M1 segments begin their life at SCHOTT in Germany as blanks made of Zerodur ©, a glass-ceramic material that has very low thermal expansion. To achieve the required scientific performance, the mirror needs to be maintained in position and in shape to an accuracy of tens of nanometres - 10000 times thinner than a human hair - across its entire 39-metre diameter! This is extremely challenging, as the full structure will be moving constantly during an observation and will be affected by wind and thermal changes. Since the segments have to work together as a single mirror, they require specific infrastructure and control schemes. Too large to be made from a single piece of glass, the 39-metre-diameter mirror will consist of 798 segments, each about 5 centimetres thick, measuring close to 1.5 metres across and weighing 250 kg, including its support.
The M1 is, without a doubt, one of the most impressive and challenging aspects of the entire ELT project. It is the surface that will gather light from cosmic objects, opening up new discovery spaces - from exoplanets close to their stars, to black holes, to the building blocks of galaxies - both in the local Universe and billions of light years away.
M1, the ELT’s primary mirror, is the centrepiece of the revolutionary astronomy machine currently under construction in Chile's Atacama Desert.
