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

When beggars die, there are no comets seen;

The heavens themselves blaze forth the death of princes.

Shakespeare, Julius Caesar, Act 2.2

In the winter of 1504, Christopher Columbus had a problem. He was stranded with a mutinous, hungry crew and a creaky boat in St. Anne’s Bay, Jamaica, in the midst of his fourth voyage to the New World. With their boat desperately in need of repair, the crew had beached the vessel, awaiting the return of assistance from Spain. They waited for nearly a year, but the wait was not the problem; the unruly crew was.

For much of the year, the local tribes on Jamaica had welcomed and bartered with Columbus and his men, at least until the rowdy sailors wore out their welcome. Alienated by the crew, the local tribes cut off the food supplies. The threat of mutiny, not to

mention starvation, was rising in the European camp. Columbus needed a miracle, or at least a trick, to get out of trouble.

Checking his navigational tables, the explorer found that a lunar eclipse was predicted to occur on February 29, 1504. So he arranged a meeting with the native leaders for that evening. Columbus told the tribes that his God did not care for the way the sailors were being treated. To show his displeasure, God was going to take the Moon away. The native leaders watched with interest at sunset, as the Moon rose with the reddish glow of early, partial stages of the eclipse. As the lunar disk cleared the horizon, it appeared that a chunk had been taken out of its bottom. Within the hour, the entire Moon was blotted out by Earth’s shadow.

As the story goes, the natives became terrified and offered to resume the supply of food to Columbus and his men. The explorer said he would think about it and took some time to confer with God, just enough time to return before the total eclipse ended 40-odd minutes later. God would pardon them, Columbus asserted, and bring back the Moon. And so he did. Food supplies were plentiful thereafter, and the ship’s crew was a bit more contrite, at least until the rescue ship from Europe arrived.

Columbus had no direct line to a deity, of course, but he did have a keen insight into the human mind and a decent set of reference materials. He likely had information on the Saros, the ancient mathematical formula devised by the Babylonians to predict the cycles of solar and lunar eclipses. It was probably the most valuable cargo on his ship.

For thousands of years, humans have been intrigued by the cycles in the skies, from the daily rising and setting of the Sun and stars to the monthly phases of the Moon to the yearly procession of the seasons. In the human mind, the repetition of these cycles provides a hint and hope of order in the universe. Central to that order is the idea that events in the heavens—particularly lunar and solar eclipses—can alter or portend events on Earth.

In the name of both science and soothsaying, sky watchers from Persia, Greece, China, the Middle East, the ancient Americas, and Europe spent thousands of years developing the charts to

predict future lunar and solar eclipses. Whether natural or supernatural, eclipses had an effect on civilization, and those who could predict eclipses had power in their hands. Even Stonehenge and the Medicine Wheels of the American prairies—well known as mystical calendars of the seasons—may have included mechanisms for predicting when Earth and Moon would cast their shadows on each other.

The word eclipse comes from a Greek word meaning “abandonment” or “to leave,” and for many cultures a solar eclipse was seen as the Sun abandoning the Earth. Solar eclipses happen when the new Moon passes directly between the Sun and Earth, leaving part of the Earth in the Moon’s shadow.¹ Total eclipses do not take place every time there is a new Moon because of the tilt and variation of the Moon’s orbit. On average, the Moon passes directly in front of the Sun about once a year. Conversely, during a total lunar eclipse, the full Moon passes through Earth’s shadow, and the Earth blocks all direct sunlight from the Moon.

The earliest record of a solar eclipse comes from ancient China around the year 2134 B.C.E. The ancient document Shu Ching records that “the Sun and Moon did not meet harmoniously.” Chinese folk legends of the time held that an eclipse was actually the work of an invisible dragon devouring the Sun, prompting people to make loud noise during the eclipse in order to frighten the dragon and restore daylight. According to the story, the two royal astronomers, Hsi and Ho, failed to predict the event and properly warn the people. The astronomers were promptly executed.

