Hot and dry air, perfused with a scent reminiscent of a warmed hair straightener, stuffed a hangar-sized room beneath the football stadium at the University of Arizona. The space, part of the Richard F. Caris Mirror Lab, was dominated by a gyrating, carousel-sized furnace, fire truck red and shaped like a flying saucer. The swirling cocoon of a colossal light collector.

“It’s making 4.9 revolutions per minute,” says astronomer Buell Januzzi of the University of Arizona, raising his voice over the lab’s droning ventilation system. About half past noon on October 7, after about a week of gradual warming, the temperature inside the rotating machine had finally peaked at 1165° Celsius.

In the heart of that inferno, nearly 17,500 kilograms of borosilicate glass — roughly four semitruck loads — had melted into a crystal clear fluid. If all goes to plan, the molten material will anneal to form the body of an enormous mirror — one as tall as a two-story house, if stood on edge. The mirror is the last of seven needed to capture light for what will be the world’s most powerful optical instrument, the Giant Magellan Telescope.

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