Construction of The Extremely Large Telescope (ELT) in Chile: January 2025 | ESO

Construction of The Extremely Large Telescope (ELT) in Chile: January 2025 | ESO

The European Southern Observatory's Extremely Large Telescope (ELT) is a monumental project. Green light for the construction of the largest optical telescope on Earth started in 2006. As this image, taken in early January 2025 shows, the telescope is nearing its completion, step-by-step. 

The Extremely Large Telescope (ELT) has been appropriately dubbed the "Colosseum of Atacama". This mega-structure is seen in this picture under construction as of early 2025. The evening's sunlight traverses the ELT's dome, illuminating the altitude structure. This 50-meter-tall feat of engineering will carry all 5 mirrors of the ELT, including the giant M1 mirror on its base. The semicircular plate in the image is part of a hydrostatic frame that supports the altitude structure. It is perforated to allow air to flow from the mirror to the ambient air, preventing temperature differences. The ELT is not only a true Colosseum, but everything has been designed in extreme detail. 

This drone shot, dating from early January 2025, peers right into the dome of the Extremely Large Telescope (ELT). The dome is not yet fully covered in this image. Once finished, the ELT will be the world's biggest eye on the sky, thanks to its 39 meter diameter main mirror. It will be supported by the polygon structure inside the dome. The 'spider' on top of it will hold the telescope's secondary mirror at its center.

This image shows the inner frame of the Extremely Large Telescope (ELT), the main structure of the telescope. It will contain all five mirrors of the ELT. Taken in January 2025, the skeleton is completed but still needs to receive all the segments that make up the main 39-meter mirror, set on its honey-comb-shaped base and the other, smaller mirrors. It will be set inside the central tower. Once completed, the ELT will be a leading optical-to-infrared telescope.

The evening sun bathes the construction site of the Extremely Large Telescope (ELT) in red light. This drone image, taken early January 2025, reveals the metal altitude structure inside the dome. It is 50 meters high and will carry the ELT's five mirrors. It rotates so that it can be pointed at different parts of the sky. The 'spider' on top will hold the telescope's secondary mirror, the perforated structure below carries the main mirror, and the central tower supports the ELT's remaining three mirrors.

The European Southern Observatory's Extremely Large Telescope (ELT) is truly a massive building. These images show the construction stage of the ELT's dome and main structure on January 8, 2025. Despite their massive size, these structures are able to rotate and tilt the mirrors to the targeted observation with great precision. The ELT is almost as tall as London's Big Ben clock tower and larger than Rome's Colosseum. The construction materials used for the ELT include: 10,000 tonnes of steel, 30 million bolts or 500 km of cables. Even compared to other large telescopes, the ELT is a one-of-a-kind.

The ELT can be seen including its dome, central structure, and base of the M1 mirror. The ELT stands at Cerro Armazones in Chile's Atacama Desert and will be one of the main flagships of the European Southern Observatory (ESO) for the next two decades. 

Altitude: 3,046 meters

Planned year of technical first light: 2027

Learn more about ESO’s ELT at:

https://elt.eso.org/ 

In 2006, approval was given for the construction of the largest optical telescope on Earth. 

Image Credit: ESO/G. Vecchia

Image Date: Jan. 8, 2025

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