Cerro Armazones is a mountain located in the
Sierra Vicuña Mackenna of the
Chilean Coast Range of
Andes, approximately 130 km (81 mi) south-east of
Antofagasta in the
Antofagasta Region,
Chile. The mountain is located in a privileged zone for
optical astronomy because it has 89% cloudless nights a year.[1] On 26 April 2010, the
European Southern Observatory Council selected Cerro Armazones as the site for the planned
Extremely Large Telescope (ELT); the construction began in June 2014,[2][3] and the first light is expected in 2027.[4] Before the construction of the ELT began, the elevation of Cerro Armazones had been 3,064 metres (10,052 ft),[4][5] but now the top is truncated and the resulting plateau is several meters lower.