Finding a home
An extraordinary telescope calls for an exceptional site. Much care is thus taken to ensure that the future home of the ELT will be the most adequate possible. This generally means a high, dry site, so as to have as little hindrance to the observations. The ELT Site Selection Advisory Committee has been investigating in great detail several possible sites, in Argentina, in Chile, in Morocco, and in Spain. Similar efforts are being carried out by the Thirty-Meter Telescope (TMT) site selection team. For the sake of efficiency, the TMT pre-selected sites (all in North and South America) are not included in the ELT study, but data are shared.
On 2–3 March 2010, the ELT Site Selection Advisory Committee presented a report to the ESO Council, confirming that all sites examined in the final short list (Armazones, Ventarrones, Tolonchar and Vizcachas in Chile, and La Palma in Spain) have very good conditions for astronomical observing, each one with its particular strengths. The technical report concludes that Cerro Armazones, near Paranal, stands out as the clearly preferred site, because it has the best balance of sky quality across all aspects and it can be operated in an integrated fashion with the existing ESO Paranal Observatory.
Cerro Armazones is a mountain at an altitude of 3060 metres in the central part of Chiles Atacama Desert, some 130 kilometres south of the town of Antofagasta and about 20 kilometres from Cerro Paranal, home of ESO's Very Large Telescope.
On 26 April 2010, the ESO Council selected Cerro Armazones as the baseline site for the planned 39-metre-class Extremely Large Telescope (ELT).
On 13 October 2011, an agreement was signed between ESO and the Chilean government, including the donation of 189 km2 of land around Cerro Armazones for the installation of the ELT as well as a concession for 50 years relating to the surrounding area.
On 27 October 2013, the President of Chile, Sebastián Piñera, handed over the signed legal documents by which the Chilean government transferred this land around Cerro Armazones to ESO.