The Extremely Large Telescope

The world's biggest eye on the sky

Extremely Large Telescopes are considered worldwide as 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, super-massive 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.

Dubbed 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”.

The ELT programme was approved in 2012 and green light for construction was given at the end of 2014. The first stone ceremony for the telescope was attended by the President of Chile in May 2017.

Science with the ELT

The ELT will tackle the biggest scientific challenges of our time, and aim for a number of notable firsts, including tracking down Earth-like planets around other stars in the "habitable zones" where life could exist — one of the Holy Grails of modern observational astronomy. It will also perform "stellar archaeology" in nearby galaxies, as well as make fundamental contributions to cosmology by measuring the properties of the first stars and galaxies and probing the nature of dark matter and dark energy. On top of this astronomers are also planning for the unexpected — new and unforeseeable questions will surely arise from the new discoveries made with the ELT.

Science goals

General purpose extremely large aperture optical/infrared telescope. Some science areas are to be high redshift galaxies, star formation, exoplanets and protoplanetary systems.

Live image

Follow Cerro Armazones on this live image taken from Cerro Paranal. It is updated every hour during daytime. Click on it to enlarge.

Webcam | 17 May 2017 11:02 CEST

More about the Extremely Large Telescope

ELT Timelapse

View larger timelapse

Watch the ESOcast 84: The New ELT Design Unveiled


Download this trailer in other formats from the Video Archive.


A Tour of Paranal and Cerro Armazones

Virtual Tour of Paranal and Cerro Armazones

Click on the image to take a Virtual Tour at Paranal and nearby Cerro Armazones.



Name: Extremely Large Telescope
Site: Cerro Armazones
Altitude: 3046 m
Enclosure: Hemispherical dome
Type: Optical/near-infrared Giant Segmented Mirror 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
Mount: Alt-Azimuth mount
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?
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.