The Extremely Large Telescope (ELT) is an astronomical observatory under construction. Part of the European Southern Observatory (ESO) agency, it is located on top of Cerro Armazones in the Atacama Desert of northern Chile. The project was proposed in 2011 with construction beginning in 2017. Completion and first light is anticipated to take place in 2028. The ELT's design consists of a reflecting telescope with a 39.3-metre-diameter (130-foot) segmented primary mirror and a 4.2 m (14 ft) diameter secondary mirror. When completed, it will be the world's largest optical telescope. This picture shows a schematic view of the ELT, released by the ESO in 2012.Design credit: European Southern Observatory