Construction of the ELT Dome Foundations Begins

27 September 2019

Construction is now underway of the foundation of ESO’s Extremely Large Telescope (ELT) in the remote Chilean Atacama Desert. Once complete, the telescope will be the largest ground-based telescope in operation, weighing in at 3400 tonnes. The ELT is a reflecting, fully-steerable telescope. The design includes a segmented primary mirror measuring 39.3 metres in diameter, a secondary mirror (4.2 metres in diameter) and a tertiary mirror (3.75 metres in diameter). The telescope will also feature groundbreaking adaptive optics technology that will help correct the distortions in Earth’s atmosphere, making the images sharper than those taken from space. The enclosure itself will be a classic dome shape and will be the telescope’s first defence against the elements. The dome height comes in at nearly 74 metres from the ground and it will span 86 metres in diameter. 

Since the ELT is the largest telescope ever built to date — the question of where to put it was a very tricky one to answer. Locations in Spain, Chile, Morocco and Argentina were tested, and finally, in April 2010, Cerro Armazones in Chile was selected. It was the ideal site thanks to a mixture of different geographical factors which set it above the rest — such as elevation, climate and the very dark skies of the Atacama Desert. The Chilean desert also has very little rainfall (100 mm annually on average), a median wind speed of 25 km/hr and very little water vapour in the air, making it the perfect location for successful astronomy. ESO’s Very Large Telescope (VLT) is only 23 km away meaning a lot of the infrastructure needed to build and maintain the ELT was already in place. 

There are many questions the Universe has yet to answer and the ELT is well equipped to solve these mysteries. One of the ELT’s biggest goals is to find and characterise the atmospheres of rocky exoplanets in habitable zones. The ELT will also study star formation, metal enrichment, the physics of high redshift galaxies, cosmology and fundamental physics. 


Mariya Lyubenova
ESO Head of Media Relations
Garching bei München, Germany
Tel: +49 89 3200 6188

About the Announcement



Construction of the ELT dome foundations begins
Construction of the ELT dome foundations begins
Construction of the ELT dome foundations begins
Construction of the ELT dome foundations begins