Eighteen giant telescope mirrors destined for the Extremely Large Telescope (ELT) of the European Southern Observatory (ESO) have arrived in Chile just in time for Christmas. These mirrors are just a fraction of the 798 hexagonal pieces that will be assembled to create the mirror, making it the largest in the world in the category of optical and infrared telescopes. The ELT’s mission is to begin capturing light from alien worlds, ancient galaxies, and supermassive black holes in 2028.
Each of the segments that make up the ELT mirror has dimensions of around 1.4 meters wide and a thickness of less than 0.7 cm. The precision required for their shape is within fractions of the wavelength of light. The segments made a long journey from a manufacturing facility in Germany where the glass was melted, to a facility in France where they were polished using a microscopic ion beam.
The segments are being stored in a special bag and transported in temperature-controlled containers, equipped with special air cushions and nitrogen to prevent deformation of the thin sheets of glass. Once in Chile, the mirror segments must receive an extremely thin coating of silver, just 150 nanometers thick, using magnetron sputtering.
Once assembled, the 798 glass and silver hexagons will create the ELT’s primary mirror, capturing light from distant objects and redirecting it towards instruments intended to help astronomers interpret images. The ELT is scheduled to begin operations in 2028.