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A mirror with a view

Mount graham’s telescope is the first of a new generation.

TUSCON, Ariz. – Rarely do the subjects of French cuisine and astrophysical optics overlap. But for Peter Wehinger, telescope mirrors and egg dishes are not mutually exclusive.

“Constructing a mirror is like making a largely elaborate and elegant souffle,” said Wehinger, a University of Arizona astronomer and staff development officer. “It’s all in the details.”

Astronomers in the Mount Graham International Observatory project, in which the University participates, said the completed telescope will represent the latest and grandest innovations in large telescopes.

Peter Strittmatter, the University of Arizona’s Steward Observatory director, said the telescope will be the first of a new generation of telescopes.

The telescope will allow researchers to view faint objects in space, as well as ones farther away.

“Astronomy has been moving steadily outwards in what it can observe,” Strittmatter said. “We will be seeing back 90 percent, to when the universe was only about 10 percent of its current age.”

Astronomy professor Charles Woodward said he came to the University of Minnesota almost five years ago to access the telescope through its Mount Graham partnership.

Besides peering back in time, Woodward said the large telescope can dim down stars’ light to provide a better view of a star’s orbiting planets. It could one day find planets with light signatures similar to the Earth’s.

“Over the course of a few years, that likelihood is pretty reasonable,” Woodward said.

At the heart of the telescope innovation are dual 28-foot mirrors that will produce the farthest-reaching and clearest universe images to date.

It all started beneath the University of Arizona’s football stadium, where the mirror lab resides and scientific souffles are born.

The mirrors in the telescope represent a new breed of telescopic mirrors, said Richard Green of the Kitt Peak National Observatory, a collection of Arizona-based telescope facilities.

Green said the mirror lab created the spin-cast technique, which is slowly spreading to high-grade telescopes around the globe.

“They remain the only enterprise that produces giant mirrors with that pioneering technique,” Green said.

The process, Wehinger said, first involves melting down 20 tons of camera-lens quality glass blocks.

As the glass melts down over a few weeks in a large holding container, it is spun to fill a special mold.

After reaching a peak temperature of 2,000 degrees and cooling for three months, the mirror is carefully removed from the container, Wehinger said.

It takes many months to turn disparate softball-sized chunks of glass into these enormous, rigid, lightweight mirrors, he said.

The mirrors produced in the mirror lab have an edge over their predecessors, Wehinger said. An inch thick, they can stay rigid and strong. The thinness makes them more adaptive to weather changes.

The telescope’s mirrors will also use adaptive optics, which enables astronomers to clear out atmospheric air clutter that has hindered Earth-based telescopes from getting images comparable to ones in outer space, Wehinger said.

Achieving the impossible

The evolution of these giant mirrors began approximately 20 years ago when the University of Arizona’s Steward Observatory approached a glass company about manufacturing lightweight telescopic mirrors, Strittmatter said.

“People told us it was impossible,” he said. “We like achieving the impossible.”

A University of Arizona astronomer first made one in his backyard barbecue, Wehinger said. The mirrors have a honeycomb-like structure on one side instead of two smooth faces.

“The bees know how to do it right,” he said. “They make honeycomb structures because they are very stable.”

After the cooling, solidifying and polishing processes, a vacuum is placed over the mirror and a layer of vaporized aluminum approximately 10 to 20 atoms thick settles on it, said Len Kuhi, head of the University’s astronomy department.

The aluminum gives the mirror its reflective and light-gathering capabilities, he said.

The University of Arizona already owns or operates 15 Earth-based telescopes. They vary in imaging ability and function, Kuhi said.

Through the Mount Graham International Observatory project, the University has access to all of these.

They include the Magellan telescopes at Las Campanas Observatory in the Chilean Andes, with its two 19.5-foot wide mirrors that were spun cast at the mirror lab.

Although the mirror lab’s lightweight mirrors are now spreading to telescopes throughout the world, Green said older telescopes are not obsolete simply because of this new technology.

They are useful for other astronomical purposes and can be upgraded as needed. There is enough universe for all telescopes, he said.

“The universe is full of phenomena on all scales,” Green said. “I run a 30-year-old telescope, and it’s still one of the great instruments.”

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