Duration and extent of the great auroral storm of 1859.

The great geomagnetic storm of August 28 through September 3, 1859 is, arguably, the greatest and most famous space weather event in the last two hundred years. For the first time observations showed that the sun and aurora were connected and that auroras generated strong ionospheric currents. A significant portion of the world's 200,000 km of telegraph lines were adversely affected, many of which were unusable for 8 h or more which had a real economic impact.