There is little to no mention of notable eclipses in documents from other ancient cultures, though it seems that the ancient Babylonians were the first civilization to start working out the Saros cycles, the mathematical formula of the orbital position of the Moon and Earth that calculates when eclipses will appear over some geographic area. But there was a famous eclipse recorded during the biblical era. In the eighth century B.C.E., the Hebrew prophet Amos described an eclipse in his oracles denouncing the Jewish people. He wrote: “On that day, says the Lord God, I will make the Sun set at midday and cover the Earth with darkness in

broad daylight.” Whether Amos was referring to a specific day or a more apocalyptic vision, historical and scientific records show that there was a total solar eclipse on June 15, 763 B.C.E. An Assyrian historical record known as the Eponym Canon confirms the date, and a scribe at Nineveh also recorded this eclipse.

Perhaps the most famous solar eclipse of ancient times occurred in 585 B.C.E. The Greek philosopher Thales somehow predicted a solar eclipse for May 28, 585 B.C.E., though that prediction was not widely known at the time. The eclipse occurred in the midst of a battle between the nations of Lydia and Media. Seeing the day turned into night, the startled warriors stopped fighting and agreed to a peace treaty. They cemented the bond with a double marriage among the royalty.

The mythic power of the eclipse has at times been accentuated by connections to other natural disasters and earthly events. In the apocalyptic Book of Revelation, the Gospel writer John writes: “Then I watched as he broke open the sixth seal, and there was a great earthquake; the Sun turned as black as dark sackcloth and the whole Moon became like blood.” Like Amos, John was writing symbolically, but he had tapped into an existing cultural belief— that eclipses and earthquakes are somehow linked. Years before, while writing about the Peloponnesian War, the Greek historian Thucydides noted that “earthquakes and eclipses of the Sun came to pass more frequently than had been remembered in former times.” In another passage he wrote: “There was an eclipse of the Sun at the time of a new Moon, and in the early part of the same month an earthquake.” Another Greek writer, Phlegon, reported that “in the fourth year of the two hundred second Olympiad, there was an eclipse of the Sun which was greater than any known before, and in the sixth hour of the day it became night; so that stars appeared in the heaven; and a great earthquake that broke out in Bithynia destroyed the greatest part of Nicaea.”

More than a thousand years later, John Milton wrote in the epic Paradise Lost:

Some scholars assert that Milton was alluding to Emperor Louis I, son of Charlemagne. Shortly after witnessing the eclipse of May 5, 840, Louis died. Legend holds that he was so “perplexed” by the eclipse that he died of fright. The death became historically significant because it started a struggle for succession that ended with the Treaty of Verdun, dividing the Holy Roman Empire into the three major areas we know today as France, Germany, and Italy.

Tales of great eclipses and of their ominous, wondrous, or merely coincidental effects on civilization continued right up to the era of modern science. Millions of pilgrims and tourists still trek to the “path of totality”—the swath of Earth where the Sun is totally eclipsed in any given eclipse—as they did in 1998 and 1999 to the Caribbean, Europe, and the Middle East. Grand celebrations and cultural events are planned around the days when our Sun is taken away.

Even scientists celebrate eclipses, though not just for their mythic value. To a solar physicist, an eclipse is the only natural way to see the atmosphere (chromosphere and corona) of the Sun (see Figure 4). When compared with the density of the gas and the intensity of the light on the Sun’s visible surface, or photosphere, the hot ionized gas (or plasma) of the upper atmosphere of the Sun is a million times dimmer. With the face of the Sun blocked by the Moon during a solar eclipse, the corona shines with the brightness of a full Moon. In fact, until French astronomer Bernard-Ferdinand Lyot developed a device known as a coronagraph (which uses a

FIGURE 4. Eclipses reveal the Sun’s corona, the tenuous outer atmosphere composed of streams of energetic charged particles. With the brilliant disk of the Sun blocked, the faint light of the corona reveals streamers of solar wind blowing out into space. This eclipse was photographed in 1991 from atop Mauna Kea, Hawaii. Courtesy of the High Altitude Observatory.

disk to block the visible surface of the Sun) in 1930, eclipses marked the only time anyone could see, no less study, the corona.

The view provided by an eclipse or coronagraph is important because the corona is where the action is. The Sun’s atmosphere is mysteriously millions of degrees hotter than the surface, and it is from this region that the solar wind originates, solar prominences appear and disappear, and giant bubbles of plasma—coronal mass ejections—grow and burst into the solar system. It is the corona, the tenuous atmosphere of our star, in which storms from the Sun arise.

