Free Astronomy Magazine September-October 2019

23 SEPTEMBER-OCTOBER 2019 SPACE CHRONICLES T his is the first segment blank for mirror 1 (M1) of the ELT. Manu- factured by SCHOTT, it was com- pleted at the end of August 2018. M1 is the primary mirror of the ELT and, when completed, will be 39 metres in diameter and consist of 798 segments. The ELT is a revolu- tionary project that will allow as- tronomers to obtain images of larger planets and characterise their atmospheres, possibly enabling de- tection of biomarkers that could in- dicate life on other planets. [ESO] of the low-expansion glass-ceramic Zerodur © and are circular, measuring 1.5 metres across and about 5 cen- timetres thick. The back of each blank is flat and the front surface is concave. The blanks come in three types with slightly differently shaped front surfaces, depending on the planned location of the segment in the primary mirror. The first primary mirror segments were cast by SCHOTT in 2018. SCHOTT manufac- tures the blanks to approximate shape so that Safran Reosc does not need to remove too much material during the polishing process. Safran Reosc will polish the blanks before they are cut into hexagons and re- ceive a final precise polishing using Ion Beam Figuring . When it is com- pleted, the primary mirror will com- prise 798 hexagonal segments and will have a total light-collecting area of 978 m 2 . In total, more than 900 segments will need to be cast and polished (including a spare set of 133 segments). Once built the ELT will be the largest ground-based tele- scope in operation. The telescope is being built at Cerro Armazones in the Atacama Desert of northern Chile. With a primary mirror almost 40 metres in diameter, the ELT will gather almost 100 million times more light than the human eye, which will allow scientists to tackle some of the biggest challenges in current astrophysics, such as the for- mation of the first stars, the assem- bly of the first galaxies, the char- acterisation of the atmospheres of Earth-like exoplanets, or the nature of dark matter and dark energy, among many other questions. shock sensors travel with the blanks to measure any sudden acceleration or shock that could affect the blanks. The shipping container with the first 18 blanks was sent from SCHOTT in Mainz, Germany, on 23 July and ar- rived at Safran Reosc the following day. The ELT mirror blanks are made !