In April, something went awry at the astronomical observatory atop Mount Graham, a 3,200-metre peak in Arizona. A valve got stuck open on a line that feeds coolant to a secondary mirror at the Large Binocular Telescope (LBT), a double-barrelled behemoth with two 8.4-metre-wide main mirrors. By the time anyone noticed, one of the telescopes smaller, secondary mirrors was coated in frost. When the ice melted, it ruined this thin mirror, which brings the LBT's double vision into exquisite focus.
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