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Public can scope out UA’s mirror lab

Citizen Staff Writer



Dan Pittenger long yearned to take a tour of the University of Arizona Steward Observatory Mirror Lab.

He finally got his chance Tuesday.

Pittenger was among a dozen people who paid $15 to learn what happens behind the scenes at the only lab in the world where large-format honeycombed glass telescope mirrors are spin-cast, polished and prepared to explore the extreme depths of the night sky.

“This is the first time we are making the mirror lab available to the public on a regular basis,” said Cathi Duncan, program coordinator at Steward Observatory, who organizes and schedules the tours.

Tour leader Vernon Dunlap explained how 21 tons of chunks of Japanese-made Ohara E6 borosilicate glass are placed in a mold in an oven, heated, spun and cast into precision optical devices in the lab, which is beneath the east side of Arizona Stadium.

The Steward lab is unique in manufacturing scope mirrors with a honeycomb structure that allows them to be one-fifth the weight of conventional solid glass mirrors, Dunlap said. The lab began operations in 1985 and expanded in 1990.

The mirror lab, which employs 45, offers UA a revenue stream, said Philip A. Pinto, UA professor of astronomy and member of the Large Synoptic Survey Telescope team.

UA is being paid $23 million to produce the 8.4-meter LSST mirror, Pinto said.

The lab also offers real-world experience for UA students studying optical science, engineering, astronomy and public health, Duncan said.

The lab is the only one in the world with a huge oven that spins the melted glass, which reaches the consistency of honey when heated to 2,129 degrees Fahrenheit, to form concave mirrors, he said.

Once the glass – which costs more than $18 per pound – is heated and spun at about seven revolutions per minute to fill the mirror form, it takes about 3.5 months of careful cooling before it can be removed for polishing.

Tour participants viewed work on two 8.4 meter mirrors, which are 26.7 feet in diameter.

One is destined for the Giant Magellan Telescope project in Chile that will use seven 8.4-meter mirrors gathering light to be sensitive enough to see a candle on the moon.

Another mirror under construction will be used in the LSST. The LSST scope, also to be located in Chile, will let astronomers image the entire available night sky every three days when it starts operating in 2015. Sky scan data collected will quickly be made available to the public so amateur, as well as professional, astronomers can participate in research.

“LSST could find 1,000 supernovas (bright stars that are blowing up) every night,” Dunlap said.

Mirror lab technicians use special polishing devices to produce mirrors so accurate they could be used to read a newspaper at a distance of five miles.

The 8.4-meter mirrors being produced at the lab have reached the maximum size limit based on transportability, he said.

While the lab has the capability to cast larger mirrors, they would be difficult to get out of the lab’s doors. And the mirrors are transported in a horizontal position by truck, taking up two freeway lanes, Dunlap said.

After the mirrors arrive at their observatory destination, the highly polished glass face is coated with a thin film of aluminum to reflect light, he said.

One beer can’s worth of aluminum is used to coat an 8.4-meter mirror 100 nanometers thick. A nanometer is one-billionth of a meter. The aluminum coating must be reapplied every two years, he said.

Tuesday’s tour visitors saw early preparations for the next mirror to be cast at the lab, a 6.5-meter mirror for Mexico’s National Astronomic Observatory at San Pedro Martir.

Steward Mirror Lab tour participants will be able to visit the lab during “high fire,” the casting phase when the glass chunks are heated enough to melt and flow into the mirror mold, Duncan said.

“This will be the first time the public has been able to experience this,” Duncan said.

The glass begins to flow at 1,290 degrees Fahrenheit, and the oven maxes out for about five hours at 2,129 degrees Fahrenheit before controlled cooling begins, said Karen Kenagy, program manager at the mirror lab.

The high fire phase is expected to occur in late 2009, Kenagy said.

People attending Tuesday’s tour said they enjoyed the experience.

Vanessa Thomas of Baltimore was visiting her sister Kristina Thomas, who lives in Phoenix, and the pair drove down to check out the mirror lab.

“I got to see where they are being made,” said Vanessa, who works in the astronomy industry.

Dan Pittenger, a retired electrical engineer from Richfield, Wis., seemed interested in each phase of mirror construction.

“I think the average person will get something out of it,” he said.

His wife, Judy Pittenger, was intrigued to learn how long it takes to produce large scope mirrors. An 8.4-meter mirror takes about four to five months to cast, which is followed by a lengthy grinding and polishing process.

“We hope to come back in October for the next casting,” she said.

Dan Pittenger was glad his dream of seeing the lab finally came true.

“I fought to get into here for five years,” Pittenger said.

He enjoyed the experience so much he wants to come back – again and again.

“If I move here, I might become a tour guide,” he said.

‘I fought to get into here for five years. . . . If I move here, I might become a tour guide.’


retired electrical engineer

Tours start at UA mirror lab

Lab mirror history

Casting Size

date meters (feet) Telescope/Observatory

1985 1.8 (5.9) Vatican Advanced Technology Telescope

1987 1.2 (3.9) Smithsonian Astrophysical Observatory

1988 3.5 (11.5) Astrophysical Research Consortium

1988 3.5 (11.5) Wisconsin-Indiana-Yale-NOAO

1989 3.5 (11.5) U.S. Air Force Starfire Optical Range

1992 6.5 (21.3) Multiple Mirror Telescope Conversion

1994 6.5 (21.3) Magellan I, Las Campanas Observatory

1997 8.4 (27.6) Large Binocular Telescope I

1998 6.5 (21.3) Magellan II, Las Campanas Observatory

2000 8.4 (27.6) Large Binocular Telescope II

2002 6.5 (21.3) Lockheed Martin Corp.

2005 8.4 (27.6) Giant Magellan Telescope I

2006 3.8 (12.5) Test Optic, Mirror Lab

2007 8.4 (27.6) Large Synoptic Survey Telescope


• What: Steward Observatory Mirror Lab tours.

• When: Tuesdays – Fridays, times vary

• Where: 527 National Champion Drive, under the east side of Arizona Stadium

• Cost: $15

• Reservations: Required, call 626-8792 or e-mail mirrorlab@as.arizona.edu

• Etc.: Participants must be at least 7 and must wear closed-toe shoes. Stairs are involved.

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