Observers gather around to look at the third mirror for the Giant Magellan Telescope at the University of Arizona’s Steward Observatory Mirror Lab before a ceremonial unveiling celebrating the latest stage in the 27-foot mirror’s formation. 

Kelly Presnell / Arizona Daily Sta

Officials from the University of Arizona and the Giant Magellan Telescope Organization gathered Friday to lift the lid on the third of seven giant pieces of glass that will ultimately form the world’s largest telescope.

The telescope, to be installed on a mountaintop in Chile, will combine the light-gathering power of seven 8.4-meter (27 feet) mirrors.

Cast in the Steward Observatory Mirror Lab beneath the east bleachers of Arizona Stadium, each mirror is formed from 20 tons of heated glass that flows into a honeycomb structure in a rotating furnace. The pieces then cool for about six months.

The polishing of the GMT’s asymmetrical sections is a technological task that takes five to six years to complete.

The mirror unveiled Friday is expected to be ready for shipment in 2018.

The mirrors are ultimately bound for a peak in northern Chile’s Atacama Desert at Carnegie’s Las Campanas Observatory.

The total cost of the eight mirrors, including a spare, will be $150 million to $170 million.

The UA is a partner in the Giant Magellan Telescope Organization.

Other partners include Astronomy Australia, Australian National University, Carnegie Institution for Science, Harvard University/Smithsonian Institution, Korea Astronomy and Space Science Institute, the University of Texas, Texas A&M University and the University of Chicago.

Contact reporter Tom Beal at or 573-4158.