Aurora
Also called: northern lights, southern lights, aurora borealis.
Curtains of light in the sky near the poles, caused by solar particles hitting the upper atmosphere.
When gusts of charged particles from the Sun reach the Earth, its magnetic field funnels them towards the poles, where they make oxygen glow green and red and nitrogen pink and violet. Big geomagnetic storms push aurorae far from the poles — they have been seen from Greece and the Mediterranean in strong storms.
At the eyepiece
Cameras pick up aurorae better than the eye: a phone's night mode often shows colour that looks grey by eye.
In AstroPilot
Tonight shows the chance of an aurora for your latitude from NOAA's Kp forecast.