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The Carrington Flare

April 15, 2009
Diagram of the Flare of 1859 drawn by Richard C. Carrington. Public Domain image.

Diagram of the Flare of 1859 and associated sunspot group, drawn by Richard C. Carrington. The flare is the items labeled A-D. Public Domain image.

On September 2nd, 1859, the Earth went mad. Auroras lit up the sky over Australia, Japan, Colorado, and even as close to the equator as Venezuela. The worldwide telegraph system, which had gone from a laboratory curiosity to the wonder of the age in the previous twenty years, went haywire—sparking operators, scorching paper tapes, and mysteriously still transmitting messages between Boston, Massachusetts and Portland, Maine although the batteries that ran the system had been disconnected out of self-defense. At Kew Gardens in London, a set of magnetometers designed to study the Earth’s magnetic field started showing “disturbances of unusual violence and very wide extent” on August 27th; by September 2nd they were literally off the charts. No-one knew what was going on, with one possible exception.

Richard Carrington was an amateur solar astronomer, taking part in the last flowering of dilettante science in the decades before it became an entirely organized pursuit. He first took up astronomy with the University of Durham in 1849, but became interested specifically in the Sun after he and George Airy travelled to Sweden to view the July 28, 1851 solar eclipse (which was incidentally the first solar eclipse ever to be photographed). From then on he’d look at the stars at night, but he was devoted to solar observing.

He’d joined the University to train as an astronomer at Durham because he had an eye on doing it on his own behalf once he came into his inheritance. Carrington’s grandfather was the owner of Royal Brewery in the west of London, and was quite well-to-do. While he waited, working for the University was a cheap way to get experience. When his father took over the brewery in 1852, Carrington tapped him for a loan, resigned (with the stated reason that the poorly endowed college couldn’t afford proper equipment), and struck out on his own.

About 30 kilometers south of London in Surrey, he picked out a soggy stretch of open land not far from a railway station (the present site of the town of Redhill, though at the time just a tiny settlement called Warwick Town). There he built his own private observatory.

So equipped, Carrington was in a good position to catch an odd sight on September 1st, 1859 at 11:18 in the morning (if that seems peculiarly exact, bear in mind that the likeliest people to have precise chronometers at the time were ship’s masters and astronomers). He was engaged in his usual observation schedule, projecting the Sun onto a large darkened piece of glass and measuring sunspot positions. In particular he’d been interested in an enormous sunspot cluster north of the solar equator which had appeared on August 26th. It was large enough to be of interest to astronomers world-wide, so there is at least one photograph of it—if you’re trying to match it up with the chart above, remember that images in reflecting telescopes are inverted top to bottom.

He happened to be looking at the cluster when four bright points of light suddenly appeared from within it. He took a moment to check that the full strength of the Sun hadn’t somehow managed to come through some hole in his equipment then, satisfied that it was actually happening on the solar surface itself, called for someone to come confirm what he was seeing. As Carrington himself put it, then “on returning within 60 seconds, [he] was mortified to find that it was already much changed and enfeebled”. It disappeared entirely within a few minutes.

As it happened, a second member of the Royal Astronomical society (another Richard, this one the otherwise-obscure Richard Hodgson in London), also saw the flare and so proved conclusively that there was nothing wrong with Carrington’s equipment. By the time this was realized, though, it was already pretty clear that something truly odd had happened—something rattled the Earth’s atmosphere the next day, as described above.

The connections between light, magnetism, and electricity were still incompletely understood in 1859 (James Clerk Maxwell would not entirely coincidentally publish his tour de force on the subject over the next few years), but Michael Faraday had already discovered the Law of Induction. Shorn of mathematics, it provided for the creation of electricity if a piece of metal cuts across a magnetic field or the field instead cuts over the metal. That was the connection between the strange readings at Kew and the telegraphic events around the world. The enormous auroras were symptomatic of huge fluctuations in the Earth’s magnetic field, and those fluctuations were playing across the world’s 200,000 kilometers of telegraph wire. By analyzing the directions followed by wires and comparing them to the effects that occurred at their stations, it was even possible to develop a rough idea of how the fluctuations had flowed around the planet.

Though the correlation between sunspots and the fluctuations of Earth’s magnetic field had already been discovered by Edward Sabine, this was the first really solid evidence that the Sun could reach out to the Earth with something other than light or gravity. Conservative by nature, Carrington himself didn’t commit to a connection between his flare and the electromagnetic storm, but now we know that the Sun throws off coronal mass ejections consisting of protons and electrons (the first having been observed in 1971). We even know for sure that the 1859 event was caused by one, despite the more than a century since it occurred; protons and electrons expelled by the Sun move quickly, but not anything like the speed of light, so that accounts for the delay between Carrington seeing his flare and the beginning of the auroras.

The clincher can be found on one of the charts linked to previously. There’s a “fishhook” shape (marked with an arrow labeled “D: Solar Flare Effect”) in the bottom trace. That’s called a magnetic crochet, and it’s the characteristic bump in the Earth’s magnetic field caused by X-rays from the coronal mass ejection ionizing part of our atmosphere. X-rays move at the speed of light, outpacing the charged particles following them—and it takes eight minutes to get from the Sun to the Earth at that speed. As closely as can be told from the relatively crude instrumentation that drew the track (hours are listed at the top of the same chart), the crochet occurred within the same time frame as Carrington’s closely timed 11:18 observation of the flare. So we have both a delayed effect from the slow stream of charged particles and a high-speed effect moving at light speed; a coronal mass ejection fits the bill exactly.

Nothing like 1859’s storm has happened again, not at the same intensity anyway. There were smaller, but still extensive storms in May 1921, November 1960, and March 1989. By 1989 there were no more telegraphs, but there were electrical power lines; that last storm’s induced currents knocked out power over much of Québec by damaging transformers and electrical equipment. If something like 1859’s event were to occur today, we’d probably end up with a similar power failure across large swathes of the Northern Hemisphere, and be in the dark for a few days until enough pieces could be salvaged from the non-functional plant for use in what can be saved. Based on studies of ice cores, astronomers estimate that we only get something that size on average every 500 years or so, but it’s bit like a big earthquake—“on average” could just as easily come up tomorrow.

(With thanks to Andrew Reeves for his help tracking down source material)

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2 Comments leave one →
  1. April 15, 2009 11:55 AM

    Astronomy is actually one of the very few scientific fields that still depends crucially on amateurs. Professional astronomers have their hands full and their scopes booked solid with targeted observations planned years in advance. That leaves amateurs to keep watching the skies night after night for signs of something new.

    The Sun, though, is well-monitored by automated observatories in space; big flares are usually seen first by spacecraft such as SOHO and TRACE.

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