Saw this on Wikipedia, & I thought it was good to know:

The solar storm of 1859, also known as the Solar Superstorm, or the Carrington Event, which occurred during solar cycle 10, was the most powerful solar storm in recorded history, and the largest flare, observed by Richard Christopher Carrington, became known as the Carrington Super Flare. …

From August 28, 1859, until September 2, numerous sunspots and solar flares were observed on the sun. Just before noon on September 1, the British astronomer Richard Carrington observed the largest flare, which caused a massive coronal mass ejection (CME) to travel directly toward Earth, taking 18 hours. This is remarkable because such a journey normally takes three to four days. …

Telegraph systems all over Europe and North America failed, in some cases even shocking telegraph operators. Telegraph pylons threw sparks and telegraph paper spontaneously caught fire. Some telegraph systems appeared to continue to send and receive messages despite having been disconnected from their power supplies. …

Do we need to worry about this again? Not for a while, but when it does occur…

Ice cores contain thin nitrate-rich layers that can be used to reconstruct a history of past events before reliable observations. These show evidence that events of this magnitude—as measured by high-energy proton radiation, not geomagnetic effect—occur approximately once per 500 years, with events at least one-fifth as large occurring several times per century. Less severe storms have occurred in 1921 and 1960, when widespread radio disruption was reported.

A geomagnetic storm of this sort today would cause billions of dollars of damage to satellites, power grids and radio communications, and could cause electrical blackouts on a massive scale that might not be repaired for weeks.

Gotta love Wikipedia!