force Maui Optical Station; Haleakala, Hawaii 1996
Telescopio Nazionale Galileo (TNG) 3.58 m 138″ Single Italy ORM; 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, United States 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 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 3.5 m 138″ Single USA Kitt Peak National Obs., USA 1994
Astrophysical Research Consortium (ARC) 3.48 m 137″ Single USA Apache Point Obs.; Sacramento Peak, New Mexico 1994
Infrared Telescope Facility (IRTF) 3.2 m 126″ Single IR United States Mauna Kea, Hawaii 1979
Shane Telescope 3.05 m 120″ Single United States Lick Observatory; Mt. Hamilton, California 1959
NASA-LMT (NODO) retired 3 m 118″ Liquid USA Sacramento Peak, New Mexico, USA 1995–2002
Harlan J. Smith Telescope 2.72 m 107″ Single USA McDonald Observatory, Texas, USA 1969-
UBC-Laval LMT 2.65 m 104″ Liquid Canada Vancouver, Canada 1992–
Shajn 2.6m (Crimean 102 in) 2.64 m 103″ Single Crimean Astrophysical Obs., Ukraine 1961
BAO 2.6 2.6 m 102″ Single Byurakan Astrophysical Obs.; Mt. Aragatz, Armenia 1976
Nordic Optical Telescope (NOT) 2.56 m 101″ Single Denmark, Sweden, Iceland, Norway, Finland La Palma, Canary Islands 1988
Isaac Newton Telescope (INT) 2.54 m 100″ Zerodur UK La Palma, Canary Islands moved/new mirror 1984
du Pont 2.54 m 100″ Single USA Las Campanas Observatory, Chile 1976
Hooker 100-Inch Telescope 2.54 m 100″ Single United States Mt. Wilson Observatory; California 1917
Sloan DSS 2.5 m 98″ Single United States Sacramento Peak, New Mexico 1997
Isaac Newton Telescope (INT) 2.54 m 98″ Single UK RGO, Sussex, England (original) 1965–1979
Hiltner Telescope 2.4 m 95″ Single United States MDM Observatory, Kitt Peak, Arizona 1986
Hubble (HST) 2.4 m 94″ Single NASA+ESA Low Earth orbit 1990
Vainu Bappu 2.34 m 92″ Single Vainu Bappu Observatory, India 1986
WIRO 2.3 2.3 m 90.5″ Single USA Wyoming, USA 1977
ANU 2.3m ATT 2.3 m 90″ Single Australia Siding Spring Obs., Australia 1984
Bok Telescope (90-inch) 2.3 m 90″ Single USA Steward Obs., Kitt Peak, Arizona 1969
University of Hawaii 2.2 m 2.24 m 88″ Single USA Mauna Kea Observatories, Hawaii 1970
MPIA-ESO (ESO-MPI) 2.2 m 87″ Single West Germany Cerro La Silla, Chile 1984
MPIA-CAHA 2.2m 2.2 m 87″ Single West Germany Calar Alto Observatory, Spain 1979
Xinglong 2.16m 2.16 m 85″ Single PRC (China) Xinglong, China 1989
Jorge Sahade 2.15m 2.15 m 84″ Single Leoncito Astronomical Complex, Argentina 1987
INAOE 2.12 (OAGH) 2.12 m 83″ Single Mexico, USA Guillermo Haro Observatory; Sonora 1987
UNAM 2.12 2.12 m 83" Single NAO; San Pedro, Mexico 1979
Kitt Peak 2.1-meter 2.1 m 83″ Single USA Kitt Peak (KNPO), USA 1964
Otto Struve Telescope 2.1 m 82 Single USA McDonald Observatory, USA 1939
Himalayan Chandra Telescope (HCT) 2.01 m 79″ Single India Indian Astronomical Obs., Hanle (4500 m) 2000
Alfred Jensch Teleskop 2 m 79″ Single Karl Schwarzschild Observatory 1960
Carl Zeiss Jena 2 m 79″ Single Shamakhi Astrophysical Obs., Azerbaijan 1966
Ondřejov 2-m [1] 2 m 79″ Single Czechoslovakia Ondřejov Observatory, Czechia 1967
Ritchey-Chretien-Coude (RCC) 2 m 79″ Single Rozhen Observatory, Bulgaria 1984
Carl Zeiss Jena 2 m 79″ Single Main Ukraine Obs.
Bernard Lyot Telescope 2 m 79″ Single France Pic du Midi Obs., France 1980
Faulkes Telescope South 2 m 79″ Single UK Siding Spring Obs., Australia 2001
MAGNUM 2 m 79″ Single IR Japan Haleakala Obs., USA 2001
OHP 1.93 1.93 m 76″ Single France Haute-Provence Observatory, France 1958
74-inch Radcliffe Telescope (1.9 m) 1.88 m 74″ Single South African Astronomical Obs., Sutherland, 1974–Present
