Free Astronomy Magazine March-April 2018

48 MARCH-APRIL 2018 SPACE CHRONICLES much too large to be made from a single piece of glass, so it will consist of 798 individual hexagonal seg- ments, each measuring 1.4 metres across and about 5 centimetres thick. The segments will work together as a single huge mirror to collect tens of millions of times as much light as the human eye. Marc Cayrel, head of ELT optomechanics at ESO, was pre- First ELT main mirror segments successfully cast by ESO T he 39-metre-diameter primary mirror of ESO’s Extremely Large Telescope will be by far the largest ever made for an optical- infrared telescope. Such a giant is T he first hexagonal segments for the main mirror of ESO’s Extremely Large Telescope (ELT) are shown being success- fully cast by the German company SCHOTT at their facility in Mainz. These segments will form parts of the ELT’s 39- metre main mirror, which will have 798 segments in total when completed. The ELT will be the largest optical telescope in the world when it sees first light in 2024. [SCHOTT/ESO]