2024-07-17 06:00:11
The European Southern Observatory’s Extremely Large Telescope (ELT), under construction in the Chilean Atacama Desert, is nearing completion. The German company SCHOTT has successfully cast the last of the 949 segments ordered for the primary mirror of the telescope. telescope (M1). With a diameter At over 39 meters, M1 will be by far the largest mirror ever made for a telescope.
Image ESO
Too large to be made from a single piece of glass, M1 will consist of 798 hexagonal segments, each about five centimeters thick and 1.5 meters in diameter, that will work together to collect tens of millions of times more light than the human eye.
An additional 133 segments were produced to facilitate maintenance and segment coating once the telescope is operational. ESO also purchased 18 spare segments, bringing the total number to 949.
The M1 blanks, shaped parts that are then polished to become the mirror segments, are made of ZERODUR©, a low-expansion glass-ceramic material developed by SCHOTT and optimized for the extreme temperature ranges at the ELT site in the desert Atacama. This company also manufactured the blanks for three other ELT mirrors – M2, M3 and M4 – at its facilities in Mainz, Germany.
The 949th ELT mirror segment is cast and ready to take shape
Once cast, all segments follow a multi-stage international route. After a slow cooling and heat treatment sequence, the surface of each blank is shaped by ultra-precise grinding at SCHOTT. The blanks are then transported to the French company Safran Reosc, where each one is cut into the shape of ahexagon and polished with a precision of 10 nanometers over the entire surface optical – which means that the irregularities of the mirror surface will be less than one thousandth of the width of a human hair.
Once polished and assembled, each M1 segment is shipped across the ocean to the ELT’s technical facility at ESO’s Paranal Observatory in the Atacama Desert – a 10,000-kilometre journey that more than 70 M1 segments have already completed. At Paranal, just a few kilometres from the ELT’s construction site, each segment is coated with a layer of silver to make it reflective, after which it will be carefully stored until the telescope’s main structure is ready to receive it.
When it begins operation later this decade, ESO’s ELT will be the world’s largest eye on the sky, tackling the greatest astronomical challenges of our time and making previously unimaginable discoveries.
The Arc de Triomphe in Paris enters under the ELT’s crown. In the center, the current Very Large Telescope (VLT).
Image Wikimedia
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