Meet the World’s Biggest Telescope


The view from the remote, barren Andes Mountains in northern Chile stretches for miles, over waves of bare, dun-colored peaks rolling to each horizon. More importantly, Las Campanas Observatory, at an elevation of almost 8,000 feet beneath famously dark and clear skies of the Atacama Desert, enjoys unparalleled views of the night sky. That led astronomers to select this site for the observatory and, more recently, the Giant Magellan Telescope.

First in a new class of extremely large telescopes, construction on the GMT broke ground last month. The telescope will combine seven giant mirrors and use adaptive optics, a system that makes minute changes in the shape of the secondary mirror thousands of times per second to remove blurring caused by Earth’s atmosphere. The result: resolution 10 times greater than the Hubble Space Telescope.|

That power will allow astronomers to see and study light from shortly after the Big Bang, some 14 million years ago. Scientists will be able to make observations with this telescope that are impossible to do with any other facility, says Taft Armandroff, director of UT’s McDonald Observatory and chair of the board of directors for the Giant Magellan Telescope Organization. That organization includes institutions from Australia, Brazil, and Korea, plus the Carnegie Institution for Science, Harvard University, Smithsonian Institution, Texas A&M University, the University of Arizona, and the University of Chicago, in addition to UT.

“The GMT will revolutionize two fundamental areas that drive a lot of research at UT and worldwide in astronomy—the study of exoplanets and investigation of how long it took stars and galaxies to form after the Big Bang,” Armandroff says.

Only 20 years have passed since the discovery of the first exoplanet—a planet revolving around a star other than our own—and the GMT greatly advances the technology for detecting and studying these bodies. The telescope can concentrate light from an exoplanet to a tiny point and take a precise spectrograph, or map of different wavelengths of that light. These spectrographs can indicate whether a planet has an atmosphere and if so, what it contains.

“The holy grail is a spectrum of an Earth-like planet, with oxygen and water,” Armandroff says. “This will help us understand basic questions about how often planets about the size of Earth form and whether they are conducive to life. There has been a scientific revolution in the study of exoplanets, and GMT takes it to the next stage.”

“This will help us understand basic questions about how often planets about the size of Earth form and whether they are conducive to life.”

The telescope’s 82-foot diameter primary mirror will include seven separate, 27-foot diameter segments, each weighing about 17 tons. The Richard F. Caris Mirror Lab at the University of Arizona is producing the mirrors, each of which takes a year to cast and cool and more than three years of surfacing and meticulous polishing. The third mirror is currently being polished and the fourth is now undergoing casting. The finished mirrors likely will travel by road to Los Angeles and from there via ship to Chile and again by road to Las Campanas.

Work now underway on the mountaintop includes providing utilities and constructing a residence facility. Excavation of foundations for the GMT will start next October, which is summer in Chile, followed by the pouring of concrete foundations to support the massive telescope dome. “First light,” or the first image from the GMT and launch of its scientific operations, is expected in 2021, with completion by 2024.

UT astronomers will employ the GMT one of three ways: by remote operations from a control center in Austin, by placing their observing needs into a queue to be executed by on-site professional astronomers, and by traveling to the site in person.

“Only 11 institutions will have access to this unique data, so it’s an added benefit for recruiting faculty and graduate students to UT,” Armandroff says. U.S. News & World Report recently ranked the university in the top 10 Best Global Universities for Space Science, he adds, and the GMT should move the university up in such rankings. “And, of course, answer some big questions. That’s what it’s really all about.”

Illustration: An artist’s concept of the completed Giant Magellan Telescope, which will be situated in the Atacama Desert some 115 km (71 mi) north-northeast of La Serena, Chile.

Image via Wikimedia Commons.


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