On the night of Saturday 17 May, skywatchers across the US as far south as New Mexico were treated to a peculiar sight: a brilliant stream of whitish light, stretching across the sky.

That was a night for auroral activity, as Earth’s magnetic field was buffeted by an influx of particles ejected from the Sun several days earlier. Initially, explanations favored STEVE, the name given to the white-mauve streaks of light emitted by rivers of charged particles flowing through Earth’s ionosphere.

STEVE is not an aurora, but, like the auroral displays it often appears alongside, is also a product of space weather.