20 Tons of Glass, Fresh from the Oven
Giant Magellan Telescope’s Third Mirror Unveiled at the UA Steward Observatory Mirror Lab.

By Daniel Stolte, University Communications
Dec. 6, 2013

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UA President Ann Weaver Hart and guests join in unveiling GMT mirror number 3.
UA President Ann Weaver Hart and guests join in unveiling GMT mirror number 3. (Photo: Carina Johnson/UANews)

The Giant Magellan Telescope’s third primary mirror was unveiled at the University of Arizona’s Steward Observatory Mirror Lab on Friday, with UA President Ann Weaver Hart cutting the ribbon separating a 25-foot glass dish from an applauding crowd of invited guests and journalists. 
The third mirror – dubbed GMT3 – was cast in August at the mirror lab, the only facility in the world capable of creating mirrors of this size. Only a few days ago, technicians at the lab lifted the lid off the rotating furnace, removing a mold in which 20 tons of molten borosilicate glass slowly cooled into the desired parabolic shape, under the close watch of mirror lab staff to make sure the nascent mirror took shape free from any flaws such as gas bubbles, impurities or even cracks. 
Hart emphasized the lab's central role in bringing together people across disciplines and forging multiple partnerships to work on cutting-edge science and out-of-the-box thinking. 
"This lab represents the center of the science for the Giant Magellan Telescope project," Hart said. "Our students are deeply engaged in building this telescope, and patents and new businesses are spinning out of this endeavor."
Primary mirrors are the heart of the modern day reflecting telescope. They capture and focus photons coming from space to help construct images of the universe and collect complex spectra. Generally, the larger the surface area of the primary mirrors, the more photons they can collect, leading to better images and improved data collection. Once completed, the telescope will boast 10 times the resolution of the Hubble Space Telescope. 
Each of the Giant Magellan Telescope’s mirrors is the product of cutting-edge technology and processing. Cast in a custom-built rotating furnace that reaches approximately 2,100˚ Fahrenheit, they weigh about 20 tons, yet their internal architecture features an intricate honeycomb pattern that allows them to regulate temperature quickly while remaining extremely rigid. 
"The successful casting of GMT3 is a milestone for the UA because it puts us halfway through the production of the largest telescope in the world," said Joaquin Ruiz, dean of the College of Science. "It continues to put the UA at the forefront of the science and the technology that we need to create the instruments that allow us to test many of the hypotheses and observations astronomers have made so far."
The next step in the process is to hoist GMT3 out of the furnace, turn it upright and blast out the honeycomb molding scaffold by power washing. The mirror then will spend until 2018 slowly rotating on a carousel while computer-controlled polishing heads smooth its surface to the extent where if the mirror was the size of the continental U.S., the tallest hill would amount to an inch. 
The combined surface area of the three mirrors created to date already surpasses that of any existing telescope and will enable astronomers to peer more deeply into space than ever before. Among the first of a new generation of “extremely large telescopes” or ELTs, the Giant Magellan Telescope will have a mirror array consisting of seven mirror segments that are 25 feet in diameter, or 8.4 meters. The telescope is anticipated to begin operation in 2020 with four mirror segments completed, making it the largest telescope in the world. 
The Giant Magellan Telescope will be constructed at the Las Campanas Observatory in the Atacama Desert in northern Chile, where it will operate synergistically with other astronomical instruments and surveys. The instrument is designed to observe for more than 50 years and will help answer some of humanity’s most fundamental questions, including whether life exists on other planets and how the universe began. Astronomers also will use it to better understand how planets and galaxies form and to help find answers to the mysteries of dark matter and dark energy.  
"This is modern cathedral-building," said Buell Jannuzi, director of the UA's Steward Observatory. "Many of those involved in this project now may not get to use it during their lifetimes. We're building this telescope for future generations of researchers." 

Extra info

Details of the mirror making process can be seen in this video.


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