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ESO's Extremely Large Telescope

The world's biggest eye on the sky

Highlights

Artist’s rendering of the ELT in operation

ESO signs largest ever ground-based astronomy contract for E-ELT dome and telescope structure

Artist's rendering of the Extremely Large Telescope

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.

Press releases

First ELT Main Mirror Segments Successfully Cast

ESO Signs Contracts for the ELT’s Gigantic Primary Mirror

First Stone Ceremony for ESO's Extremely Large Telescope

Secondary Mirror of ELT Successfully Cast

Contracts Signed for ELT Mirrors and Sensors

Find here the latest ELT Announcements and Press releases.

The ELT Project is hiring. Check the ESO job portal.

Watch the ESOcast

Download ESOcast 176: Building the Biggest Optical Telescope in the World in the video archive.

ELT

For more detailed information, please see our technical pages.

Name:	Extremely Large Telescope
Site:	Cerro Armazones
Altitude:	3046 m
Enclosure:	Hemispherical dome
Type:	Optical/near-infrared extremely large telescope
Optical design:	Five-mirror design — three-mirror on-axis anastigmat + two fold mirrors used for adaptive optics
Diameter. Primary M1:	39 m (798 hexagonal 1.4 m mirror segments)
Material. Primary M1:	Zerodur®
Diameter. Secondary M2:	4 m
Material. Secondary M2:	Zerodur®
Diameter. Tertiary M3:	3.75 m
Diameter. M4:	2.4 m
Diameter. M5:	2.7 x 2.1 metres
Mount:	Alt-Azimuth mount
First Light date:	2025
Active Optics:	Yes
Adaptive Optics:	2.60 m adaptive M4 using 6 Laser Guide Stars
Images taken with the ELT:	Link
Images of the ELT:	Link
Videos of the ELT:	Link
Press Releases with the ELT:	Link

Did you know?
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.