Radcliffe Obs.,1948– 1974
1950
188 cm telescope 1.88 m 74″ Single Japan Okayama Astrophysical Observatory, Japan 1960
DDO 1.88 m 1.88 m 74″ Single Canada David Dunlap Observatory, Ontario 1935
74" reflector 1.88 m 74″ Single Australia Mount Stromlo Observatory, Australia 1955–2003
Kottamia telescope 1.88 m 1.88 m 74″ Single Egypt Egypt 1960
Vatican Advanced Technology Telescope (VATT) 1.83 m 72″ Single Vatican City Mt. Graham International Obs., Arizona 1993
72-Inch Perkins Telescope 1.83 m 72″ Single USA Lowell Observatory, Anderson Mesa USA 1964
Plaskett telescope 1.83 m 72″ Single Canada Dominion Astrophysical Observatory, Canada 1918
Copernico 182 cm 1.82 m 72″ Single Italy Asiago Observatory, Italy (1350 m) 1973
1.8m Ritchey Cretien reflector 1.8 m 72″ Single Korea Bohyunsan Optical Astronomy Observatory, Korea 1996
Sandy Cross Telescope 1.8 m 71″ Single Canada Rothney Astrophysical Observatory 1996
Spacewatch 1.8-meter Telescope 1.8 m 71″ Single USA Kitt Peak National Observatory, USA 2001
69-inch Perkins Telescope 1.75 m 69″ Single USA Perkins Observatory, Ohio 1931–1964
165 cm telescope 1.65 m 65″ Single Moletai Astronomical Obs., Lithuania 1991
McMath–Pierce Solar Telescope 1.61 m 63″ Single USA Kitt Peak National Obs., USA 1962
AZT-33 1.6 m 63″ Single Sayan Solar Obs., Siberia (2000m) 1981
1.6 m Perkin Elmer 1.6 m 63″ Single Brazil Pico dos Dias Observatory 1981
1.6 1.6 m 63″ R/C Canada Mont Mégantic Observatory, Canada 1978
Kaj Strand Telescope 1.55 m 61″ Single USA USN Obs. Flagstaff Station, USA 1964
61" Kuiper Telescope 1.55 m 61″ Single USA Steward Obs., Mt. Bigelow, USA 1965
Oak Ridge Observatory 61" reflector (Wyeth) 1.55 m 61″ Single USA Oak Ridge Observatory, Massachusetts, USA 1933–2005
Estación Astrofísica de Bosque Alegre 1.54 m 60.6″ Single Argentina Estación Astrofísica de Bosque Alegre, Argentina 1942
Danish 1.54 meter telescope 1.54 m 60.6″ Single Denmark La Silla Observatory, Chile 1979
Harvard 60-inch Reflector 1.524 m 60″ Single United States Harvard College Observatory, USA 1905–1931
60-Inch Telescope 1.524 m 60″ Single United States Mt. Wilson Observatory; California 1908
Dunn Solar Telescope ex-VTT 1.524 m 60″ Single USA National Solar Obs.-Sacramento Peak, USA 1969
Palomar Observatory 60-inch 1.524 m 60″ Single USA Palomar Observatory, California, USA 1970
FLWO 1.5m Tillinghast 1.52 m 60″ Single United States F. L. Whipple Obs., Arizona 1994
Telescopio Carlos Sánchez (TCS) 1.52 m 60″ Single UK + Spain Teide Observatory, Tenerife (Spain) 1971
OHP 1.52 1.52 m 60″ Single France Haute-Provence Obs., France 1967
Mt. Lemmon 60" Telescope 1.52 m 60″ Single USA Steward Observatory, Mount Lemmon, USA 1970
OAN 1.52 m 1.52 m 60″ Single Spain Calar Alto Observatory, Spain 1970s
152 cm G.D. Cassini 1.52 m 60″ Single Italy Mount Orzale, Italy 1976
TIRGO (Gornergrat Infrared Telescope) 1.50 m 59″ Single IR Italy + Switzerland Hochalpine Forschungsstation Jungfraujoch und Gornergrat, Alps, Switzerland (3150 m) 1979–2005
AZT-22 1.5 m 59″ Single USSR, Uzbekistan Mount Maidanak, Uzbekistan 1972
AZT-20 1.5 m 59″ Single Assy-Turgen Observatory, Kazakhstan
AZT-12 1.5 m 59″ Single USSR, Estonia Tartu Observatory, Estonia 1976
RTT-150 1.5 m 59″ Single Russia, Turkey TÜBİTAK National Observatory, Turkey 2001
OSN 1.5m (Nasmyth) 1.5 m 59″ Single Spain Sierra Nevada Obs., Spain (2896 m) 1991
BST-1M 1.5 m 59″ Single IR USSR Salyut 6, Earth Orbit 1977–1982
USNOFS 1.3m 1.3 m 51″ Single USA USN Obs. Flagstaff Station, USA 1998
