European
Southern
Observatory

About | Facts about the ELT
Name

Extremely Large Telescope (ELT)

Main mirror diameter

39 metres

Light collecting area

978 square metres

Number of main mirror segments

798

Alignment precision of the different segments that make up the main mirror

Tens of nanometres (10000 thinner than a human hair) across its entire 39-metre diameter

 

Number of edge sensors that will measure the relative positions of the segments

4608

Amount of glass-ceramic Zerodur(c) in the telescope mirrors

140 tonnes, of which 132 tonnes in the primary mirror alone

How much light will the ELT gather?
Type

Optical/near-infrared extremely large telescope

Optical Design

Five-mirror design

Telescope field of view

10 arcminutes

Enclosure

Hemispherical Dome

Time needed to walk from the entrance of the dome to the top via the set of stairs and walkways fixed to the inner side of the dome

~30 minutes

Site

Cerro Armazones, Atacama Desert, Chile

Altitude

3046 m

Height of rock removed from the top of Armazones to create the platform for the ELT

~18 metres

Amount of rock removed to make room for the 150 metre by 300 metre ELT platform

~220 000 m3

Distance between Armazones and Paranal (by air)

23 km

Planned duration of the telescope construction

About 12 years

Planned year of technical first light

2025

Estimated lifespan

30+ years

Budget

€1.3 billion

Number of industrial contracts above €500 000 made to date

~43

Number of ESO staff (Full-Time Equivalent) the ELT uses on average during 2018–2022

~100 each year