Like eclipses, comets have inspired panic and awe since ancient times. “The celestial phenomena called comets excite wars, heated and turbulent dispositions in the atmosphere, and in the constitutions of men, with all their evil consequences,” wrote Claudius Ptolemy in the first century A.D. A Chinese silk book from the fourth century B.C.E. describes 27 types of comets and the specific calamities each produced. Aristotle wrote about comets in his Meteorologica (around 350 B.C.E.), and to the Greeks comets were known as “hairy stars.” A few hundred miles to the west, the Romans saw one of these hairy stars as a sign of the divinity of Caesar. According to Plutarch, a comet appeared around the time of Julius Caesar’s death in 44 B.C.E. Reports from China confirm a comet around that time and, 16 centuries later William Shakespeare made symbolic and poetic use of the comet in his tragic play about the Roman leader.

Many other comets have been associated with historic events. Halley’s Comet glided across the skies in A.D. 66, just a few years before the fall of Jerusalem in 70. In A.D. 79 the volcano Vesuvius erupted and destroyed the cities of Pompeii and Herculaneum while a comet trailed across the sky. The passing of the centuries did little to squelch the fear of ominous comets. A French physician, Ambroise Paré, wrote that a comet in 1528 “was so horrible, so frightful, and it produced such great terror that some died of fear and others fell sick. It appeared to be of extreme length, and was the color of blood.” In 1665 many were falling sick—the Plague was killing 90,000 people—as another great comet passed. Even during the American Civil War, the Great Comet of 1861 and comet Swift-Tuttle of 1862 were referred to as the “First and Second Civil War Comets.”

The most famous and infamous of all comets, of course, is Halley’s. Named for the English scientist who calculated its orbit and predicted its return, Halley’s comet cruises across the sky every 76 years and has historically brought trouble with it. Known to

Chinese observers since at least 240 B.C.E., it may be the first comet ever recorded (some accounts suggest it may have been recorded as far back as 1059 B.C.E). Its first famous appearance came in A.D. 1066, on the eve of the Battle of Hastings, when William the Conqueror overcame his Anglo-Saxon foes in England. That appearance of Halley’s comet was immortalized in the Bayeux tapestry. Four centuries later Pope Callixtus III excommunicated Halley’s comet as an “instrument of the devil.”

The return of Halley’s comet from September 1835 to February 1836 was perhaps the most infamous, as the comet was blamed for many things. More than 500 buildings burned in New York City during a fire that blazed for several days. Along the border of Texas and Mexico, the comet presaged the sacking of the Alamo on March 6, or was it signaling the end of the reign of General Santa Anna? In South Africa, 10,000 Zulu warriors massacred 97 Boer men and women and 185 children at Weenen. In that year, wars erupted in Cuba, Mexico, Ecuador, Central America, Peru, Argentina, and Bolivia. Osceola, chief of the Florida Seminoles, allegedly prayed to the “Big Knife in the Sky” shortly before his warriors sacked Fort King.

Not everything about the 1835 return of Halley was bad. Legendary American author Mark Twain was born the year the comet crossed the skies. Later in his life Twain was known to say that he came in with the comet and would go out when it came again. The half-baked prophecy came true when Twain died in 1910 just before Halley returned.

It was too bad that Twain passed away before he could write about the comet’s 1910 appearance, for the chicanery and foolishness surrounding the event were just the sort of tale he loved to tell. Astronomers had predicted that Earth would pass through the tail of the comet during May 1910, and some people panicked. Years earlier scientists had detected cyanogen, a poisonous gas, in the tail of a comet. That was just the opening the charlatans needed. As startled citizens spread rumors and ignorant proclamations, entrepreneurs made small fortunes selling “comet pills” that would counter the effects of the cyanogen gas that Halley would

bring. But when the Earth passed through Halley’s tail on May 20, no one died or even gasped. A few wallets were lighter.

Even as late as 1996 and 1997 comets were still ominous signs for some people. With the appearance of comets Hyakutake and Hale-Bopp, and with the apocalyptic atmosphere of the end of the millennium, comets again achieved notoriety. Supermarket tabloids suggested that Hyakutake was going to hit the Earth, and fringe cults and groups proclaimed that a UFO was trailing Hale-Bopp to take us out or to take some of us away. The hysteria culminated in the suicide of 39 members of the Heaven’s Gate cult on March 26, 1997. The group believed that an alien spacecraft was hiding in the tail of comet Hale-Bopp, ready to take them to paradise.

