Why do the northern lights happen, and why were they seen so far south in 2024?

The northern and southern lights are caused by charged particles from the Sun hitting the atmosphere high above Earth. An aurora is a natural light display in Earth's upper atmosphere, made when those particles collide with atoms there. The collisions excite oxygen and nitrogen, which then give off light, mostly green, but also red and purple.

Most of the time the lights stay near the poles. Auroras are most common in a band about 6 degrees wide in latitude, centred on 67 degrees north and south. The southern lights, the aurora australis, look almost identical to the northern lights and change at the same time. What sets them off is a disturbance in Earth's magnetosphere from a faster solar wind or a coronal mass ejection.

When a big storm hits, the band swells and the lights spread much closer to the equator. In May 2024, the most powerful geomagnetic storm since March 1989, classed G5, produced aurorae at far lower latitudes than usual: in the United States as far south as the Florida Keys, and also in Mexico, the Bahamas, Jamaica and Puerto Rico. In October 2024 another storm, rated G4 by NOAA's Space Weather Prediction Center, brought a forecast of lights across the northern US and possibly as far south as Alabama.

The name comes from Aurora, the Roman goddess of the dawn, who travelled east to west announcing the Sun.