The last hexagonal portion of the primary mirror of the future Extremely Large Telescope (ELT) of the European Southern Observatory (ESO) is ready. It is the largest telescope in the world, an initiative in which Italy is also participating, and whose completion is expected in 2028. The instrument, which will have a final mirror of 39 meters in diameter, will be positioned in Chile in the Atacama desert at 3000 meters above sea level.

The primary mirror is made up of a series of 798 smaller hexagonal mirrors that are about five centimeters thick and 1.5 meters in diameter. A choice that simplifies implementation and at the same time allows correction. The mosaic system allows you to modify the reflective surface and the distortions produced by the atmosphere in real time.

The mirror is made of Zerodur, a low-expansion glass-ceramic material developed by the German company Schott. It is a material designed to resist the extreme temperature variations that can occur in the Atacama desert, a place that allows observation of the sky from a privileged perspective. A step forward for science that promises new discoveries in the cosmos.