Solar eruptions trigger aurorae on Earth, filling the night sky at high latitudes with dancing lights.

BBC: Sun, Trace

They make aurorae visible at far lower latitudes than usual.

ECONOMIST: Hot stuff

The so-called Carrington Event of 1-2 September 1859 shorted telegraph wires, starting fires in North America and Europe, and caused bright aurorae (northern and southern lights) to be seen in Cuba and Hawaii.

BBC: Four colossal Sun flares in 48 hours