Hot Stuff! Huge Secondary Mirror Cast for Extremely Large Telescope
By Sarah Lewin, Staff Writer | May 24, 2017 07:00am ET
An enormous piece of glass-ceramic has been cast for the secondary mirror of the European Southern Observatory's (ESO) Extremely Large Telescope, entering a year-long cooldown and heat-treatment period until it's ready to be ground and polished for use with the megatelescope.
The completed mirror will measure nearly 14 feet across (4.2 meters) and weigh 3.9 tons (3.5 metric tons) — larger than the primary mirror for many current research telescopes, ESO officials noted in a statement. For the Extremely Large Telescope, though, the mirror will be suspended upside down over the 128-foot (39 meter) primary mirror, which is made of 798 hexagonal mirror segments. The telescope is scheduled to reach first light in 2024 on a mountain in Chile's Atacama Desert. ESO documents the casting process in a new video.
- click for photo -
https://img.purch.com/h/1400/aHR0cDovL3d3dy5zcGFjZS5jb20vaW1hZ2VzL2kvMDAwLzA2Ni8xNTAvb3JpZ2luYWwvZWx0LW1pcnJvci1tb2xkLmpwZz8xNDk1NDg3NTIz
After the year of cooling, the mirror base will be transported from Germany to France, where it will be ground into a precise convex shape and then polished precisely to within 15 nanometers to meet the giant telescope's needs. According to the ESO, the piece will be the largest convex mirror ever produced and the largest secondary mirror to be used in a telescope.
More:
http://www.space.com/36952-extremely-large-telescope-secondary-mirror-cast.html
Science:
https://www.democraticunderground.com/122852164
