In 1859 a geomagnetic storm from the Sun knocked out telegraph equipment in Europe and North America and sent auroras almost as far as the equator; it was the largest such event in recorded history.
The sun has seasons. Not exactly like we do, of course, but activity on the Sun’s surface fluctuates according to a very predictable cycle. It takes place over the course of eleven years. The number of sunspots, coronal mass ejections, and other solar phenomena peaks (the “solar maximum”) and then drops off (the “solar minimum”) and then rises again. And when we get to a peak, expect fireworks.
We have good records of solar activity going back to the mid-18th century. A Swiss astronomer named Rudolf Wolf used that data to create a numbering system for solar cycles. The earliest cycle for which we have solid data began in 1755; it is known as Solar Cycle 1.
(Today we’re in Solar Cycle 25 – about a year past the solar minimum, on track to hit the next solar maximum in another four years. But the most dramatic solar maximum hit more than a hundred and fifty years ago: Solar Cycle 10.
On the first day of September, 1859, two amateur British astronomers observed a huge solar flare. This, by the way, was the first time anyone actually observed a solar flare – and, as it turns out, it was a big one. The Sun had blasted out a huge belt of plasma: a coronal mass ejection. This mass shot toward the Earth, and when it hit us some seventeen hours later, it wreaked havoc.
Telegraphy was still in its infancy in 1859, but networks across Europe and North America were blasted by the sun storm’s magnetic waves. Sparks, fires, the whole system essentially ground to a halt. The so-called Carrington Event (named after one of those amateur astronomers) was the largest geomagnetic storm in recorded history.
Later geomagnetic storms would also disrupt the telegraph system, like an infamous May 1921 event, but the 1859 solar storm was an order of magnitude larger. It was so large, in fact, that the auroras usually confined to the polar regions spread far out of their usual range. Eyewitness accounts describe Northern Lights as far south as Panama and Southern Lights as far north as Australia; apparently if you were in the United States you could read in the dark by the auroras’ light.
Such a solar storm would be devastating to today’s satellites and electronics. And it’s not a question of if, it’s a question of when; during a solar maximum there are about three coronal mass ejections every day. Almost all of these miss our planet, fortunately – but not all of them.
The Generalist Academy 
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