ESO's Extremely Large Telescope is now Half Completed

Published: 15 Nov 2023

The European Southern Observatory’s Extremely Large Telescope (ESO’s ELT) will have a 39-metre main mirror and will be the largest telescope in the world for visible and infrared light. Construction of this technically complex project is advancing at a good pace, with the ELT now surpassing the 50% complete milestone.

The telescope is located atop Cerro Armazones in Chile's Atacama Desert, where engineers and construction workers are currently assembling the structure of the telescope dome. The telescope mirrors and other components are being built by companies in Europe, where work is also progressing well. More than 70% of the blanks and supports for the segments of the main mirror have now been manufactured, while two more mirrors, M2 and M3, are cast and in the process of being polished. All six of the thin petals of M4 are fully finalised and being integrated into their structural unit.

All other systems needed to complete the ELT, including the control system and the equipment needed to assemble and commission the telescope, are also progressing well in their development or production. Moreover, all four of the first scientific instruments the ELT will be equipped with are in their final design phase with some about to start manufacturing.

Completing the remaining 50% of the project is anticipated to be significantly quicker than building the first half of the ELT.

At the beginning of October, a time capsule commemorating ESO staff, science, technology and cooperation between ESO and Chile was buried in a ceremony at the construction site of the ELT. The capsule was sealed at the first stone ceremony in 2017, when construction began.

More information is available in the ESO press release about the milestone, and in the ESO Announcement about the time capsule.