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Steward Observatory casts second mirror for Giant Magellan Telescope

Lydia Stern, Heather DiPietro | Arizona Daily Wildcat

The second mirror for the Giant Magellan Telescope was cast in the Steward Observatory Mirror Laboratory on Saturday, January 14th.

The second mirror for the Giant Magellan Telescope was cast in the Steward Observatory Mirror Laboratory on Saturday.

The Giant Magellan Telescope, which began its design phase for the mirrors in 2005, will have 10 times the resolving power of the Hubble Space Telescope, and, once operational, will equate to 100 billion people looking at the sky at one time. Once components of the telescope are constructed, they will be transported to Chile, and the entire unit will be assembled and situated atop Las Campanas peak in the Andes Mountains as part of the Las Campanas Observatory. From here, astronomers will be able to view the southern hemisphere free from light pollution and other disturbances.

Photo: Robert Alcaraz

Robert Alcaraz/ Daily Wildcat

A conference held for the promotion of a Mirror Casting Event for the Giant Magellan Telescope in the UA Steward Observatory on Saturday, Jan. 14, 2011. The mirror is to be the second mirror cast for the telescope.

The 27-foot mirror was the second of seven primary mirrors to be cast since the project’s inception in 2005. The remaining primary mirrors will also be cast at the mirror lab, which, according to Pat McCarthy, the project’s director, is the only place this project can be done.

“The UA has just a fantastic astronomy department that has such a long history both in building telescopes and using them to do great science that they’re a natural partner,” McCarthy said. “Under Professor (Roger) Angel, they’ve really developed this unique, one-of-a-kind capability to make large, astronomical optics that have just superb performance. We wanted to build a really big telescope like this and do it in a university environment; the U of A is the only place to do it.”

The casting process for one mirror takes 12 to 13 weeks. While about 20 tons of glass are used to produce each mirror, the final product is much lighter, as it is molded using a honeycomb pattern which provides a stable, yet lightweight structure. The glass is then heated to about 2,156 degrees and spun in a rotating oven where it flows as a liquid into the mold. While spinning, the mirror takes the desired concave shape, then finally becomes rigid during the 11 to 12-week cooling process. After being ground and polished, it is transported to the site by truck where it is mounted and tested.

According to Peter Strittmatter, the Steward Observatory director and member of the Giant Magellan Telescope Organization board of directors, it is theoretically possible to make the mirrors larger, but mirrors with a larger diameter wouldn’t fit through the mirror lab’s bay door, and would be nearly impossible to transport.

Funding for the $700 million project is split between partners, who usually pay 10 percent of the construction and operation costs and receive a 10 percent share for usage of the telescope, according to McCarthy. Different partners get their funding from various sources, McCarthy said. The U.S. receives its funding from gifts or financial resources within universities. Recently, a contribution of $25 million was made by George P. Mitchell, founder of the Mitchell Energy and Development Corporation. Mitchell’s contribution paid for the majority of the first mirror, which has been named after him.

According to scientists working in the mirror lab, constructing the mirrors at the UA adds to the university’s reputation and prestige as an institution known for making groundbreaking advancements and discoveries.

“We are making one of the single-most challenging and expensive parts of the telescope,” Strittmatter said. “It clearly continues to send a loud message to the world as to what a great place the University of Arizona is … Like any other research field, you always have to be moving forward with more powerful instrumentation; otherwise, you get left behind with the others. For us, this represents a key step forward to ensure that we remain at the cutting edge.”


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