Whether the passage of comets actually has an impact on civi-lization—or whether humans have created their own self-fulfilling prophecies—only the theologians and psychologists can answer. But these dusty ice balls do reveal the signature of at least one natural phenomenon that affects life in the solar system: the solar wind. The solar wind is a stream of electrically charged particles— essentially, hydrogen gas that is heated to a point where it is broken into its constituent protons and electrons, or plasma.² Every minute the Sun sprays millions of tons of this plasma in all directions at 1 million miles per hour. Yet the solar wind would not ruffle the hair on your head. In the vastness of three-dimensional space, the particles become so spread out that the solar wind has less mass per cubic centimeter (density) than even the best vacuums created in laboratories on Earth. As scientists learned in the twentieth century, it is the energy and the magnetic fields carried in that tenuous solar wind that cause space weather and blow pieces of comets away as they approach the Sun.

The first indication that the Sun might be emitting a “wind” came from comet tails. Kepler in the early 1600s guessed that the pressure of sunlight created those tails, and he was mostly right. The dust tail of a comet is usually bright and white, curling slightly as the Sun vaporizes part of the head of the comet. But each comet also has a second faint tail that stretches away from the Sun. The lightly colored (usually blue) “ion” tail can accelerate suddenly

and can become distorted and kinked as super-fast streams of solar wind slough ions off of the comet. Both tails always point away from the Sun—whether the comet is inbound or outbound—as the ice and dust ball is buffeted by the outward-flowing solar wind and vaporized by the warming sunlight.

It is this solar wind—seen only in comet tails—that carries storms from the Sun to Earth. Our ancestors were not entirely wrong when they perceived some cosmic mischief at work. Comets don’t bring peril to Earth, and they don’t have much effect on life on the surface of Earth (except for those occasional collisions). But comets are shaped and affected by the Sun and the solar wind, making them more like kin than aliens.

To the dispassionate, objective viewer, auroras can appear as colorful, wispy curtains of light ruffling in the night sky. Sometimes the northern and southern lights (aurora borealis and aurora australis) stretch across the night as diffuse, flickering bands of green, blue, white, and red. Other times they streak the sky with rays or shafts of light. But for most of history, humans have seen a lot more in the heavens that just a brilliant, ghostly light show.

Aristotle, writing in his Meteorologica, made one of the first truly scientific accounts of the aurora borealis. The ancient Greek philosopher and scholar described “glowing clouds” and a light that resembled the flames of burning gas. He noted that these flames spread and at the same time sent out sparks and rays.

In Rome auroral arcs were first regarded as the mouth of a celestial cave. The Roman philosopher Seneca proposed that the auroras were flames slipping through cracks in the heavenly firmament. In A.D. 37, Emperor Tiberius saw the reddish light in the sky and thought the port of Ostia was burning. He dispatched troops to aid and rescue the inhabitants of the city, as noted by Seneca: “The cohorts hurried to the succor of the colony Ostia, believing it to be on fire. During the greater part of the night, the

heaven appears to be illuminated by a faint light resembling a thick smoke.” They marched to find nothing amiss.

Eighteen hundred years later, in 1839, all the fire brigades of London were sent north of the city to put out a fire that turned out to be an auroral blaze in the sky. A century later they were fooled again. “The ruddy glow led many to think half the city was ablaze,” the Associated Press reported from London on January 25, 1938. “The Windsor fire department was called out in the belief that Windsor Castle was afire.”

Years before Mediterranean peoples were chronicling the northern lights and Londoners were chasing them, the prophet Ezekiel may have experienced them as part of a spiritual vision. Around 593 B.C.E., during the Israelites’ exile in Babylon, he wrote: “While I was among the exiles by the river Chebar, the heavens opened and I saw divine visions. As I looked, a stormwind came from the North, a huge cloud with flashing fire from the midst of which something gleamed like electrum. Within it were figures resembling four living creatures. . . . In among the living creatures something like burning coals of fire could be seen; they seemed like torches, moving to and fro. . . . The fire gleamed, and from it came forth flashes of lightning.”

Other supernatural creatures have been spied in the dancing lights. Ancient folklore from China and Europe describe auroras, with their twisting, snake-like shapes, as great dragons or serpents in the skies. One theory holds that the dragon faced down by Britain’s patron Saint George was in fact the aurora swirling in the sky over Scotland.

