Auroras are created when charged solar particles slam into Earth's magnetic field and get funneled poleward. The particles collide with molecules in our atmosphere, transferring energy and making the air molecules glow.
Late last week an active region of giant sunspots—each many times larger than Earth—rotated into view.
"The active section of the sun right now is really a pretty big region, and anyone who still has whatever they watched the recent transit of Venus with would easily [spot the active area]—particularly the sunspots," said Mike Solontoi, an astronomer at the Adler Planetarium in Chicago.
Space scientists believe the sunspots flung at least two clouds of charged particles—called coronal mass ejections, or CMEs—toward Earth, setting off the intense auroral display. Northern lights were seen rippling down from the Arctic and dancing into Canada and the United States, with sightings as far south as Wisconsin, Minnesota, and Maryland.