The "Carrington Event"

1859:

 A massive solar flare sent a cloud of charged particles that struck the Earth squarely, creating massive currents in the Earth's magnetic field and sending brilliant auroras south as far as Cuba and Hawaii. About the only thing electrical back then was the telegraph network, and the Carrington event had a literally shocking impact -- causing some operators to be shocked, and inducing strong enough currents in the telegraph wires that operators could disconnect the batteries and operate the telegraph off of the flare-induced electrical flow.

Glenn Reynolds explains how A solar flare could wipe out the communications and electrical grids while frying a wide variety of electronics, quickly sending us back to the 19th Century.