List of largest optical reflecting telescopes

This list of the largest optical reflecting telescopes with objective diameters of 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. Another advantage of Earth based telescopes is the comparatively low cost of upgrading and replacing instruments.

Table of reflecting telescopes

Telescopes in this list are ordered by effective optical aperture, given as the diameter of a circle with equivalent collecting area. Aperture has historically been a useful gauge of telescopes' limiting resolution, optical area, physical size, and cost. Multiple mirror or segmented mirror telescopes that are on the same mount and usually form a single combined image are ranked by their equivalent combined aperture. Telescopes that cannot use their entire primary mirror at once (e.g. HET or LAMOST) are listed by their maximum effective aperture. Telescopes that are sometimes used for optical interferometry are listed individually, not as a combined instrument. All telescopes with an effective aperture of at least at visible or near-infrared wavelengths are included; selected smaller telescopes are listed elsewhere.

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|+Reflecting telescopes

! Name || class="unsortable"| Image ||data-sort-type="number"| Effective aperture || Mirror type || Nationality / Sponsors || Site || First light

| Large Binocular Telescope (LBT) || 50px || (combined)||Multiple Two mirrors|| USA, Italy, Germany || Mount Graham International Observatory, Arizona, USA || 2005

| Gran Telescopio Canarias (GTC) || 50px || || Segmented 36 hexagonal segments || Spain, Mexico, USA || Roque de los Muchachos Obs., Canary Islands, Spain || 2006

| Hobby–Eberly Telescope (HET) || 50px || (effective) || Segmented 91 × hexagonal segments forming an 11 m × 9.8 m mirror || USA, Germany || McDonald Observatory, Texas, USA || 1997 Aperture increased 2015

| Keck 1 || 50px || || Segmented 36 hexagonal segments || USA || Mauna Kea Observatories, Hawaii, USA || 1993

| Keck 2 || 50px || || Segmented 36 hexagonal segments || USA || Mauna Kea Observatories, Hawaii, USA || 1996

| Southern African Large Telescope (SALT) || 50px || (effective) || Segmented 91 × 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) || 50px || || Single || Japan || Mauna Kea Observatories, Hawaii, USA || 1999

| VLT UT1 – Antu || 50px || || Single || ESO Countries, Chile || Paranal Observatory, Antofagasta Region, Chile || 1998

| VLT UT2 – Kueyen || 50px || || Single || ESO Countries, Chile || Paranal Observatory, Antofagasta Region, Chile || 1999

| VLT UT3 – Melipal || 50px || || Single || ESO Countries, Chile || Paranal Observatory, Antofagasta Region, Chile || 2000

| VLT UT4 – Yepun || 50px || || Single || ESO Countries, Chile || Paranal Observatory, Antofagasta Region, Chile || 2001

| Gemini North || 50px || || Single || USA, UK, Canada, Chile, Australia, Argentina, Brazil || Mauna Kea Observatories, Hawaii, USA || 1999

| Gemini South || 50px || || Single || USA, UK, Canada, Chile, Australia, Argentina, Brazil || Cerro Pachón (CTIO), Coquimbo Region, Chile || 2001

| James Webb Space Telescope

| 50px

| 6.5 m

(256 in)

| Segmented 18 hexagonal segments

| NASA, ESA, CSA

| Halo orbit around the Earth-Sun L2 Point

| 2022

| MMT (current optics) || 50px || || Single || USA || F. L. Whipple Obs., Arizona, USA || 2000

| Magellan 1 || 50px || || Single || USA || Las Campanas Obs., Atacama Region, Chile || 2000

| Magellan 2 || 50px || || Single || USA || Las Campanas Obs., Atacama Region, Chile || 2002

|Tokyo Atacama Observatory (TAO)

|Single

|Japan

|Cerro Chajnantor, Atacama Desert, Chile

|2024

| Simonyi Survey Telescope || 50px || (effective) || Combined primary & tertiary mirror Total diameter || Maple Ridge, British Columbia, Canada || 2003 Decommissioned 2016

| Hale Telescope || 50px || || Single || USA || Palomar Observatory, California, USA || 1949

| LAMOST || 50px || (effective)|| 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 || China || Beijing Astronomical Obs., Xinglong, China || 2008

| MMT (original optics) || 50px|| (combined) || Multiple Six mirrors || USA || F. L. Whipple Obs., Arizona, USA || 1979 Mirrors removed 1998

| Lowell Discovery Telescope|| 50px || || Single || USA || Lowell Observatory, Happy Jack, Arizona, USA || 2012

| William Herschel Telescope || 50px || || Single || UK, Netherlands, Spain || Roque de los Muchachos Obs., Canary Islands, Spain || 1987

| SOAR || 50px || || Single || USA, Brazil || Cerro Pachón (CTIO), Coquimbo Region, Chile || 2002

| VISTA || 50px || || Single || ESO Countries, Chile || Paranal Observatory, Antofagasta Region, Chile || 2009

| Víctor M. Blanco Telescope || 50px || || Single || USA || Cerro Tololo Inter-American Obs., Coquimbo Region, Chile || 1976

| International Liquid Mirror Telescope ||  || || Liquid || Belgium, Canada, India, Poland || ARIES Devasthal Observatory, Nainital, India|| 2022

