Question: What is the largest telescope in the world?

List of largest optical reflecting telescopes


This list of the largest optical reflecting telescopes with objective diameters of 3.0 metres (120in) or greater is sorted by aperture, which is one limit on the light-gathering power and resolution of a reflecting telescope's optical assembly. The mirrors themselves can be larger than the aperture, and telescopes may use aperture synthesis achieved by 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 85m) can reach very high 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 (22.8m) 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 time. Location in the northern or southern hemisphere of the Earth can also limit what part of the sky can be observed.
Table of reflecting 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, may have a working beam combiner, and can form an image may be ranked by an equivalent aperture to this reported by sources. HET-style or fixed telescopes are ranked by an equivalent aperture also.

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.[15] The Steward Observatory Mirror Lab cast and polished the two LBT mirrors, the two Magellan mirrors and the MMT replacement mirror. It is currently making the LSST primary mirror and the mirrors for the Giant Magellan Telescope.[16] The Keck segments were made by Schott AG. The SALT and LAMOST segments were cast and polished by LZOS.[17] The mirror for Subaru was cast by Corning and polished at Contraves Brashear Systems in Pennsylvania.[18]
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.



Chronological list of largest telescopes
These telescopes were the largest in the world at the time of their construction.



For earlier top telescopes see List of largest optical telescopes historically
Future telescopes

Below are selected telescopes that are still in the conceptual/proposed stage or still under construction.
Under construction or planned construction
European Extremely Large Telescope 39.3m (first light planned for 2024)[20]
Thirty Meter Telescope 30 m (construction halted since April 2015 due to a permit dispute; first light was planned for 2022 when construction halted)[21]
Giant Magellan Telescope 7 × 8.4m mirrors giving a 24.5 m aperture with 21.4 m light gathering area (first light planned in 2021 and completion in 2025)[22][23]
Large Synoptic Survey Telescope 8.4 m (first light planned in 2019 and full operations beginning in 2022)
James Webb Space Telescope 6.5 m (March 2021 launch planned)[24]
Pan-STARRS 4 × 1.8 m (2 of 4 complete)
Magdalena Ridge Observatory Telescope Array 10 × 1.4 m
Daniel K. Inouye Solar Telescope 4 m (construction started in 2013)
International Liquid Mirror Telescope 4 m (dome construction in Devasthal, India, started in 2013)[25]
San Pedro Martir Telescope 6.5m (completion expected by 2023)[26]
Iranian National Observatory 3.4m (first light planned in 2020) [27]
Proposed

Large UV Optical Infrared Surveyor (LUVOIR), a proposed space telescope for launch in the mid 2030s. There are several designs under study with 8–15m diameter, including the Advanced Technology Large-Aperture Space Telescope (ATLAST) and High-Definition Space Telescope (HDST)
Chinese Giant Solar Telescope (CGST), an infrared and optical solar telescope, with light-gathering power equivalent to a 5m diameter aperture [28][29]
Colossus Telescope - proposed 70-80 meter diameter telescope for examining exoplanets (2010s)

See also

Extremely large telescope
List of largest optical refracting telescopes
List of optical telescopes
List of astronomical interferometers at visible and infrared wavelengths
List of largest optical telescopes historically
List of largest optical telescopes in the 20th century
List of largest optical telescopes in the 19th century
List of largest optical telescopes in the 18th century
Strehl ratio


Further reading
"The Astronomical Scrapbook", Joseph Ashbrook, Sky Publishing Corporation 1984, ISBN0-933346-24-7, o
"Giant Telescopes of the World", Sky and Telescope, August 2000.
"The History of the Telescope", Henry C. King. (1955)
"The Historical Growth of Telescope Aperture", René Racine, Publications of the Astronomical Society of the Pacific, 116
JRASC (1929) vol 23, p351
Sky&Telescope (April 1981) p303
Sky&Telescope (July 1993) vol 86, p 27-32
James H. Burge, 1993 Dissertation at UA, "Advanced Techniques for Measuring Primary Mirrors for Astronomical Telescopes"
CS1 maint: multiple names: authors list (link)