In the Nordic regions of Scandinavia, Iceland, and Greenland, the aurora was often seen as the great bridge Bifrost. In Norse mythology, this burning, trembling arch was the passage for the gods—particularly Thor, the god of war—to travel from Heaven to Earth. The Finnish parallel was the river of fire, Rutja, which marked the boundary between the land of the living and the dead. Tales from the Inuit around Hudson Bay echo the Nordic bridge legends: “The sky is a huge dome of hard material arched over the flat earth. On the outside there is light. In the dome, there are a

large number of small holes, and through these holes you can see the light from the outside when it is dark. And through these holes the spirits of the dead can pass into the heavenly regions. The way to heaven leads over a narrow bridge which spans an enormous abyss. The spirits that were already in heaven light torches to guide the feet of the new arrivals. These torches are called the northern lights.” Some other Native American Indian tribes envisioned spirits carrying lanterns as they sought the souls of dead hunters, while Eskimos saw souls at play, using a walrus head as a ball. The Fox Indians of Wisconsin feared the shimmering ghosts of their dead enemies. Some Vikings envisioned the Valkyries carrying torches—or reflected light off their shields—as they led slain warriors to Valhalla.

Those who did not see supernatural beings or vigrod (“warreddening”) often interpreted the aurora as a predictor of the weather. Snow and bitter cold were often thought to follow bright auroral displays in Scandinavia, while the Eskimos saw just the opposite: the spirits were bringing favorable weather. In an attempt at a physical explanation of the aurora—and the first description to invoke the name “northern lights”—an anonymous Norwegian author took a more sober and scientific approach. The author of the Kongespeilet—“The King’s Mirror”—wrote in 1230 that: “These northern lights have this peculiar nature, that the darker the night is, the brighter they seem, and they always appear at night but never by day, most frequently in the densest darkness and rarely by moonlight. In appearance, they resemble a vast flame of fire viewed from a great distance. It also looks as if sharp points were shot from this flame up into the sky. . . . Otherwise it is the same with the northern lights as with anything else we know nothing about: that wise men put forward ideas and simple guesswork, and believe that what is most common and probable. Some people say that when the sun is under the horizon at night, some rays of light reach up to the skies over Greenland, a landmass so close to the edge of the earth that the earth’s curvature in which hides the sun must be less there.”

Some of the brightest minds in human history have puzzled over the aurora. Anders Celsius noted in his diary that volcanoes erupting near the North Pole might cause northern lights, as sulfur spewed into the atmosphere from the bowels of the Earth; later he claimed they were caused by reflected moonlight.³ Benjamin Franklin attributed the lights to a sort of lightning and electric discharge from clouds and above the atmosphere, since he thought that electricity could not enter the ice of the polar regions.

Marten Triewald even made an attempt to create artificial auroras, using a shaft of light through a darkened room, a prism, and aquavit liquor. He was a persistent promoter of the idea— also espoused by René Descartes—that auroras were caused by the refraction of moonlight by the atmosphere and the reflection of different colored rays by ice crystals. In a paper entitled “Experimentum aurorae borealis artificialis,” published in the Proceedings of the Royal Swedish Academy of Sciences, Triewald described his attempt to simulate the play of light and vapor: “One observes with wonderment a northern light so natural that nothing can be more similar, and as the surface of the aquavit is quickly warmed by the colored sunbeam and in consequence evaporates, so one perceives most wondrous movements on the screen, on which flashing beams shoot suddenly up and then transform into colored veils, endlessly changing position between themselves . . . one sees all the phenomena that the natural northern lights display and as changeable as the same . . . it is never twice the same, just like the northern light.”

We now know that the aurora is, in fact, a benign and beautiful sign that something electric is happening in the space around Earth. Named for the Roman goddess of dawn, auroras occur when fast-moving particles trapped in Earth’s magnetic field come crashing down from space into the gases of Earth’s upper atmosphere. Those electrically charged particles (electrons and protons) are governed by magnetic fields and can only move along Earth’s invisible field lines. As the solar wind pours energy into the space around Earth and energizes the magnetic field, some of the trapped

particles slide down the field lines and into the atmosphere, forming ovals of light centered on the north and south magnetic poles.

