ELT secondary mirror blank successfully cast

Opening of the ELT M2 ZERODUR® blank mould containing the still very hot ZERODUR® glass at first annealing at the SCHOTT 4-metre blank annealing facility in Mainz, Germany in May 2017. The completed mirror will be 4.2 metres in diameter and weigh 3.5 tonnes. It will be the largest secondary mirror ever employed on a telescope and also the largest convex mirror ever produced.