The Exciting Little Timelapse: A year in the life of the ELT

Last year saw outstanding progress for ESO’s Extremely Large Telescope (ELT). In this Picture of the Week, we’re looking back in time to see just how far the ELT has come.

At first, we can see only a skeletal steel dome, which over the course of the year has been gradually coated in a shiny new layer of protective — and thermally insulating — cladding. Panel by panel, the enormous 80 m high, 93 m wide structure is being wrapped in a warm blanket of aluminium and other thermal regulators. This will help to keep the air inside the telescope at the expected temperature of the next night, and defend it from the sand and dust of the ELT’s harsh desert environment. 

But that's not all, as this timelapse also shows how much progress has been made building the ELT’s main structure. Growing like a great white crystal at the dome's core, this lightweight and durable behemoth will one day house the ELT’s mirrors. At the base of this is the enormous 39 m wide cell structure, built to hold all 798 segments of the primary mirror, M1. The M1 is a feat of astronomical engineering, designed to gather tens of millions of times as much light as the human eye and focus it along a path through the ELT’s four other mirrors. Three of them will be housed in a sturdy central tower that was recently installed.

There was also plenty to celebrate in 2024 which hasn’t been captured in this timelapse. For example, in January the first segments of the M1 arrived in Chile, which were then coated with reflective silver later in March. A few months later, the (unpolished) blank of the fifth mirror, M5, was completed, and the cell that will hold it (while adjusting the position of the mirror up to 10 times a second) finished construction in September. In the same month, the last of 6 ELT laser sources was built — part of the telescope's adaptive-optics system, which will correct for atmospheric disturbances. Meanwhile, the development of the ELT’s scientific instruments has been barrelling forward, with METIS and MICADO passing their final design reviews, and the construction agreement for ANDES being signed. With all of these fantastic achievements in just twelve months, we’re left to wonder: what great things might be in store for 2025?