Inside the ELT: the primary mirror

This artist’s animation shows what the inside of ESO’s Extremely Large Telescope (ELT) will look like once its primary mirror is finished. The 39-metre mirror, known as M1, will be by far the largest mirror ever made for an optical telescope. Too large to be made from a single piece of glass, it will consist of 798 glass-ceramic hexagonal segments, each about five centimetres thick and 1.5 metres across. To make sure that all segments can work together as a single mirror, they will be equipped with sensors to detect misalignments. This enormous mirror will allow the telescope to tackle the most profound astronomical challenges of our time, promising groundbreaking discoveries once it sees first light later this decade.