What was the Carrington Event of 1859, and could it happen again?

The Carrington Event was the most intense geomagnetic storm in recorded history, peaking on 1 and 2 September 1859. It is named after Richard Carrington, one of two English astronomers, with Richard Hodgson, who independently saw a very bright flare on the Sun just before it, the first records of a solar flare. About 17.6 hours later, the storm arrived: a coronal mass ejection is thought to have covered the 150 million kilometres to Earth in that time, much faster than the several days of a typical CME.

The effects were dramatic but were those of a world with very little electrical equipment. Auroras were seen around the world, as far from the poles as Cuba, Hawaii, Queensland and even Colombia, close to the equator. In the Rocky Mountains the glow woke gold miners, who began to prepare breakfast because they thought it was morning, and in the north-eastern United States people could read a newspaper by it. Telegraph systems failed across Europe and North America, sometimes shocking their operators, and telegraph pylons threw sparks.

One of the best stories comes from the telegraph line between Boston and Portland, where the operators found they could work better without batteries. For about two hours they sent messages using only the current induced by the aurora.

Carrington himself was cautious. He suspected a link between the flare and the storm but wrote that one swallow does not make a summer. A storm of that size today has the potential to cause widespread electrical disruptions and blackouts, and damage to the power grid and satellites, which is why scientists study it.