How do you give ESO’s Very Large Telescope an eye exam? Very, very carefully.

Amateur astronomers are familiar with the occasional need to carefully clean their telescope’s optics or, more frequently, to collimate their reflectors. But at the European Southern Observatory in the Atacama desert of Chile, optical maintenance takes on a while new meaning as seen here, as two engineers inspect one of the 8.2-metre (26.9-foot) mirrors making up the Very Large Telescope. While the four telescopes making up the VLT are housed in protective structures, a spring cleaning is required from time to time to prevent the slightest chance of image-altering contamination.

Engineers inspect one of the four 8.2-metre telescopes making up the European Southern Observatory’s Very Large Telescope. Image: G. Hüdepohl (

Along with periodic cleanings, the mirrors must be recoated with a thin layer of aluminium. The ESO video below shows how that delicate process is carried out.