Extremely Large Telescope, under construction the world's largest telescope

ESO's Extremely Large Telescope (ELT) is a revolutionary ground-based telescope that will have a 39-metre main mirror and will be the world's largest telescope for visible and infrared light. 

Construction of this technically complex project is progressing at a good pace, with the ELT being halfway to completion. 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 at a significant pace.

The telescope mirrors and other components are being built by companies in Europe, where work is also proceeding apace. The ESO ELT will have a pioneering five-mirror optical design, including a giant main mirror (M1) composed of 798 hexagonal segments.

The world's largest telescope is halfway through construction
The European Southern Observatory's Extremely Large Earth Telescope (Elt) is a revolutionary project with a 39-metre main mirror that will make it the world's largest telescope for observing visible and infrared light. Construction progress on this technically challenging project is well underway, with the Elt now over 50% complete.
Continuous work
At the moment, engineers and workers are working at a fast pace to assemble the structure of the telescope dome, located atop Cerro Armazones in Chile's Atacama Desert. With daily development, the steel will soon take on the rounded shape typical of telescope domes.
The construction
Construction of the telescope's mirrors and other components is underway at several European companies, and progress is remarkable. The pioneering five-mirror optical design of Eso's Elt includes a huge main mirror (M1) consisting of 798 hexagonal segments. To date, more than 70 per cent of the mirror blanks and holders for these segments have been produced, while the M2 and M3 components have been cast and are currently being polished. Progress with M4, a flexible adaptive mirror that will correct its shape every second to correct distortions caused by atmospheric turbulence, is particularly remarkable: all six thin petals have been completed and are now being integrated into the structure. In addition, all six key resources of Elt's adaptive optics system, the laser sources, have been created and handed over to Eso for verification.
The structure
The ELT is progressing well on all fronts. This includes not only the control system and equipment required for the assembly and operation of the telescope, but also all the other systems required for its completion. In addition to this, the four main scientific instruments that will be integrated into the ELT are at an advanced stage of development, with some about to enter production. Most of the support structure for the ELT is now located in or near Cerro Armazones. For example, the technical building - which will be used, among other things, for the storage and management of the ELT's various mirrors - is fully operational. In addition, a photovoltaic plant that provides clean energy to the site became operational last year.
ESO's new telescope has reached the halfway point of its construction that will lead it to begin observational activities in 2028.
The idea is to start scientific studies in 2028. ESO's Elt will deal with astronomical issues of great importance such as: do we exist alone in the universe? Do the laws of physics apply to the entire universe? How did the first stars and galaxies originate? It will revolutionise our understanding of the universe and lead us to also consider our role in the cosmos.
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