For space-weather scientists, the auroras, created by a raging solar storm, were long-expected but dramatic evidence that the Sun is nearing the peak of its 11-year cycle of activity.

Satellite operators, electrical-grid managers and others who maintain crucial technological infrastructure are still assessing the impacts of this historic event — the severest geomagnetic storm since 2003. But most major systems seem to have weathered the blast.

That’s encouraging, because more storms are likely: the most powerful geomagnetic storms of a solar cycle can occur after the ‘solar maximum’, which is expected later this year. Nature explains what happened over the past few days and what solar physicists are anticipating next.

Starting around 8 May, active region 3664 sent at least seven blasts of magnetized plasma, or coronal mass ejections, racing in Earth’s direction at speeds of up to 1,800 kilometres per second. Along with other waves of charged plasma and solar debris, the coronal mass ejections swamped space-weather detectors. The experience was “hypnotic”, says solar physicist Ryan French at the National Solar Observatory in Boulder — first watching the data flood in, and then later because of the “raw awe” of witnessing the aurora.

When could the next big storm affect Earth?
At any time. Scientists expect the current solar cycle to peak some time this year, owing to the number of sunspots they are observing. The biggest storms typically happen months to years after this official peak. Furthermore, as the solar cycle progresses, sunspots tend to appear closer to the Sun’s equator, increasing the chances of coronal mass ejections that will head directly for Earth rather than out into space, Dahl says.