A reflection on an M1 mirror segment

Two ESO engineers at Paranal Observatory, Chile, including Optical Coating Engineer Ricardo Parra at the centre, check over a newly coated mirror segment of the Extremely Large Telescope (ELT), demonstrating just how reflective it is. Engineers are able to get this incredible reflectivity using 1.7g of silver spread across the segment’s surface. The process of integrating electricals into and coating these segments takes a lengthy 6-7 hours (even applying the coating itself takes up to 2 hours), and they are then checked thoroughly before being returned to storage.