page_title: Extremely Large Telescope
section_title: History
hierarchical_section_title: Extremely Large Telescope / History
caption_attribution_description: English: This picture was taken at ESO’s Garching Headquarters during the historic Council meeting of 11–12 June 2012 when the E-ELT programme was approved (subject to confirmation of the so-called ad referendum votes). For a glimpse back in time compare with the photo at the Council approval of the VLT in December 1987.
context_page_description: The Extremely Large Telescope is an astronomical observatory currently under construction. When completed, it is planned to be the world's largest optical/near-infrared extremely large telescope. Part of the European Southern Observatory agency, it is located on top of Cerro Armazones in the Atacama Desert of northern Chile. The design consists of a reflecting telescope with a 39.3-metre-diameter segmented primary mirror and a 4.2 m diameter secondary mirror, and will be supported by adaptive optics, eight laser guide star units and multiple large science instruments. The observatory aims to gather 100 million times more light than the human eye, 13 times more light than the largest optical telescopes existing in 2014, and be able to correct for atmospheric distortion. It has around 256 times the light gathering area of the Hubble Space Telescope and, according to the ELT's specifications, would provide images 16 times sharper than those from Hubble. The project was originally called the European Extremely Large Telescope, but the name was shortened in 2017.
context_section_description: On 26 April 2010, the European Southern Observatory (ESO) Council selected Cerro Armazones, Chile, as the baseline site for the planned ELT. Other sites that were under discussion included Cerro Macon, Salta, in Argentina; Roque de los Muchachos Observatory, on the Canary Islands; and sites in North Africa, Morocco, and Antarctica.
  Early designs included a segmented primary mirror with a diameter of 42 metres (140 feet) and an area of about 1,300 m² (14,000 sq ft), with a secondary mirror with a diameter of 5.9 m (19 ft). However, in 2011 a proposal was put forward to reduce its size by 13% to 978 m², for a 39.3 m (130 ft) diameter primary mirror and a 4.2 m (14 ft) diameter secondary mirror. It reduced projected costs from 1.275 billion to 1.055 billion euros and should allow the telescope to be finished sooner.  The smaller secondary is a particularly important change; 4.2 m (14 ft) places it within the capabilities of multiple manufacturers, and the lighter mirror unit avoids the need for high-strength materials in the secondary mirror support spider.
  ESO's Director General commented in a 2011 press release that "With the new E-ELT design we can still satisfy the bold science goals and also ensure that the construction can be completed in only 10–11 years." The ESO Council endorsed the revised baseline design in June 2011 and expected a construction proposal for approval in December 2011. Funding was subsequently included in the 2012 budget for initial work to begin in early 2012. The project received preliminary approval in June 2012. ESO approved the start of construction in December 2014, with over 90% funding of the nominal budget secured.
  The design phase of the 5-mirror anastigmat was fully funded within the ESO budget. With the 2011 changes in the baseline design (such as a reduction in the size of the primary mirror from 42 m to 39.3 m), in 2017 the construction cost was estimated to be €1.15 billion (including first generation instruments). As of 2014, the start of operations was planned for 2024. Actual construction officially began in early 2017.
caption: ESO Council meets at ESO headquarters in Garching, 2012.[11]
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