Storms from the Sun: The Emerging Science of Space Weather (2002)

It is not impossible to suppose that in this case

our luminary was taken in the act . . .

Balfour Stewart

On September 1, 1859, Richard Carrington was doing what he did every day: he observed the Sun. The son of a prosperous English brewer, Carrington was more interested in astronomy than in the theology he originally set out to study. He had built his own observatory in Redhill, England, and had dedicated part of each day to observing the stars and the Sun. His research had been fruitful, as he discovered that sunspots tend to occur at different latitudes on the Sun during different stages of the Sun’s activity cycle (the cycle itself was just being uncovered by Schwabe, Sabine, and von Humboldt). By chronicling the day-to-day progress of sunspots, Carrington also found that the Sun rotates faster at the equator than it does at higher latitudes.

But at 11:18 a.m. on that late summer day in 1859, Carrington made perhaps his most compelling discovery. He had been projecting the image of the sun onto a screen—the only safe way to observe the Sun with a telescope—and sketching the sunspots as they appeared in the image. Suddenly, he noticed bright patches of white light around some of the spots in the Sun’s northern hemisphere. Thinking that his telescope or filter was allowing light to leak into the projected image, he adjusted his instrument. But the “sudden conflagration” of white blotches did not go away.

Carrington rushed from the room to get a witness, but by the time he got back, the white flash was gone. Another hour of observation left him disappointed, as the bright patch never reappeared. Months later Carrington described the event in the Monthly Notices of the Royal Astronomical Society:

Lacking a witness from his own observatory, Carrington was fortunate to find another objective observer down the road. Fellow sun watcher Richard Hodgson had observed the same conflagra-

tion from his observatory in Highgate, England. He wrote in the Monthly Notices:

What Carrington and Hodgson had witnessed was the first known sighting of a solar flare, a sudden and intense heating of the solar atmosphere comparable to an explosion. In fact, what they saw was an extremely rare “white light” flare. Most flares can only be observed in certain wavelengths with optical filters that had not yet been developed in Carrington’s day. The fact that the flare was visible in white light, against the brilliant background of the white-hot Sun, suggests that it would have been monumental even if it had not been the first one observed. By Carrington’s own accounting, the “two patches of light traversed a space of about 35,000 miles” across the face of the Sun (see Figure 6).

In the moments after the solar flare, Carrington was surprised to see that little else on the Sun had changed. “It was impossible not to expect” some change in the appearance of the spots on the Sun, he noted, but there were none. That meant that the flare must have been at least partly independent of the sunspots. “The impression left upon me is that the phenomenon took place at an elevation above the general surface of the Sun and, accordingly, altogether above and over the great group in which it was seen projected.”

But the astronomical event did not end with the flare; in fact, the pyrotechnics were just starting. While Carrington had been

FIGURE 6. Richard Carrington sketched this picture of the great white light solar flare of September 1, 1859. Note the white bands buried amid the black and gray sunspots, depicting the twin bands of the flare as it burst into view around the sunspots. Sketch from the Philosophical Transactions of the Royal Society of London.

making his observations, the magnetic instruments at the Kew Observatory in London had been recording a distortion in the magnetic field of Earth. About 18 hours later, when the blast of plasma from the Sun reached Earth, the Kew magnetometer went wild. Earth was in the throes of one of the strongest magnetic storms ever recorded—a storm that lasted more than six days and zapped the most advanced communications system of the day, the telegraph.

The X rays from the flare bombarded the Earth’s atmosphere almost instantly, cooking the ionosphere and producing a surge of electric currents. The solar flare was almost certainly accompanied by a coronal mass ejection (a phenomenon that was not actually discovered until the 1970s), a blast of hot electrified particles that sped from Sun to Earth at 2,300 kilometers per second (more than 5 million miles an hour). The shock wave and

cloud smashed into the Earth’s magnetic field, causing a huge increase in the flow of invisible electric currents in space and in our atmosphere. Those currents were strong enough to affect the strength of Earth’s magnetic field, as detected on the ground; scientists call it a magnetic storm.

