Richard F. Caris Mirror Lab

Beneath the east stands of Arizona Stadium, where you'd least expect to find precision optics, scientists spin-cast the world's largest telescope mirrors in a rotating furnace hot enough to melt borosilicate glass. The work began around 1980 with Dr. Roger Angel's backyard experiment — fusing two custard cups in a kiln to test honeycomb casting — and moved under the stadium by 1985 on USAF, NSF, and University of Arizona funding. What started as a kiln experiment is now the Richard F. Caris Mirror Lab, the only facility on earth producing mirrors this size for the telescopes that will peer deepest into the universe.

The mirrors have a honeycomb structure inside — made from Ohara E-6 low-expansion glass melted into honeycomb form while the furnace spins. Honeycomb construction gives these mirrors the rigidity and stability of solid glass but allows them to be dramatically larger and lighter. The lab pioneered rotating-furnace spin casting, a technique that shapes the mirror's curve as the molten glass cools. Mirrors cast here have gone into the Magellan telescopes, the Large Binocular Telescope, and seven primary mirrors are under construction for the Giant Magellan Telescope — instruments that will explore the cosmos in optical and infrared light with unprecedented surface accuracy.

Tours run regularly; you enter through Gate 4 on the stadium's east side. The lab website posts the schedule. What you see is the working floor — not a museum exhibit but the actual casting bays, polishing stations, and the furnace that produces mirrors up to 8.4 meters across. The mirrors being finished today will still be gathering starlight a generation from now, long after the team that cast them has retired. If you want to see where Tucson's engineering tradition meets the edge of what's technically possible, this is the room.