The framework for greatness

Bathed in the sunset light of Chile’s Atacama Desert, this Picture of the Week shows steady progress in the construction of ESO’s Extremely Large Telescope (ELT).

From up here, the ELT’s white tube-like altitude structure is clearly the eyecatcher. The close-knitted truss structure at the bottom is the support cell of the ELT’s 39-m primary mirror, the largest telescope mirror ever made. The light it collects from the cosmos will bounce off to the secondary mirror, which will be held in the central ring seen at the very top of the picture. Light will then travel down again through the ELT’s central tower and its three additional mirrors, before it reaches the scientific instruments that will be located at the side of the telescope.

At first glance, with no humans or bananas for scale, the steel structure might look modest in size. But the altitude structure alone is already more than 50 metres high, and the roof opening is 41 metres wide. If you want to take the stairs and walkways from the entrance of the ELT’s dome all the way up to the top, you need about 30 minutes. Now that’s what we call a workout!