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Mirror Lab workers load 51,900 pounds of glass into mirror mold.

The University of Arizona's Steward Observatory Mirror Laboratory is about to cast a new kind of giant optic for a unique wide-field survey telescope, the Large Synoptic Survey Telescope. The telescope will be the widest, fastest, deepest eye of the new digital age.

 Mirror Lab workers will begin loading 51,900 pounds of glass into the mirror mold early today.

The Mirror Lab will cast two mirrors as a single piece of glass for the telescope, known as the LSST, this month. The lab will cast an outer 27-foot-diameter (8.4 meter) primary mirror and an inner 16.5-foot-diameter (5 meter) third mirror in one mold. It is the first time a combined primary and tertiary mirror will be produced on such a large scale.

The LSST will be the world's largest, most powerful wide-angle survey telescope. It will provide time-lapse digital imaging across the entire available night sky every three days, enabling astronomers anywhere simultaneous access to study supernovae, planet-approaching asteroids or comets and other dynamic celestial chance events, and explore the nature of dark matter and dark energy.

Normally, big telescopes see a patch of sky the size of a tiny piece of Earth's moon. The LSST will see a section of sky roughly 40 times the size of the full moon. Each image will be recorded at high resolution by a 3.2 billion-pixel camera arrayed in a 2-foot (64 centimeter) detector, the world's largest.

The LSST will be built on Cerro Pachón, an 8,800-foot, or nearly 2,700-meter, mountain peak in northern Chile. Private and public partners, collaborating as the LSST Corp., plan to begin the survey in 2014 or 2015.

The LSST will use three mirrors. The outer region of the 27-foot primary mirror will collect celestial light and reflect it up to the separate 11-foot (3.4 meter) secondary mirror. The secondary mirror bounces light back down to the telescope's 16-foot tertiary mirror, which then sends it up again into a camera at the center of the secondary mirror. This complex down-up, down-up optical light path is needed to acquire the wide field-of-view.

The conservative approach would have been to cast the first and third LSST mirrors separately, Mirror Lab Director and Regents' Professor of Astronomy Roger Angel said. Ten years ago, he proposed the telescope design that has evolved into the LSST.

"But it costs almost as much to cast a 5-meter third mirror as it does to cast an 8-meter primary," Angel said. "If we put these in the same piece of glass, that saves how much glass you have to use all together, as well as the time it takes to cast two mirrors."

Another, possibly greater, advantage is that by making the two mirrors in one, the two mirrors can be precisely aligned once and for all in the laboratory, Angel said. "So we'll save money both in the manufacture of the mirrors and also over the lifetime of the telescope because of the simplicity of permanently holding the mirrors in proper alignment."

Financial support for LSST comes from the National Science Foundation (NSF) through Cooperative Agreement No. 1258333, the Department of Energy (DOE) Office of Science under Contract No. DE-AC02-76SF00515, and private funding raised by the LSST Corporation. The NSF-funded LSST Project Office for construction was established as an operating center under management of the Association of Universities for Research in Astronomy (AURA).  The DOE-funded effort to build the LSST camera is managed by the SLAC National Accelerator Laboratory (SLAC).
The National Science Foundation (NSF) is an independent federal agency created by Congress in 1950 to promote the progress of science. NSF supports basic research and people to create knowledge that transforms the future.


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