Extremely Large Telescope

The Extremely Large Telescope is a 39-meter optical and infrared telescope under construction by the European Southern Observatory on Cerro Armazones in Chile. Its segmented primary mirror is designed to collect far more light and resolve finer detail than existing ground-based telescopes.

Segmented mirror: A large optical surface assembled from multiple smaller mirror segments aligned to act as one reflector. Its 798 hexagonal segments form the ELT’s 39-meter primary mirror.
Exoplanet characterization: The measurement of an exoplanet’s properties, such as its atmosphere, composition, and temperature. ELT instruments are designed to analyze light from exoplanets and their host stars.
Optical telescope: A telescope that collects and focuses visible or near-visible electromagnetic radiation. The ELT is an optical telescope that also extends observations into infrared wavelengths.
European Southern Observatory: An intergovernmental astronomy organization that operates major observatories in Chile. ESO is building and will operate the Extremely Large Telescope.
Adaptive optics: Techniques that correct optical distortions in real time, often by adjusting a deformable mirror. Adaptive optics will counter atmospheric turbulence that would otherwise blur ELT images.
Exoplanet imaging: The direct detection of light from a planet orbiting a star beyond the Solar System. High resolution and adaptive optics can help separate planets from bright host stars.
Infrared astronomy: The study of celestial objects through infrared radiation, whose wavelengths are longer than visible light. Infrared instruments let the ELT study cool objects and distant, redshifted light.
Cerro Armazones: A mountain in Chile’s Atacama Desert selected as the site of the Extremely Large Telescope. The ELT is being constructed on this high, dry observing site.
Laser guide star: An artificial point of light created in the upper atmosphere to provide a reference for adaptive optics. ELT laser guide stars will help measure atmospheric distortions across the sky.
First stars: The earliest generation of stars, formed from nearly pristine hydrogen and helium in the young Universe. The ELT’s light-gathering power is intended to probe very faint early-universe objects.

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