What is a G5 geomagnetic storm?

(NEXSTAR) — On Friday night, the most significant G5 geomagnetic storm since 2003 hit Earth — causing several coronal mass ejections, or CMEs — and allowing many across the U.S. to see northern lights where they usually can't.

But just what does all this mean?

To start with, as explained by the weather team at Nexstar's WGN-TV in Chicago, a geomagnetic storm is "a disturbance in the Earth’s magnetosphere caused by solar wind activity." Wind from these storms can cause aurora in the sky...