For the specific observatory by this name, see Extremely Large Telescope.
An extremely large telescope (ELT) is an astronomical observatory featuring an optical telescope with an aperture for its primary mirror from 20 metres up to 100 metres across,[1][2] when discussing reflecting telescopes of optical wavelengths including ultraviolet (UV), visible, and near infrared wavelengths. Among many planned capabilities, extremely large telescopes are planned to increase the chance of finding Earth-like planets around other stars.[3] Telescopes for radio wavelengths can be much bigger physically, such as the 300 metres (330 yards) aperture fixed focus radio telescope of the Arecibo Observatory (now defunct). Freely steerable radio telescopes with diameters up to 100 metres (110 yards) have been in operation since the 1970s.
These telescopes have a number of features in common, in particular the use of a segmented primary mirror (similar to the existing Keck telescopes), and the use of high-order adaptive optics systems.[4][5]
Although extremely large telescope designs are large, they can have smaller apertures than the aperture synthesis on many large optical interferometers. However, they may collect much more light, along with other advantages.
^As A Skeleton Science Case For Extremely Large (20m–100m) Ground-based Telescopes (ELTs) and first section of ELT Roadmap Archived 2015-05-18 at the Wayback Machine, PDF
^Overbye, Dennis (8 March 2024). "Good News and Bad News for Astronomers' Biggest Dream - The National Science Foundation takes a step (just one) toward an "extremely large telescope."". The New York Times. Archived from the original on 8 March 2024. Retrieved 8 March 2024.
^Jha, Alok (5 August 2006). "Extremely Large Telescope could reveal secrets of life, the universe and everything". The Guardian.
^"Thirty Meter Telescope Construction Proposal" (PDF). TMT Observatory Corporation. 2007-09-12: 29. Archived from the original (PDF) on 2016-03-24. Retrieved 2009-07-24. {{cite journal}}: Cite journal requires |journal= (help)
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of large optical telescopes List of largest infrared telescopes List of largest optical telescopes historically List of largest optical telescopes in...
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mirror substrates for large optical telescopes such as: European Southern Observatory’s Very LargeTelescope and ExtremelyLargeTelescope in Chile, Gran Telescopio...
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learning theory Ending lamination theorem Extremelylargetelescope, a type of telescopeExtremelyLargeTelescope, an astronomical observatory under construction...
be completed by 2024, nearly simultaneously with the 39-meter ExtremelyLargeTelescope being built in Chile; however, on December 2, 2015, the Supreme...
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Inter-American Observatory ExtremelyLargeTelescope La Silla Observatory Llano de Chajnantor Observatory Paranal Observatory Very LargeTelescope List of World Heritage...
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and in understanding the length of the year. Before tools such as the telescope were invented, early study of the stars was conducted using the naked...
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