ESO’s Extremely Large Telescope halfway to completion

24 August 2023
The ELT’s dome building
Mountain view The ELT’s dome building takes shape in the Chilean Atacama Desert. Credit: ESO

The construction of the world’s largest optical telescope, the Extremely Large Telescope (ELT), has reached its mid-point, stated the European Southern Observatory (ESO) on 11 July. Originally planned to see first light in the early 2020s, operations will now start in 2028 due to delays inherent to building such a large and complex instrument, as well as the COVID-19 pandemic. 

The base and frame of the ELT’s dome structure on Cerro Armazones in the Chilean Atacama Desert have now been set. Meanwhile at European sites, the five-system mirrors for the ELT are being manufactured. More than 70% of the supports and blanks for the main mirror – which at 39 m across will be the biggest primary mirror ever built – are complete, and mirrors two and three are cast and now in the process of being polished.

Along with six laser guiding sources that will act as reference stars, mirrors four and five form part of a sophisticated adaptive-optics system to correct for atmospheric disturbances. The ELT will observe the universe in the near-infrared and visible regions to track down Earth-like exoplanets, investigate faint objects in the solar system and study the first stars and galaxies. It will also explore black holes, the dark universe and test fundamental constants (CERN Courier November/December 2019 p25).

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