Insights: Breaking the Mold; December 2005; Scientific American Magazine; by W. Wayt Gibbs; 2 Page(s)
Not long after he founded the Mirror Laboratory at the University of Arizona's Steward Observatory in 1984, astronomer Roger Angel threw some Pyrex custard cups into a backyard kiln to get a feel for how borosilicate glass melts. He has been playing with fire ever since. On a sweltering July day in Tucson, his seventh giant mirror takes shape in a 200-ton rotating oven underneath the campus football stadium. After a week of heating, the borosilicate blocks in the oven have reached 1,170 degrees Celsius and begun to liquefy, sending molten glass seeping over hexagonal pillars to form a 21-ton honeycomb that is 8.4 meters (28 feet) in diameter, roughly a meter high, but nowhere thicker than three centimeters.
Usually Angel would be in the control room, nervously watching the hot, red carousel spin five times a minute, just fast enough to pull the solid top of the glass honeycomb into the desired gentle curve. To Angel, after all, this process represents the birth both of a new era of astronomy and of the Giant Magellan Telescope (GMT), which, by banding together seven huge mirrors with sophisticated control mechanisms, would outdo the Hubble Space Telescope. And the first time his team made a mirror of this size, the mold leaked two tons of glass, causing months of delay. This first GMT mirror is trickier still, Angel explains, because "it is wickedly curved into an extreme shape that no one has ever made before at this scale."