World’s largest telescope gets its protective shell (photos)
Construction has reached a pivotal stage for the dome that will house the world’s largest telescope, marking a significant milestone in the development of this groundbreaking observatory. The European Southern Observatory’s (ESO) Extremely Large Telescope (ELT), set to become the world’s largest visible- and infrared-light telescope, is taking shape on Cerro Armazones mountain in Chile’s Atacama Desert. The dome, a marvel of engineering, is now two-thirds complete, with its massive steel skeleton visible against the stark desert backdrop. Weighing approximately 6,100 metric tons, the dome will eventually stand at 262 feet (80 meters) tall and span 289 feet (88 meters) in diameter. Its construction at such a remote and challenging location, 9,993 feet (3,046 meters) above sea level, highlights the monumental effort behind this project.
Inside the dome, work progresses on the polygon structure supporting the telescope’s main mirror (M1) and the “spider” structure positioned above it, which will hold the secondary mirror (M2) in place. M1, an impressive 128 feet (39 meters) across, will consist of 798 hexagonal segments, each roughly 2 inches (5 centimeters) thick and 5 feet (1.5 meters) wide. These segments, made of glass ceramic, will form the largest mirror ever constructed for an optical telescope. Meanwhile, the spider structure, nearing completion, will support M2, which measures 14 feet (4.25 meters) in diameter. When finished, the ELT will feature a total of five mirrors, though only two are currently underway.
Below the spider structure, the central tower is taking shape to support the telescope’s remaining three mirrors. These components — the central tower, spider structure, and polygon base — are mounted on the altitude structure. This 164-foot (50-meter) metal frame will carry all five mirrors and rotate to allow the telescope to point at different areas of the sky. Together, these elements form the heart of the ELT, designed to revolutionize our understanding of the universe. From studying exoplanets to exploring the early universe, the telescope will open new frontiers in astronomy.
The ELT’s construction, led by a consortium including the Italian company Cimolai, showcases collaborative international effort and cutting-edge engineering. With its advanced adaptive optics system, the telescope will compensate for atmospheric turbulence, delivering images 16 times sharper than those from the Hubble Space Telescope. Scheduled to achieve its first light in 2028, the ELT promises to unveil cosmic mysteries with unparalleled clarity, cementing its place as a cornerstone of astronomical discovery.