Atop the mountain Cerro Armazones in Chile, construction is underway on the Extremely Large Telescope (ELT), which will usher in a new era of astronomy when it's completed. The ELT will be the world's largest telescope, with a primary mirror that measures 128 feet (39 meters) across.

What is it?

Astronomy depends as much on location as it does on technology. To observe the faintest and most distant objects in the universe, telescopes need dark, dry and stable skies, conditions that are increasingly rare on Earth. Mountains in the Chilean Atacama Desert, like Cerro Armazones, offer an almost perfect natural laboratory. Situated at high altitude, far from cities, and in one of the driest places on the planet, they provide exceptionally clear nights with minimal atmospheric disturbance.

For more than six decades, this environment has made Chile the global center of ground-based astronomy. The European Southern Observatory (ESO) operates all of its observatories here, including the Very Large Telescope (VLT) at Cerro Paranal and, soon, the ELT. Together, these facilities represent humanity's ongoing effort to understand the cosmos, from nearby exoplanets to the earliest galaxies.

Where is it?

The ELT is under construction atop Cerro Armazones, which is a mountain in Chile's Atacama Desert.

Why is it amazing?

Scientifically, the ELT represents a transformative leap. With its massive mirror and advanced instruments, it will be able to directly image exoplanets, analyze their atmospheres for signs of habitability, study the formation of stars and galaxies, and probe the nature of dark matter and dark energy. The proximity of ELT and VLT reflects continuity in scientific progress, with each new generation of telescopes building upon the legacy of the last.

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You can learn more about the Extremely Large Telescope and other ground-based telescopes.

High up in the Chilean Andes, the Extremely Large Telescope (ELT) is set to become the world's largest optical telescope and one of the most ambitious scientific instruments ever built. Developed by the European Southern Observatory, the ELT represents a major leap forward in humanity's ability to study the universe with unprecedented clarity.

What is it?

Construction on the ELT officially began in 2014, with the observatory designed around a segmented primary mirror that's 128 feet (39 meters) wide — nearly five times larger than any current ground-based optical telescope mirror. Once operational, the ELT will use advanced adaptive optics to correct for atmospheric turbulence, yielding images 15 times sharper than those from the Hubble Space Telescope.

Where is it?

This drone image was taken high above Cerro Armazones, the 9,993 -oot-tall (3,046 m) mountain where the ELT is located.

Why is it amazing?

Given its advanced instruments, the ELT's overarching mission is to push observational astronomy into a new precision era. The huge telescope will directly image small, rocky exoplanets and look for possible conditions suitable for life outside our solar system. The ELT will also help scientists study our universe's origins by looking at distant galaxies while also measuring the universe's rate of expansion. This telescope will also be used to study stellar dynamics and how stars are born, evolve and sometimes turn into black holes.

As the ELT's construction nears completion, the world waits to see just what this cutting-edge telescope will show us about the world we live in.

Want to learn more?

You can learn more about the Extremely Large Telescope and other ground-based telescopes.

Deep in the Chilean desert, the European Extremely Large Telescope (ELT) is currently under construction. Operated by the European Southern Observatory (ESO), the ELT's design features a 128-foot-wide (39 meters) primary mirror, making it the largest optical and infrared telescope in the world when completed.

In this image, cranes flank the rising solar disk with Earth still in shadow as the first light silhouettes humanity’s next giant eye on the sky.

What is it?

The ELT is one of the most ambitious ongoing projects in astronomy, with a cost of 1.3 billion euros (around $1.4 billion US). Construction is underway atop Cerro Armazones, a mountaintop in Chile's Atacama Desert. Here, the lack of light pollution and moisture will allow the telescope to take more accurate readings of deep space and its structures.

Where is it?

This photograph was taken at Cerro Armazones in Chile, at an elevation of 10,052 feet (3,064 m) above sea level.

Why is it amazing?

The ELT’s size and advanced instrumentation will let astronomers see fainter and more distant objects than ever before. The giant scope will image exoplanets in reflected light, explore the earliest galaxies formed after the Big Bang and much more.

As the sun rises behind the ELT, the image stands for the dawning of a new era in astronomical discovery. When operational, the ELT will help us observe light from the most ancient parts of the universe.

Want to learn more?

You can read more about astronomy and telescopes in Chile.

