A giant under the moonlight

It’s now close to 80 metres high — the mammoth steel structure of the ESO’s Extremely Large Telescope (ELT) dome is taking shape in this Picture of the Week, taken on 2 August 2023 under the light of the full Moon. Right now, engineers and construction workers are assembling the structure of the telescope dome in the Chilean Atacama Desert, with progress visible almost every day. When completed, the ELT will be the world’s biggest eye on the sky for visible and infrared observations. 

Overall, the ELT project is now more than 50 percent complete. The dome structure visible here will house a pioneering five-mirror optical design, which includes a giant main mirror (M1), 39 metres wide and made up of 798 hexagonal segments. The telescope mirrors and other components are being built by companies in Europe, where work is progressing well too. All of the other systems needed to complete the ELT, including the control system and the equipment needed to assemble and test the telescope, are also coming along nicely.

When finished, the dome will weigh in at 6100 tonnes, and it will need a mind-boggling 30 million bolts to be held together. This huge structure will shelter the telescope during observations, protecting it from the elements. The entire behemoth will rotate on 36 stationary trolleys, allowing astronomers to observe the southern sky from just about any direction they fancy.