ESO's Extremely Large Telescope
The world's biggest eye on the sky
Extremely large telescopes are considered worldwide to be one of the highest priorities in ground-based astronomy. They will vastly advance astrophysical knowledge, allowing detailed studies of subjects including planets around other stars, the first objects in the Universe, supermassive black holes, and the nature and distribution of the dark matter and dark energy which dominate the Universe.
Since 2005 ESO has been working with its community and industry to develop an extremely large optical/infrared telescope.
Named the ELT — for Extremely Large Telescope — this revolutionary new ground-based telescope concept will have a 39-metre main mirror and will be the largest optical/near-infrared telescope in the world: “the world’s biggest eye on the sky”.
Astronomy is experiencing a golden era. The past decade alone has brought amazing discoveries that have excited people from all walks of life, from finding planets around Proxima Centauri, the nearest star to the Sun, to the first image of a black hole.
The ELT is a novel ground-based telescope concept with a performance that is orders of magnitude better than currently existing facilities. Equipped with the most advanced instruments, such a telescope may, eventually, revolutionise our perception of the Universe, much as Galileo's telescope did 400 years ago.
The ELT programme was approved in 2012 and green light for construction at Cerro Armazones was given at the end of 2014. The first stone ceremony for the telescope was attended by the President of Chile in May 2017. Dozens of Europe's most cutting-edge companies are participating in the construction. First light is targeted for 2025.
Read more about the ELT
Watch the ESOcast
Download ESOcast 176: Building the Biggest Optical Telescope in the World in the video archive.
For more detailed information, please see our technical pages.
Stars form in dense clouds of the interstellar medium, but even in these densest regions the pressure is comparable to the most tenuous vacuum created in a laboratory on Earth. In these clouds, the temperatures are below -200 degrees Celsius.
The ELT will gather 100 000 000 times more light than the human eye, 8 000 000 times more than Galileo's telescope, and 26 times more than a single VLT Unit Telescope. In fact, the ELT will gather more light than all of the existing 8–10-metre class telescopes on the planet, combined.