In the decade leading up to Carrington’s flare, scientists such as General Edward Sabine had begun to suspect that solar activity could increase the auroral activity and could induce magnetic storms. So when Carrington learned in September 1859 that a magnetic storm had coincided with his flare, he came to suspect a physical connection between Sun and Earth. But in his notes to the Royal Astronomical Society, he qualified that connection by saying “one swallow does not make a summer.” There were too few data—just his one flare—to make such a direct connection.

Others were less cautious about the connection between Sun and Earth. Another British scientist, Balfour Stewart, spent much of 1859 through 1861 collecting anecdotes and data from scienceminded colleagues across Europe and the rest of the world. Stewart was inspired by the amazing aurora that was “observed very widely throughout our globe” and by the “magnetic disturbances of unusual violence and very wide extent.” Stewart collected magnetic field measurements from several observatories but particularly from Sabine, who had concluded seven years earlier that the pattern of magnetic storms around Earth tracked closely with the sunspot cycle. Surely the September 1 and 2 events were a direct observation and test of that geophysical connection. In a paper published in the Philosophical Transactions of the Royal Society of London, Stewart resolved to be straightforward about the link: “The interest attached to these appearances is, if possible, enhanced by the fact that at the time of their occurrence a very large spot might have been observed on the disk of our luminary—a celestial phenomenon which we have grounds for supposing to be intimately connected with auroral exhibitions and magnetic storms. . . . If no connection had been known to subsist between these two classes of phenomenon, it would, perhaps, be wrong to consider this in any other light than a casual coinci-

dence; but since General Sabine has proved that a relation exists between magnetic disturbances and sun spots, it is not impossible to suppose that in this case our luminary was taken in the act.”

Across the Atlantic, Yale University professor Elias Loomis was simultaneously studying and analyzing that link between Carrington’s sunspots, the flare, and the intense auroras on Earth. Loomis viewed the aurora from Lewiston, Maine. In the first of nearly a dozen papers he compiled on the events of September 2 for the American Journal of Science and Arts, Loomis noted that the auroral light show was “one of the most remarkable ever recorded in the United States . . . not only for the great extent of the territory over which it was observed, but also for the duration, for the intensity of illumination as well as the brilliancy of colors, and the extreme rapidity of the changes.”

The storm generated a great deal of interest in the Americas. Ordinary people had observed the unusual displays with fascination, and many recorded what they saw. Joseph Henry, the first secretary of the nascent Smithsonian Institution, published a plea asking that the flood of letters reporting the event be directed to Loomis. Seeing the event as an opportunity to tease out the mysterious physics of the aurora and of Earth’s global magnetic field, Loomis appealed to his colleagues to report the shape, duration, and variability of aurora: “It is of the highest importance to science that we should ascertain what the aurora is.” By compiling and trying to make sense of the numerous accounts from around the world, Loomis intended to get a global picture of the event. He was gathering all the facts “in the expectation that at some future day they may afford the basis for a complete and satisfactory theory” of what causes the aurora.

And the reports flooded in from all over the world. Loomis and colleagues published dozens of accounts of the great aurora of September 1859. Observers wrote of auroras visible from the usual North American outposts—Toronto, New Haven, Halifax, and West Point—and from surprised viewers in Honolulu, St. Louis, San Francisco, New Orleans, Galveston, and Key West. Daniel Kirkwood of Bloomington, Indiana wrote: “The whole visible

heavens were illuminated, the light at times being such that ordinary print could be read without much difficulty.” In the southern hemisphere, observers reported auroral lights in Santiago and Concepción, Chile, and from all over Australia. And with help from Stewart and other colleagues in Europe, Loomis acquired data and descriptions from Rome, Athens, and Russia.