Because of the near-constant breeze of solar wind particles, auroral displays occur nearly every night in these ovals between latitude 60 and 70 degrees. (A common misconception is that auroras occur over the geographic poles. But, in fact, you would have to look south for an aurora if you were standing at the North Pole.) Nightly light shows are one of the privileges of living in the frigid extremes of Canada, Alaska, Scandinavia, Scotland, and Russia and at the far edges of New Zealand, Chile, and Antarctica.

The auroras in the northern and southern skies are quite nearly mirror reflections of each other, or “conjugates” as scientists call them. The first recorded sighting of conjugate auroras occurred in September 1770, during the expeditions of British Captain James Cook. While exploring Australia and the South Pacific on the HMS Endeavour, Joseph Banks, the crew’s naturalist, noted: “A phenomenon appeared in the heavens in many things resembling the Aurora borealis.” Later studies of the Qing-shigao, a draft history of the Qing Dynasty of China, revealed that an aurora was observed on the same night—September 16, 1770—in the northern hemisphere. As recently as October 2001, scientists gathered images of auroras occurring simultaneously in the northern and southern hemispheres, confirming that the auroral ovals mimic each other.

During more intense periods of space weather (when a coronal mass ejection or an intense flare alights from the Sun), the auroral ovals descend to lower latitudes, bringing the northern lights to such cities as Boston, Seattle, Minneapolis, or Edinburgh (about 15 to 20 times per year). Perhaps once per solar cycle the aurora can be viewed most of the way toward the equator, as it was in 1909 when the most potent magnetic storm on record brought an aurora to Singapore. These “Great Auroras” as scientists call them are the sort that inspired Norse warriors and Mediterranean philosophers, the kind that led campers in the Appalachian Mountains to believe a nuclear war had begun in March 1989. They are provoked by the severest of storms from the Sun, and for most

humans they are the only visible manifestation of a space weather event.

To the naked eye, the face of the Sun appears to be unblemished, constant, and pure. And from the time of Aristotle that was the culturally and politically correct point of view, at least in Western civilization. The heavens were perfect and unchanging, just as the gods, and then God, had made them. A spot on the Sun would mean that there is change and impurity in the heavens, and nothing could be more constant and pure than the Sun.

Yet those who watched closely, those who squinted through the thick haze or at the sunset, those who were willing to risk blindness for a peek at our star definitely saw sunspots. The oldest known records of spots on the Sun come from China in 28 B.C.E., and there is some evidence that Chinese astronomers may have seen them years before. The Greek philosopher Anaxagoras may have observed a spot in 467 B.C.E., and Theophrastus may have spied another one in the fourth century B.C.E.

But given the dominance of Aristotle’s cosmology—which was later adopted by the Catholic Church—there are few other records of any other sunspots viewed in Western civilization until the time of Galileo. Sunspots were deemed to be physically impossible, and most appearances of black splotches on the face of the Sun were explained away as planets—primarily Mercury and Venus, and the mythical planet Vulcan—passing in front of the Sun.

One of those few accounts was composed in A.D. 1128, when an English monk sketched the oldest known drawing of a sunspot. After spying a pair of sunspots on December 8, John of Worcester drew a picture of the Sun’s blemished disk and wrote: “. . . from morning to evening, appeared something like two black circles within the disk of the Sun, the one in the upper part being bigger, the other in the lower part smaller.” The fact that he could see the sunspots with the naked eye and that he could make out the umbrae and penumbrae of the spots suggest that they must have been extremely large.

Sunspots became a lot easier to see, and much harder to ignore, with the invention of the telescope in 1609. By the following year, astronomers had trained their new eyes on the Sun and began the first detailed studies. Within the course of two years, four men independently and almost simultaneously confirmed the existence of sunspots: Johannes Fabricius in Holland, Thomas Harriot in England, Galileo Galilei in Italy, and the Jesuit mathematician Christopher Scheiner in Germany. Officially, Harriot made the first observation, as recorded in his notebooks on December 8, 1610, but he did not follow those observations with any serious studies. Fabricius detected sunspots in March 1611 and quickly became the first to publish his observations. His book, De Maculis in Sole Observatis (On the Spots Observed in the Sun), was published in fall of 1611; yet none of the other three astronomers were aware of his publication for many years.