| Nicholas U. Mayall 4 m || 50px || || Single || USA || Kitt Peak National Obs., Arizona, USA || 1973

| Daniel K. Inouye Solar Telescope || 50px || || Single || USA || Haleakala Observatory, Hawaii, USA || 2019

| DAG Telescope || || || Single || Turkey|| Eastern Anatolia Observatory, Erzurum, Turkey || 2025

| Anglo-Australian Telescope (AAT) || 50px || || Single || Australia, UK || Australian Astronomical Obs., New South Wales, Australia || 1974

| United Kingdom Infrared Telescope (UKIRT) || 50px || || Single || UK, United States || Mauna Kea Observatories, Hawaii, USA || 1979

| 3.67 m AEOS Telescope (AEOS) || 50px || || Single || USA || Air Force Maui Optical Station, Hawaii, USA || 1996

| 3.6 m Devasthal Optical Telescope (DOT) || 50px|| || Single || India || ARIES Devasthal Observatory, Nainital, India|| 2016

| Telescopio Nazionale Galileo (TNG) || 50px || || Single || Italy || Roque de los Muchachos Obs., Canary Islands, Spain || 1997

| New Technology Telescope (NTT) || 50px || || Single || ESO countries || La Silla Observatory, Coquimbo Region, Chile || 1989

| Canada-France-Hawaii Telescope (CFHT) || 50px || || Single || Canada, France, USA || Mauna Kea Observatories, Hawaii, USA || 1979

| ESO 3.6 m Telescope || | 50px || || Single || ESO countries || La Silla Observatory, Coquimbo Region, Chile || 1977

| MPI-CAHA 3.5 m || 50px || || Single || West Germany, Spain || Calar Alto Obs., Almería, Spain || 1984

| USAF Starfire 3.5 m|| | 50px || || Single || USA || Starfire Optical Range, New Mexico, USA || 1994

| WIYN Telescope || 50px || || Single || USA || Kitt Peak National Obs., Arizona, USA || 1994

| Space Surveillance Telescope || 50px || || Single || USA, 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) || 50px || || Single || USA || Apache Point Obs., New Mexico, USA || 1994

|Iranian National Observatory (INO340) ||left|61x61px||||Single||Iran||Mount Gargash, Isfahan Province, Iran ||2022

| Shane Telescope || 50px || || Single || USA || Lick Observatory, California, USA || 1959

| NASA Infrared Telescope Facility || 50px || || Single || USA || Mauna Kea Observatory, Hawaii, USA || 1979

| NASA-LMT || 50px || || Liquid|| USA || NASA Orbital Debris Obs., New Mexico, USA || 1995 Decommissioned 2002

|- class="sortbottom"

|colspan=8 style="padding: 8px; background-color: #f2f2f2; text-align: center;" | For continuation of this list, see List of large optical reflecting telescopes

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.

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|+Reflecting telescopes (chronologically)

! Years Largest || Name || Out || In || Aperture (m) || Area (m2) || M1 Mirror || Note || Altitude (m)

| 2009–Present || Gran Telescopio Canarias || 50px || 50px || 10.4 || 74 || 36 × 1.9 m hexagons M1 mirror || Segmented mirror || 2267

| 1993–2009 || Keck 1 || 50px || 40px || 10 || 76 || 36 × 1.8 m hexagons M1 mirror || Segmented mirror, M1 f/1.75 || 4145

| 1976–1993 || BTA-6 || 50px || 50px || 6 || 26 || 605 cm f/4 M1 mirror || Mirror replaced twice || 2070

| 1948–1976 || Hale (200 inch) || 50px || 50px || 5.1 || – || 508 cm f/3.3 M1 mirror || || 1713

| 1917–1948 || Hooker (100 inch) || || 30px || 2.54 || – || || Also used for 1st optical interferometer || 1742

|- class=sortbottom

|colspan=9|For earlier entries, see List of largest optical telescopes historically

thumb|450px|center|Large reflecting telescopes over time. The horizontal axis indicates the year built and the vertical axis is the size of the mirror measured in meters. Selected countries are color-coded (see legend).

Future telescopes

Under construction

thumb|upright=1.6|The [[Extremely Large Telescope under construction in November 2025]]

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

Extremely Large Telescope, Chile – . Construction began in 2018, first light planned in 2029.
Thirty Meter Telescope, Hawaii, USA – . Construction began in 2014 but halted in 2015; it has not resumed.
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.
San Pedro Martir Telescope, Baja California, Mexico – . First light planned in 2023.
Magdalena Ridge Observatory Interferometer, New Mexico, USA – An optical interferometer array with ten telescopes. The light gathering power is equivalent to a single aperture. The first telescope was installed in 2016; construction was paused in 2019 due to insufficient funding and has not resumed.
Timau National Observatory, Indonesia – . Construction expected to be completed by early 2025.

Proposed

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

Habitable Worlds Observatory (LUVOIR), a proposed space telescope for launch in the early 2040s.
MUltiplexed Survey Telescope (MUST), a 6.5 m spectroscopic survey telescope.
Chinese Giant Solar Telescope (CGST), an infrared and optical solar telescope, with light-gathering power equivalent to a 5 m diameter aperture.

References

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)