The Mirror Lab: Casting the Eyes of the World's Largest Telescopes

Beneath the east stands of Arizona Stadium, the University of Arizona football venue that holds more than fifty thousand people, is one of the most specialized manufacturing facilities on earth. It is called the Richard F. Caris Mirror Lab, and it makes primary mirrors for the world's largest telescopes.

Roger Angel, a University of Arizona astronomer, developed the spin-casting technique in the nineteen eighties. The process begins with chunks of borosilicate glass loaded into a ceramic honeycomb mold inside a rotating furnace. The furnace heats to about eleven hundred and sixty-five degrees Celsius, melting the glass, and spins at a rate precisely calibrated to the curvature the final mirror requires. The centrifugal force shapes the molten glass into a parabolic surface. When the furnace cools over several months, the result is a single-piece honeycomb mirror, lightweight relative to its size, with a precisely curved face ready for optical grinding.

The Mirror Lab produces mirrors up to eight point four meters in diameter, about twenty-seven feet across. There is no other facility in the world producing primary mirrors at this scale. Mirrors from this lab sit at the heart of the Large Binocular Telescope on Mount Graham in southeastern Arizona, the Magellan Telescopes in Chile, and are being fabricated for the Giant Magellan Telescope, which when complete will be among the largest optical telescopes on earth.

All of this happens under the seats where tens of thousands of people watch football on autumn Saturdays, with no particular awareness of what is spinning below them.