Long-Term Commitment

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Long-Term Commitment

Making a mirror for a giant telescope requires a long-term commitment. Back in March, for example, GMT — the Giant Magellan Telescope — began work on the sixth of its mirrors. It’ll take about three years to finish the job.

GMT will use a total of seven mirrors. They’ll work together to act as a single mirror about 80 feet in diameter — far larger than any current telescope. That will allow GMT to see stars and galaxies that are much fainter and farther, greatly expanding our view of the universe.

Each mirror is cast in a circular furnace at the University of Arizona. About 20 tons of a special glass is heated to more than 2100 degrees. The furnace rotates, sculpting the molten glass to the proper shape.

It takes about three months for the mirror to cool. Technicians then spend more than two years grinding and polishing it. The surface has to be smooth to within a millionth of an inch. Buddy Martin, who leads the process, described that level of accuracy during a March press conference.

MARTIN: If the mirror were expanded to the size of North America, 3500 miles in diameter, then the average hill would be two-thirds of an inch tall and the average valley two-thirds of an inch deep. That’s how smooth this mirror has to be for it to make the sharpest images that nature will allow.

All the mirrors are scheduled to be sent to GMT’s mountaintop site, in Chile, late in the decade.

Script by Damond Benningfield

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