Construction of the world’s largest visible- and infrared-light telescope, the Extremely Large Telescope (ELT), is steadily advancing in the Atacama Desert of Chile, Space.com reports.
Recent updates from the European Southern Observatory (ESO) highlight progress on key components of the telescope’s structure, including its massive dome, central support structure, and the base for its primary mirror. Once operational, the ELT will provide an unprecedented view of the cosmos, enabling groundbreaking observations of exoplanets, distant galaxies, and the expansion of the universe.
Located atop the Cerro Armazones mountain, the ELT is designed to be the most powerful ground-based optical telescope in the world. Its “first light” — the moment it will make its first observations — is scheduled for 2028. Once fully operational, it will become one of the primary instruments of the European Southern Observatory for at least the next two decades.
The ELT’s massive size is central to its mission. Its main mirror, known as the M1, will be a 128-foot (39-meter) colossus composed of 798 individual hexagonal segments. This mirror alone will weigh 200 tons and be supported by a large white lattice structure within the central dome. This structure allows the mirror to adjust its position during observations to compensate for factors such as wind, vibrations, and shifts in temperature.
The observatory’s five-mirror system will enable the ELT to capture light with unmatched precision and clarity. The primary M1 mirror will reflect light to a 14-foot (4.25-meter) convex mirror (M2) — the largest convex mirror ever built — before passing it to the 12-foot (3.75-meter) M3 mirror. Two additional mirrors (M4 and M5) will further correct distortions caused by atmospheric turbulence, ensuring crystal-clear images of the universe.
The ESO recently released photos and videos documenting significant construction progress at the site. The images showcase the steady development of the ELT’s dome, central structure, and mirror base. The construction timeline indicates that the M2 mirror will be completed by 2025, while the dome and telescope structure are set for completion in 2026. The M3 mirror is expected to be ready by 2027.
Construction updates are available to the public through interactive webcam footage and time-lapse videos, offering a real-time look at the progress on Cerro Armazones. Drone footage shows the site illuminated by the glow of the rising sun, emphasizing the scale and ambition of the project.
The observatory’s dome, which will house the telescope, is being built to shield the sensitive instruments from weather and temperature fluctuations while still allowing for smooth, unobstructed observations of the night sky.
Once operational, the ELT will be a game-changer for astronomy. With its enormous mirror system and advanced adaptive optics, the telescope will offer views of the universe with far greater clarity than current ground-based observatories. Its primary mission is to detect and study Earth-like exoplanets and analyze their atmospheres for signs of habitability or potential life.
The telescope will also investigate some of the universe’s biggest mysteries, such as the nature of dark matter and dark energy, by measuring the universe’s expansion rate. Its massive size and sophisticated mirror system will allow astronomers to collect more light and achieve sharper images than any other ground-based optical telescope in history.
The ELT is a testament to human ingenuity and international collaboration. By the time it captures its first light in 2028, it will be one of the most significant technological achievements in modern astronomy. As construction progresses, updates will continue to be shared through the ESO’s interactive webcams, drone footage, and photographic updates.