Warsaw Telescope 1.3 m 51″ Single Poland Las Campanas Obs., Chile 1996
Skinakas 1.3m Telescope 1.3 m 51'' Single Greece Skinakas Obs., Greece 1995
McGraw-Hill Telescope 1.27 m 50″ Single USA MDM Observatory, Arizona (1975–Present)
Stinchfield Woods, Michigan (1969–1975)
1969
Great Melbourne Telescope (refit) 127 cm 50″ Single Australia Mount Stromlo Observatory, Australia 1961–1973
1992–2003
AZT-11 1.25 m 49″ Single Abastumani Obs., Georgia (country) 1976
AZT-11 1.25 m 49″ Single Crimean Astrophysical Obs., Ukraine 1981
MPIA 1.2 1.23 m 48.4″ Single West Germany + Spain Calar Alto Obs., Spain 1975
Babelsberg Zeiss 1.22 m 48″ Single Germany, USSR Babelsberg Observatory; Berlin, Germany, Crimean Astrophysical Observatory (1952–present) 1924
Galileo 122 cm 1.22 m 48″ Single Italy Asiago Observatory, Italy 1942
Samuel Oschin telescope 1.22 m 48″ Schmidt USA Palomar Observatory; California 1948
OHP 1.20 1.2 m 48″ Single France Haute-Provence Obs., France 1943
Paris 48″ Reflector 1.2 m 48″ France Paris Observatory, France 1871–1943
Great Melbourne Telescope 122 cm 48″ reflector – metal Australia Melbourne Observatory, Australia 1878–1944
Oskar-Lühning Telescope 1.2 m 47″ Single Germany Hamburg-Bergedorf Obs., Germany 1975
Leonhard Euler Telescope 120 cm 47″ Single Switzerland La Silla, Chile 1998
Mercator Telescope 120 cm 47″ Single Belgium+Switzerland ORM; La Palma, Canary Islands 2001
Hamburg Robotic Telescope (HRT) 120 cm 47″ Single Germany Hamburg-Bergedorf Obs., Germany 2002*
Hänssgen's reflector 107 cm 42″ Single Germany Mobile (~Germany) 2002*
Omicron@C2PU 104 cm 41" Single France Observatoire de la Côte d'Azur – Calern site, France, IAU code: 010 2013
Epsilon@C2PU 104 cm 41" Single France Observatoire de la Côte d'Azur – Calern site, France, IAU code: 010 2015
Grubb Parsons 40-inch 102 cm 40″ Single Sweden Stockholm Observatory in Saltsjöbaden 1930–present
Nickel Telescope 102 cm 40″ Single USA Lick Observatory, USA 1979
Grubb 40-inch 102 cm 40" Single USSR Crimean Astrophysical Observatory Simeiz (destroyed in WWII) 1925–1944
George Ritchey 40-inch (1 m) 102 cm 40″ R/C USA Flagstaff, Arizona (Washington, D.C. until 1955), USA 1934
Yerkes "41-inch" 102 cm 40″ Single USA Yerkes Observatory, USA 1968
Meudon Observatory 1m 100 cm 39.4″ Single France Meudon Observatory/ Paris Observatory 1891
ZIMLAT 100 cm 39.4″ Single Switzerland Zimmerwald Obs., Switzerland 1997
OGS Telescope 100 cm 39.4″ Single European Space Agency countries Teide Observatory, Tenerife, Spain 1995
Jacobus Kapteyn Telescope 100 cm 39.4″ Single UK + Netherlands Isaac Newton Group, Canary Islands 1984
Lulin One-meter Telescope (LOT) 100 cm 39.4″ Single ROC (Taiwan) Lulin Observatory, Taiwan 2002*
Zeiss di Merate (1m reflector) 100 cm 39.4″ Single Kingdom of Italy Merate Obs., Merate, Italy 1926
Zeiss 1m reflector 100 cm 39.4″ Single Belgium Royal Obs., Uccle, Belgium 1920s
Hamburg Spiegelteleskop (1m reflector) 100 cm 39.4″ Single Deutsches Reich (Germany) Hamburg-Bergedorf Obs., Germany 1911
1-m Carl Zeiss Jena 100 cm 39.4″ Single CCCP Assy-Turgen Observatory, Kazakhstan
James Gregory Telescope 94 cm 37" SCT Great Britain University of St Andrews, UK 1962
Schmidt 92/67 cm 92 cm 36″ Schmidt Italy Cima Ekar Observatory, Asiago, Italy (1360 m) 1966
Kuiper Airborne Obs.(KAO) 91.4 cm 36″ Single USA C-141 (mobile) 1974–1995
Stratoscope 2 91.4 cm 36″ Single USA Balloon (mobile) 1961–1973
Crossley Reflector 91.4 cm 36″ Single US+UK Lick Observatory, USA 1896
36-inch Yapp reflector 91.44 cm 36″ Reflector UK Greenwich & Herstmonceux 1932

