#39-meter

A New Record Nears: The World's Largest Telescope Prepares For Completion

“The ELT, by the nature of its size, its power, its weight, and its complexity, could never have been a "build-it-and-you're-done" type of telescope. It needs to be continuously adjusted throughout the night to maintain the optimal mirror shape; it needs to be re-calibrated night-to-night to achieve that perfect set point; it needs to have its mirrors recoated every 18 months to keep that ideal 7.5 nanometer smoothness. But if you do all of that, and you use the ideal techniques and instruments — from pointing-and-tracking to adaptive optics to imaging methodology — the ELT has the capability to outclass every other optical telescope ever built, on Earth or in space. It's going to be an incredible technical achievement when complete, an achievement that requires continuous work to maintain. But the science we'll get from it will be unlike anything else our world has ever seen.”

Throughout history, a number of advances have enabled astronomers to collect superior data about the Universe. Smoother mirrors, adaptive optics, superior instrumentation, and optimized photon collection have all made significant contributions, but at some point, you simply have no choice but to go bigger. Doubling the size of your primary mirror doubles your resolution and quadruples your light-gathering power, so bigger is always better. In the mid-2020s, the Extremely Large Telescope (ELT) will be completed, surpassing everything. At 39 meters in diameter, the ELT will be made up of 798 hexagonal segments, each one an impressive 1.4 meters from corner-to-corner. The smoothness of the surface will be a ridiculous 7.5 nanometers, with a resolving power capable of scientific advances the world has never seen. But just as impressive is the technical achievement of making, assembling, and configuring the mirrors. To make the largest, most accurate telescope the world has ever seen means creating something with unprecedented precision.