The most unusual reports of auroras came from the Caribbean. Andreas Poey, director of the Physio-Meteorological Observatory at Havana, Cuba, noted: “The appearance of the aurora borealis in the twenty-third degree of latitude is so rare that it naturally produces fear in the common mind, and arrests the attention of men of science.” Though no one reported on the fears and superstitions of the common man on that night, plenty of descriptions from arrested scientific minds were filed from Puerto Rico, Jamaica, Bermuda, the Bahamas, and San Salvador. One U.S. naval officer even reported seeing the aurora from his ship off the west coast of Nicaragua.

Along with the many reports of fire in the sky, Loomis sought and received numerous reports of pyrotechnics in the telegraph offices around the world. Shortly after the first telegraph lines were established in the 1830s and 1840s, operators noticed that their systems behaved erratically when auroras were visible overhead. To send a telegraph message under normal conditions, operators manipulated and interrupted electric currents flowing through copper wires, starting and stopping with specific timings and sequences that made a code (such as Morse code). During auroral light shows, extraneous electric currents would flow through the wires, superseding the normal telegraph currents and making transmission of messages almost impossible. In one of the first scientific studies of these “spontaneous electrical currents,” W. H. Barlow wrote: “On the evening of the 19th of March, 1847, a brilliant aurora was seen, and during the whole time of its remaining visible, strong alternating deflections occurred on all the instruments. Similar effects were observed also on the telegraphs on several other lines of railway.” What Barlow and other operators did not know was that the auroral display was actually an indicator

of strong electric currents flowing through the atmosphere near Earth’s surface, playing havoc with Earth’s magnetic field and pumping geomagnetically induced current into their lines.

Such was the case in September 1859. Loomis wrote in his first report that the widespread aurora of September 2 was “equally remarkable for the disturbances which accompanied it.” Telegraph communication came to a standstill in many parts of North America and Europe. “These electrical perturbations were recorded not only by magnetic instruments, but also over the whole system of telegraph wires,” wrote Loomis. “The magnetic induction either greatly interfered with or prevented the working of the lines . . . while in more than one case [the lines worked] solely by the atmospheric influence!”

O. S. Wood, superintendent of the Canadian telegraph lines, reported that he had never witnessed anything like it in 15 years working with telegraphs. “Well-skilled operators worked incessantly . . . to get over, in even a tolerably intelligible form, about four hundred words of the steamer Indian’s report for the press; but . . . so completely were the wires under the influence of the aurora borealis that it was found utterly impossible to communicate between the telegraph stations.”

George B. Prescott, telegraph superintendent in Boston, told Loomis that the wires from Boston to Portland, Maine, were loaded with electric current all day, even though the system’s batteries were disconnected. Clever operators decided to use the mysterious currents to their own advantage. Prescott described the circumstances:

The extra current also caused some unexpected electrical hazards for telegraph operators. In a report from Springfield, Massachusetts, observers noted that flames were seen shooting from the break-key of the telegraph to the iron frame, and the “heat was sufficient to cause the smell of scorched wood and paint to be plainly perceptible.” In Washington, D.C., the smell was that of burned flesh, as telegraph operator Frederick Royce was zapped by his own equipment. “During the auroral display, I was calling Richmond and had one hand on the iron plate,” Royce explained. “Happening to lean towards the sounder, my forehead grazed a ground wire. Immediately, I received a very severe electric shock. . . . An old man who was sitting facing me said that he saw a spark of fire jump from my forehead to the sounder.”

In all, more than 70 reports were sent to the American Journal of Science and Arts, and perhaps dozens more were published or presented in Europe. The occasion of the first recorded solar flare had turned into the first widely observed instance of space weather, as the most advanced communication technology of the day had proved vulnerable to a blast from the Sun. Earlier observers had detected, individually, different aspects of the electric and magnetic connection between Sun and Earth. But never before had so many scientists and amateur observers witnessed and chronicled the flow of energy from the surface of the Sun to the surface of the Earth and into human technological systems.

“If it be true that the spots on the surface of our luminary are the primary cause of magnetic disturbances,” Balfour Stewart

wrote in the conclusion of his report on the September 1859 event, “it is to be hoped . . . that ere long something more definite may be known with regard to the exact relation between these two great phenomena.” Indeed, it would not be long.