In the middle of Chile's Atacama desert, there's lots of activity as construction on the Extremely Large Telescope (ELT) is still underway, with cranes helping to move pieces in place.

What is it?

The ELT is the European Southern Observatory's (ESO) $1.4 billion project to create the next-generation observatory.

Here, the world's largest optical telescope will scan the sky with a primary segmented mirror stretching 128 feet (39 meters) in diameter, roughly four times larger than any current ground-based optical telescope. The large mirror will not only allow the telescope to collect more light, but according to the ESO, the telescope will also provide images 15 times sharper than the Hubble Space Telescope.

Where is it?

The ELT is being built in Chile's Cerro Armazones, a mountaintop in the Atacama desert.

Why is it amazing?

In April 2025, crews at the ELT celebrated the telescope's topping-out or roofing ceremony, as the roof was raised over the dome of the telescope. Flags from both the ESO and Chile were placed on the scaffolding over the roof.

In Chilean tradition, this ceremony is known as Tijerales, and was celebrated on April 16, 2025 with a traditional barbeque for the crew. The ceremony was also livestreamed to ESO's headquarters in Garching, Germany, bringing together an international community excited about the future of astronomy.

Want to learn more?

You can read more about the Extremely Large Telescope and other telescopes in Chile.

The world's largest telescope has gotten its official construction go-ahead, keeping the enormous instrument on track to start observing the heavens in 2024.

The European Extremely Large Telescope (E-ELT), which will feature a light-collecting surface 128 feet (39 meters) wide, has been greenlit for construction atop Cerro Armazones in Chile's Atacama Desert, officials with the European Southern Observatory (ESO) announced Thursday (Dec. 4).

"The decision taken by Council [ESO's chief governing body] means that the telescope can now be built, and that major industrial construction work for the E-ELT is now funded and can proceed according to plan," Tim de Zeeuw, ESO's director general, said in a statement. "There is already a lot of progress in Chile on the summit of Armazones, and the next few years will be very exciting." [Photos: World's Largest Telescope Being Built in Chile]

E-ELT construction was first approved in June 2012, but on the condition that contracts worth more than 2 million euros ($2.48 million at current exchange rates) could be awarded only after 90 percent of the total funding required to build the telescope (1.083 billion euros, or $1.34 billion, at 2012 prices) had been secured. An exception was made for "civil works," including the leveling of the site and a road up Cerro Armazones, ESO officials said.

The 90-percent threshold was reached in October, when Poland agreed to join ESO, officials said, but making the numbers work took some tweaking. ESO split E-ELT development into two phases: 90 percent of the project's costs go toward "Phase 1," which will get E-ELT up and running, and 10 percent of the costs are allocated to "Phase 2," for the development of nonessential elements. These include about one-quarter of E-ELT's 798 individual mirror segments (which together make up the huge main mirror) and part of the telescope's adaptive optics system, which helps cancel out the blurring effects of Earth's atmosphere.

The current construction approval applies only to Phase 1; contracts for this work will be awarded in late 2015. The Phase 2 components will be approved as more funding becomes available, ESO officials said.

"The funds that are now committed will allow the construction of a fully working E-ELT that will be the most powerful of all the extremely large telescope projects currently planned, with superior light-collecting area and instrumentation," de Zeeuw said. "It will allow the initial characterization of Earth-mass exoplanets, the study of the resolved stellar populations in nearby galaxies as well as ultra-sensitive observations of the deep universe."

As de Zeeuw said, E-ELT is not the only giant ground-based telescope in the works. The Giant Magellan Telescope (GMT) will soon start taking shape atop Las Campanas, another Chilean peak. GMT will arrange seven 27.6-foot-wide (8.4 m) primary mirrors into one light-collecting surface 80 feet (24 m) across; project officials are aiming for "first light" in 2021.

And the Thirty Meter Telescope (TMT) — which, not surprisingly, will boast a light-collecting surface 30 m, or 98 feet, wide — is slated to start observing from Hawaii's Mauna Kea in 2022. Like E-ELT, TMT's primary mirror will be composed of hundreds of relatively small segments.

All three megascopes should help researchers tackle some of the biggest questions in astronomy, including the nature of the mysterious dark matter and dark energy that make up most of the universe.

Follow Mike Wall on Twitter @michaeldwall and Google+. Follow us @Spacedotcom, Facebook or Google+. Originally published on Space.com.