Making the Giant Magellan Telescope's Massive Incredibly Precise Mirrors

By Sarah Lewin, Space.com | January 18, 2017 
The largest single-piece astronomical mirrors ever made are slowly coming together for an eagle-eyed ground-based telescope.
To focus images for the Giant Magellan Telescope (GMT), which is under construction in Chile, the 27.6-foot-wide (8.4 meters) concave mirrors must be curved precisely, to within 20 nanometers — the width of a single glass molecule. When completed, the telescope will return images 10 times sharper than those of the Hubble Space Telescope.
At the American Astronomical Society's winter meeting in early January, Space.com caught up with the GMT's director, Pat McCarthy, as well as Buell Jannuzi, head of astronomy at the University of Arizona and director of its Steward Observatory, whose mirror lab is turning out the 20-ton (18 metric tons) glass mirrors. The duo discussed the progress of construction on the immense optical telescope and the demanding mirror-crafting process, plus the science they're most looking forward to from the telescope's start of operation, which could happen as early as 2023.
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