Wednesday, September 09, 2015

The Solar-Powered Telegraph

The year was 1859 and, nearly six decades after the creation of Volta's battery, humans were really starting to get the hang of this electricity thing. Alternating current and low-loss power transmission lines were still a long way off, but the foundations of a communication infrastructure had emerged as telegraph cables began to crisscross the globe.

Momentous as this was, our understanding of the fundamental principles which enabled it was patchy, to say the least. Although Ampere had written his famous circuit law some thirty years earlier, it was largely through trial and error that electromagnets and relay switches were engineered to turn messages into current pulses and vice versa; it would be another two years before James Clerk Maxwell formulated laws of his own, codifying the understanding that light was an electromagnetic wave. In light of this, it’s not surprising that, when disaster struck in the Fall of that year, nobody saw it coming.

Well, that’s not precisely true. Two men saw it coming, but only in the most literal sense; Richard Carrington and Richard Hodgson, both amateur astronomers in England, were watching the sun through their telescopes on September 1st, when it belched out one of the largest solar flares in history. The flare, a massive eruption of ionized plasma now referred to as a coronal mass ejection, was pointed straight toward earth, but as the very existence of solar flares had been debated up to this point, neither man could have known what that would mean.

The coming of the solar storm was silently heralded by a pulse of high-energy x-rays, which reached the earth at about the same time as the image of the flare. This went mostly unnoticed, but a few of the era’s more sensitive magnetometers recorded the disturbance. On earth, there was relative calm, but in the interplanetary space of our solar system, a slew of charged particles screamed across the vacuum at five million miles per hour. The better part of a day later, they arrived. When they did, it was impossible not to notice.

Aurora Borealis over Bear Lake, AK
On the night-side of the planet, the sky lit up with green fire, as the northern and southern lights stretched their billowing tendrils farther from the poles than they’d ever been seen. Ordinarily, the auroras are created as the earth’s magnetosphere deflects charged particles from the sun, steering the "solar wind" around the planet and channeling it to the north and south poles, where the field lines close. But the particles from the flare were moving far too fast to be deflected, slamming into the atmosphere and creating showers of photons as they decelerated, bright enough to read by in the middle of the night.

All across the globe, telegraph lines went haywire. Some went dead, some electrocuted their operators as the immense magnetic field fluctuations created powerful currents in the wires. But two telegraph operators, one in Maine and one in Boston, discovered something amazing. In an attempt to deal with the spontaneous current that was overloading their connection, they shut off their power supplies. To their astonishment, the line stayed “open”, and they were able to continue their conversation, using only the electricity being induced in their wire by the solar storm. Long before the invention of the photovoltaic cell, they had happened upon a means of communication that was, in some sense, solar powered. It was a hard way to learn the lesson, but the Carrington flare proved what scientists had long suspected—that auroras were electromagnetic in nature—and helped us begin to see the connection between the auroras and the solar wind that powers them.

While 1859’s solar flare led to some incredible phenomena, it’s best to hope that we never see them happen again. Rudimentary as it was at the time, the telegraph system took a hard hit from the event. Modern telecom infrastructure, being infinitely more complex and correspondingly sensitive, would be completely devastated by a similar event; estimates of expected damages from such an occurrence are somewhere in the trillions for the US alone. But don’t worry, it’s not like it very nearly happened in 2012.

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