By Brad Plumer, Published: July 13 at 9:00 am
On a cool September night in 1859, campers out in Colorado were roused from sleep by a “light so bright that one could easily read common print,” as one newspaper described it. Some of them, confused, got up and began making breakfast.

Farther east, thousands of New Yorkers ran out onto their sidewalks to watch the sky glow, ribboned in yellow, white and crimson. Few people had ever seen an aurora that far south — and this one lit up the whole city.

At the time, it was a dazzling display of nature. Yet if the same thing happened today, it would be an utter catastrophe.

The auroras of 1859, known as the “Carrington Event,” came after the sun unleashed a large coronal mass ejection, a burst of charged plasma aimed directly at the Earth. When the particles hit our magnetosphere, they triggered an especially fierce geomagnetic storm that lit up the sky and frazzled communication wires around the world. Telegraphs in Philadelphia were spitting out “fantastical and unreadable messages,” one paper reported, with some systems unusable for hours.

Today, electric utilities and the insurance industry are grappling with a scary possibility. A solar storm on the scale of that in 1859 would wreak havoc on power grids, pipelines and satellites. In the worst case, it could leave 20 million to 40 million people in the Northeast without power — possibly for years — as utilities struggled to replace thousands of fried transformers stretching from Washington to Boston. Chaos and riots might ensue.

rest of the article: When space weather attacks!