A giant mirror goes back to work

The 8.2-metre primary mirror (M1) of one of the VLT’s four giant telescopes is being transported from the Main Maintenance Building (MMB) back to its telescope, after a recoating. This delicate operation is carried out every 18 months. Since the telescopes spend the night under the stars, a certain amount of dirt accumulates on the surface of the mirrors, reducing their reflectivity and diminishing the quality of the astronomical image. During the cleaning process, the existing aluminium layer is removed and the mirror is recoated. This photograph is slightly blurry because of the effect of the atmospheric turbulence near the ground in the daytime. In spite of this, the atmosphere above Paranal is characterised by an extremely low turbulence and a great stability. These characteristics make the Paranal area one of the world’s best sites for ground-based optical astronomy.