Primary mirror
128 ft
A segmented primary with 798 hexagonal mirror segments.
Observatory Watch · ESO
Extremely Large Telescope
ESO’s ELT is a 128-foot optical and near-infrared observatory under construction on Cerro Armazones in Chile. StarStation tracks the engineering, instruments, science goals, and the road to technical first light.
Current status
Under construction
Technical first light
2029 target
Site
Cerro Armazones
The 2029 date is ESO’s planned year for telescope test observations. ESO targets telescope first light in March 2029 and scientific first light in December 2030. Both dates are provisional; see the official ESO timeline below.
Light-collecting area
10,527 sq ft
ESO’s published collecting area for the ELT primary system.
Optical design
5 mirrors
A five-mirror system with adaptive optics built into the telescope architecture.
Elevation
9,993 ft
High in Chile’s Atacama Desert, near ESO’s Paranal Observatory.
Official roadmap
What has to happen before first science.
ESO's current ELT timeline separates construction milestones from telescope first light and later scientific operations. These are planned dates, not guaranteed deadlines.
2026 verified milestones
In an ESO image release dated 27 April 2026, the ELT was described as more than 70% complete. That figure is a dated construction snapshot, not a live progress meter. In July 2026, ESO documented the first rotation of the 7.7-million-pound telescope structure, a major test of its ability to point across the southern sky. These engineering tests do not mean the telescope has reached first light.
2026
M2 complete
ESO lists completion of the 13.9-foot secondary mirror, the largest convex mirror made for a telescope, as a 2026 project milestone.
2027
Dome + structure + M3
ESO plans completion of the dome, main telescope structure, and 12.3-foot tertiary mirror.
2028
M1 + M4 + M5
Installation of all 798 primary-mirror segments is planned to finish, alongside completion milestones for the adaptive M4 unit and fast tip-tilt M5 mirror.
Mar 2029
Telescope first light
ESO plans telescope first light after initial test observations and major system integration.
Dec 2030
Scientific first light
ESO expects the first observations delivered with scientific instruments after installation and commissioning.
How the light moves
Five mirrors, each with a different job.
The ELT does more than collect a huge amount of light. Its optical train actively corrects and stabilizes that light before it reaches the science instruments.
M1
Collect
128-foot segmented primary mirror. It gathers the incoming light and sends it toward M2.
M2
Reflect
A giant convex secondary mirror redirects the light toward the tertiary mirror.
M3
Relay
The tertiary mirror relays the beam toward the adaptive-optics mirrors.
M4
Correct
A deformable mirror changes shape rapidly to correct atmospheric turbulence and residual optical errors.
M5
Stabilize
A fast tip-tilt mirror stabilizes the image before the light reaches the instruments.
First-generation instruments
The telescope is only half the story.
Once the ELT’s optics collect and correct the light, its instruments turn that light into images and spectra. ESO's first-generation suite is HARMONI, MICADO, MORFEO, and METIS. ANDES and MOSAIC are planned to begin operations later.
3D spectroscopy
HARMONI
Visible and near-infrared integral-field spectroscopy for distant galaxies, stars, black holes, and exoplanets.
High-resolution imaging
MICADO
A near-infrared camera designed for extremely sharp and deep imaging.
Adaptive-optics relay
MORFEO
A multiconjugate adaptive-optics system that will help MICADO achieve exceptional image quality.
Mid-infrared imaging + spectroscopy
METIS
A high-contrast infrared imager and spectrograph for planets, disks, stars, and distant objects.
High-resolution spectroscopy
ANDES
A later-stage high-resolution spectrograph aimed at extremely sensitive measurements.
Multi-object spectroscopy
MOSAIC
A later-stage instrument designed to measure many stars and galaxies efficiently.
Why astronomers are building it
The science cases reach from nearby planets to the early Universe.
Exoplanets
Characterize other worlds.
ESO lists direct imaging and atmospheric characterization of exoplanets, including worlds in habitable zones, among the ELT’s highest science priorities.
Black holes
Probe extreme gravity.
The ELT is designed to study the Milky Way’s central black hole and black holes in other galaxies with unprecedented detail.
Galaxies
Resolve the distant Universe.
Its collecting power and angular resolution will let astronomers study distant galaxies and their internal structure across cosmic time.
Fundamental physics
Test cosmology.
ESO includes dark matter, dark energy, stellar evolution, and other fundamental questions in the ELT science case.
What to watch next
The road to first light is itself a major astronomy story.
StarStation will treat ELT development like an observatory mission timeline: major structure milestones, mirror progress, instrument integration, commissioning, and eventually first-light results.
01
Structure + dome
Track major construction and enclosure milestones on Cerro Armazones.
02
Primary mirror system
Watch segment production, coating, installation, alignment, and active-control progress.
03
Adaptive optics
Follow M4/M5 integration and the systems required to correct atmospheric turbulence.
04
First instruments
Watch HARMONI, MICADO, MORFEO, and METIS move from integration toward commissioning.
05
Technical first light
ESO targets March 2029 for initial telescope test observations, before instrument commissioning.
06
Science verification
ESO targets scientific first light in December 2030, followed by verification that the instruments deliver their intended performance.
StarStation source standard
Primary-source facts first.
Engineering figures, instrument status, and schedule language on this page are based on ESO’s ELT project materials. StarStation will not convert a target year into a fake exact countdown or imply that future instruments are already operational.