Technology
A Look at the World’s Largest Infrared Light Telescope
By Matt De Vlieger · December 23, 2023
Five-Mirrror Design
The European Southern Observatory's (ESO) Extremely Large Telescope (ELT) in Chile is set to become the world’s largest eye on the sky in the next decade. It will tackle significant scientific challenges and pursue several groundbreaking achievements, including the search for Earth-like planets in the "habitable zones" of other stars, a major goal in modern observational astronomy.The telescope's design is groundbreaking, featuring a unique five-mirror scheme that ensures exceptional image quality. Its primary mirror comprises nearly 800 segments, each 1.4 meters wide but only 50 mm thick. Additionally, the optical design includes a massive secondary mirror measuring 4.2 meters in diameter, surpassing the primary mirrors of any of ESO's telescopes at La Silla.
To counteract the blurring effects caused by atmospheric turbulence, adaptive mirrors are integrated into the telescope's optics. One of these mirrors is supported by over 6000 actuators capable of altering its shape a thousand times per second.Equipped with multiple scientific instruments, the ELT will have the capability to swiftly switch between them, allowing for seamless transitions within minutes. Furthermore, both the telescope and its dome will have the ability to rapidly reposition themselves in the sky and commence new observations in a short timeframe. L. Calçada/ESO
First Mirrors Heading to Chile
In an unprecedented step toward unlocking the secrets of the cosmos, the first 18 hexagonal mirror segments destined for the Extremely Large Telescope have have begun their 6,700 mile journey from France to the construction site atop Cerro Armazones in the arid deserts of northern Chile. This marks a significant milestone in the ambitious project, which began construction in 2014. Credit: A. Centeio/ESO
That's a BIG Mirror
The main mirror, M1, is too immense to be physically fabricated as a single mirror, and will instead be constructed from 798 individual segments, each segment aproximately 1.4m in diameter and just 5cm thick. These segments form an expansive hexagonal pattern, and an extra 133 are being manufactured to facilitate the periodic recoating of the mirror. Boasting a diameter exceeding 39 meters, M1 is destined to become the largest telescope mirror in the world. The picture above shows a full-sized mock-up of the M1 mirror built by participants at ESO's Open House Day 2011. ESO
Polishing the Mirrors
Prior to their delivery, the mirror segments underwent meticulous refinement by Safran Reosc, a French optical systems manufacturer. Utilizing a technique known as 'sweeping,' the mirrors' imperfections were atomically polished out by exposing their surfaces to a precise beam of ions that selectively erode irregularities. As a result of this meticulous process, any residual flaws are now confined to dimensions no larger than 10 nanometres, akin to the scale of a biological cell membrane. As of November 1, 2023, the 100th segment completed its production journey, transitioning to the thorough inspection phase that precedes its final delivery. In the upcoming months, Safran Reosc will continue the polishing and shipment of the remaining 780 pieces of M1. Safran
Mirror Size Comparison
This infographic has been created to compare the size of the main mirror of the European Extremely Large Telescope (E-ELT) with that of other significant ground-based telescopes, whether currently in operation or planned. The infographic was inspired by the work of Wikipedia author Cmglee. ESO