This table does not include all the 20th 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.

Selected telescopes with apertures of 90 cm (35.4 in.) and smaller

Some famous 20th century regionally famous telescopes, space telescopes, or otherwise significant. (100 cm = 1 meter)

Name Aperture
m
Aper.
in
Mirror/type Nationality/Sponsors Site Built/Used
Hopkins Ultraviolet Telescope 90 cm 35.4" Single UV USA STS, Earth Orbit 1990, 1995
Meudon Great Refractor 83 cm 32.67" refractor (visual) France Meudon, France 1891
83-cm Reflector, Toulouse Observatory 83 cm 32.67" reflector-glass France Toulouse, France 1875
Focault 80 cm, Marseille Observatory 80 cm 31.5" reflector-glass Focault Marseille, France 1862–1965
Astron 80 cm 31.5" Single UV CCCP + France Earth orbit 1983–1989
Potsdam Great Refractor (double refractor) 80 cm 31.5" Doublet Germany Potsdam, Germany 1899
Ruisinger 76.2 cm 30" Single-Newtonian United States (ASKC) Louisburg, Kansas – Powell Obs. 1985
Greenwich 28-inch refractor
Royal Observatory, Greenwich
71 cm 28" Doublet British Empire Greenwich, England
Herstmonceux, England, UK
1893
Meudon Great Refractor 62 cm refractor (photographic-blue) France Meudon, France 1891
Infrared Space Observatory 60 cm 23.5" IR (2.4-240 μm) European Space Agency Earth orbit (GEO) 1995–1998
IRAS 57 cm 22.44" R/C IR US + UK + The Netherlands Earth orbit 1983
Mons Telescope 50 cm 19.7" Single Belgium Teide Observatory, Tenerife (Spain) 1972
Dutch Open Telescope (DOT) 45 cm 17.7" Solar Denmark ORM, Canary Islands 1997
Explorer 57 (IUE) 45 cm 17.7" Single UV US+UK+ESA Countries Earth orbit (GEO) 1978–1996
Glazar UV telescope 40 cm 15.75" Single UV CCCP Kvant-1 (Mir), Earth Orbit 1987–2001
Glazar 2 UV telescope 40 cm 15.75" Single UV CCCP + Switzerland Kristall (Mir), Earth Orbit 1990–2001
Mars Global Surveyor—MOC 35 cm 13.8" R/C USA Mars Orbit 1996–2006
Griffith Observatory 12-inch Zeiss refractor 30.5 cm 12" Achromat USA L.A., USA 1931
XMM-Newton—UV camera 30 cm 11.9" Single UV ESA Countries Earth orbit 1998
TRACE 30 cm 11.9" Single EUV/UV/Vis NASA Earth orbit 1998–2010
Hipparcos 29 cm 11.4" Schmidt European Space Agency Earth orbit (GTO) 1989–1993
Astronomical Netherlands Satellite 22 cm 8.7" Single UV Nederlands & USA Earth Orbit 1974–1976
Galileo – Solid State Imager 17.65 cm 6.95" Reflector USA Jupiter 1989–2003
Voyager 1/2, ISS-NAC 17.6 cm 6.92" Catadioptric USA Space 1977
Spacelab IRT 15.2 cm 6" IR (1.7–118 μm) ESA + NASA STS, Earth Orbit 1985
Mariner 10 – TV Photo. (x2) 15 cm 5.9" Reflector USA Space 1973–1975
Deep Space 1—MICAS 10 cm 3.94" Single USA Solar Orbit 1998–2001
Far Ultraviolet Camera/Spectrograph 7.62 cm 3" Schmidt UV USA Lunar surface 1972
Voyager 1/2, ISS-WAC 6 cm 2.36" Lens USA Space 1977

At the end of the 20th century preliminary designs for extremely large telescope of the 21st century were being worked on, as well as many smaller telescopes such as the Large Binocular Telescope

Under Construction

Examples of telescopes that were started in the 20th century, but may only have achieved a preliminary level of construction by the turn of the century.

Name/Observatory Aperture
m
Aper.
in
Mirror type | Nationality of Sponsors Site and/or Observatory FL or Built
GTC 10.4 m 409" Segmented,36 Spain (90%), Mexico(5%), USA(5%) Roque de los Muchachos Observatory, La Palma 2007
Faulkes Telescope North 2 m 79" Single UK Haleakala Observatory, Hawaii, USA 2003

Refractors

See also

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