The Extremely Large Telescope Receives a Steel Framework

 The European Southern Observatory (ESO) has released an image taken atop Chile’s Cerro Armazones, showcasing the progress made in the construction of the Extremely Large Telescope (ELT).

The Largest Observatory on Earth

The ELT will become the largest ground-based observatory conducting research in the optical range. Its central component is a massive 80-meter-high rotating dome weighing 6,100 tons. The diameter of the dome’s enclosure will be 88 meters, which is comparable to the size of a football field.
ELT after completion (concept). Source: ESO

Inside the dome, a 39-meter main mirror will be installed, consisting of 798 individual hexagonal segments with a total surface area of 978 square meters and a weight of 132 tons. It will be dynamically controlled by a high-precision real-time system, ensuring continuous optical alignment. This will enable the observatory to gather 15 times more light than the largest existing optical telescopes.

The ELT’s design also incorporates a fundamentally new adaptive optics technique capable of correcting the distortions caused by Earth’s atmosphere to a high degree of accuracy. It is expected that the new observatory will directly image exoplanets, study their atmospheres, observe the formation of new planetary systems, and contribute to measuring the rate of the universe’s expansion.

The Steel Framework of ELT

As demonstrated in the new image, workers have already begun assembling the steel framework of the ELT’s dome. The components are being assembled at the base camp and then transported to the platform atop Cerro Armazones using special transporters. This is no easy task, considering their weight of approximately 70 tons each. Once in position, the steel blocks, resembling Lego bricks, are lifted by giant cranes and placed on rail-mounted platforms. When operational, the entire dome will rotate on these platforms.
ELT Construction Site. Image taken in June 2023. Source: G. Hüdepohl (

If you look into the distance, to the right of the yellow crane rising behind the structure, you can see another ESO observatory. This is the Very Large Telescope.

The overall budget for the ELT project is estimated at 1.2 billion euros. According to current plans, the telescope is expected to “see the light” in 2028.