A mirror so precise it could spot a coin from a kilometre away

Japanese scientists have built X-ray mirrors sharp enough to pick out a 3.5-millimetre detail from a full kilometre off — technology that lets a sounding rocket called FOXSI see the Sun's hottest, most violent moments in crisp detail. Published in the Publications of the Astronomical Society of the Pacific, the work could sharpen everything from solar-storm forecasting to deep-space X-ray astronomy.