ELT

A 39 m primary of 798 hexagonal segments in a five-mirror design with adaptive opticsadaptive opticsCorrecting atmospheric distortion in real time with a deformable mirror driven by a wavefront sensor, at kilohertz rates, using a bright natural star or a laser guide star. Brings large ground telescopes close to their diffraction limit in the infrared. built into the telescope through a 2.4 m deformable fourth mirror. Diffraction-limitedangular resolutionThe smallest angular separation at which two point sources can be told apart. For a filled aperture of diameter D at wavelength λ the diffraction limit is about 1.22 λ/D; for an interferometer, D is the longest baseline. imaging and spectroscopy in the near- and mid-infrared with MICADO, HARMONI and METIS, fed by the MORFEO adaptive optics module, then ANDES and MOSAIC: reflected-light imaging of nearby exoplanets, radial-velocity detection of Earth-massarcsecond1/3600 of a degree (″). A milliarcsecond (mas) is 10⁻³″ and a microarcsecond (µas) 10⁻⁶″. Atmospheric seeing limits ground telescopes to about 0.5–1″ without adaptive optics. planets, the first galaxies and a direct measurement of the cosmic redshiftredshiftz = λ_observed/λ_emitted − 1, the stretching of light by cosmic expansion (or by recession). For distant sources it stands in for distance and look-back time: z ≈ 1 is about 8 Gyr ago, z ≈ 10 about 13.3 Gyr. drift.

Operator

ESO

Site

Cerro Armazones, Chile

Aperture

39 m segmented mirror

Passband

0.4 µm – 13.5 µm

First light

March 2029 (target)