The Sun has regions that resemble an overheated boiler: magnetic fields there twist into tight ropes and store energy. Every so often, a rope snaps, and a flare erupts, a powerful explosion that hurls streams of charged particles into space. Such blasts can knock out satellites and disrupt communications on Earth.

Scientists have devised a way to anticipate where a rope is about to break. They monitor small, bright ultraviolet flashes — visible only to specialized telescopes and lasting from a minute to an hour. It turns out that in regions where a major eruption will occur within hours, these flashes are five times more frequent than in quiet areas. It's as if light bulbs started flickering frequently in one neighborhood before an earthquake.

So far, the method has been tested on two regions of the Sun: one produced a powerful flare, the other remained quiet. The result is encouraging: in the hours before the eruption, the number of small flares rises sharply. If confirmed with more observations, space weather forecasts could become more accurate, and satellites and power grids on Earth would be safer.