The solar storm of 1859 was the most powerful solar storm in recorded history, and the largest flare; it was observed by British astronomer Richard Carrington. From August 28 to September 2 numerous sunspots and solar flares were observed on the sun.
Just before noon on September 1, Carrington observed the largest flare, which caused a massive coronal mass ejection (CME) to travel directly toward Earth, taking 17 hours. This is remarkable because such a journey normally takes three to four days. This second CME moved so quickly because the first one had cleared the way of the ambient solar wind plasma. The impact resulted in the largest geomagnetic storm ever recorded.
Aurorae were seen around the world, most notably over the Caribbean; also noteworthy were those over the Rocky Mountains that were so bright that their glow awoke gold miners, who began preparing breakfast because they thought it was morning. People who happened to be awake in the northeastern US could read a newspaper by the aurora’s light. 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.
On September 3, aurorae were reported again in Baltimore: ‘Those who happened to be out late on Thursday night had an opportunity of witnessing another magnificent display of the auroral lights. The phenomenon was very similar to the display on Sunday night, though at times the light was, if possible, more brilliant, and the prismatic hues more varied and gorgeous. The light appeared to cover the whole firmament, apparently like a luminous cloud, through which the stars of the larger magnitude indistinctly shone. The light was greater than that of the moon at its full, but had an indescribable softness and delicacy that seemed to envelop everything upon which it rested.
Between 12 and 1 o’clock, when the display was at its full brilliancy, the quiet streets of the city resting under this strange light, presented a beautiful as well as singular appearance.’ Ice cores show evidence that events of this magnitude 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.