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First six segments of Extremely Large Telescope cast

The first six mirror segments of the European Southern Observatory’s Extremely Large Telescope have been successfully cast.

These segments will form parts of the ELT’s 39-metre main mirror, which will have 798 segments in total when completed. The ELT will be the largest optical telescope in the world when it sees first light in 2024.

The 39-metre-diameter primary mirror of ESO’s Extremely Large Telescope will be by far the largest ever made for an optical-infrared telescope. Such a giant is much too large to be made from a single piece of glass, so it will consist of 798 individual hexagonal segments, each measuring 1.4 metres across and about 5 centimetres thick. The segments will work together as a single huge mirror to collect tens of millions of times as much light as the human eye.

The segments must now be cooled, then their surfaces ground and polished to the right shape. If all goes right, they will make more than 900 segments (with about a 130 as spares), manufactured to have the telescope operational by 2024.

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