Through the looking glass
This picture shows the ‘raw’ glass that will eventually form one of the mirrors for the Giant Magellan Telescope (GMT) at Chile’s Las Campanas Observatory.
Due to commence stargazing operations in 2025, the finished ’scope will have seven 8.4m mirrors that combine to give it an effective aperture of 24.5m. This enables the GMT to produce infrared images that are 10 times sharper than those captured by the Hubble Space Telescope.
That level of optical precision can only be achieved through the use of high-quality materials and an exacting production process. Here, blocks of low-expansion E6 glass made by Japan’s Ohara Corporation, weighing a total of 17,481kg, have been placed inside a hexagonal mould and are about to be heated to 1,165°C in a giant furnace that spins at 5rpm.
The glass will take around four hours to melt and settle into the mould, after which the furnace will rotate more slowly as the glass is carefully cooled over the course of three months.
Once this stage is complete, the mirror will be ready for shaping and polishing.