While Harriot and Fabricius recorded the official firsts, Galileo and Scheiner made the first truly scientific studies of sunspots and began to infer the physical properties of this new Sun with spots. Galileo claimed to have first seen sunspots late in 1610, but he did not actually write much about them until 1613, when he wrote the first of several responses to Scheiner’s theory that the spots were actually moons or planets with orbits very close to the Sun.

Shunning Scheiner’s interpretation—and the Church-sanctioned Aristotelian view of a perfect heaven—Galileo argued that spots were a feature of the surface or atmosphere of the Sun. He could not say what they were, but to Galileo the spots looked like clouds (see Figure 5). Ultimately, it was this assertion that the Sun had spots— combined with the discovery of Jupiter’s moons and the promotion of Copernicus’s Sun-centered view of the solar system—that led to Galileo’s excommunication from the Roman Catholic Church.

Given such a philosophical and cultural climate, extensive studies of sunspots were mostly kept in the closet until the eighteenth century. By then solar science was thriving and astronomers began keeping daily logs of the number of spots on the Sun. The first regular observations began in 1749 at the Zurich Observatory in

FIGURE 5. Galileo sketched this image of the face of the Sun on June 28, 1613. By collecting observations at about the same time each day, he and other sunspot watchers were able to decipher the motion of the spots across the solar disk. Courtesy of Owen Gingerich/Harvard-Smithsonian Center for Astrophysics.

Switzerland, and with the addition of other facilities in other parts of the world, continuous record keeping started in 1849.

An amateur astronomer, Heinrich Schwabe, was the first to turn sunspot sketches and records into a scientific advance. He studied the Sun day by day in search of the mysterious planet Vulcan, which many sky watchers believed to be the closest planet to the Sun, inside the orbit of Mercury. After 17 years of close

observation of the Sun, he noted in his “Excerpts from Solar Observations During 1843” (Astronomische Nachrichten) that there was actually a cycle, a rhythm, to the appearance of sunspots: “The weather throughout this year was so extremely favorable that I have been able to observe the Sun clearly on 312 days; however, I counted only 34 groups of sunspots. . . . From my earlier observations, it appears that there is a certain periodicity in the appearance of sunspots, and this theory seems more and more probable from the results of this year.” The number of sunspots rose and fell in a definite pattern, Schwabe noticed, over the course of his 17 years. Recalling his ill-fated search for a planet that did not exist, Schwabe said: “I may compare myself to Saul, who went to seek his father’s ass and found a kingdom.”

The initial publication of Schwabe’s work did not draw much attention. But eventually scientist and explorer Alexander von Humboldt discovered the paper. He published Schwabe’s table in his encyclopedic compilation of natural science, Cosmos. Suddenly, scientists around the world became interested in the sunspot cycle, reconstructing older records and comparing the changes in sunspot numbers with the number of magnetic storms detected on Earth. When scientists examined longer spans of solar observations, they found that the number of sunspots rose and fell in a cycle that lasted about 10 to 12 years. And by comparing 20 years of magnetic field data with Schwabe’s sunspot data, English scientist and general Edward Sabine announced in 1852 that he had found a pattern in the occurrence of magnetic storms that paralleled the rise and fall of sunspots.

Schwabe had been looking at the Sun to discover a planet inside the orbit of Mercury. Instead he discovered the most fundamentally important trait of our Sun: it is dynamic and changeable, and those changes are cyclical. It set the stage for successors to discover how changes in the appearance of the Sun produced changes on the Earth.

Bound to the Earth, our only naturally occurring experience with space weather comes from what we can see with our eyes: eclipses, comets, auroras, and sunspots. And since our vision is distorted by Earth’s atmosphere and limited to rays of visible light, it is easy to understand how we have turned eclipses and comets into divine portents and auroras and sunspots into inexplicable curiosities. When you consider that phenomena such as comets and auroras are influenced by invisible force fields (gravity and magnetic field lines) and tenuous gases of pure atomic particles (plasmas), it seems easier to believe in mythical auroral spirits, UFOs hiding behind comets, and earthquake-inducing eclipses than in space weather.

In trying to understand and explain the patterns and quirks of nature in spiritual and poetic terms, our ancestors were on to something. Eclipses, comets, auroras, and sunspots are indeed wondrous portents and signs, and the heavens really do affect life on Earth. As signals of space weather, these phenomena affect how we live in a modern technological civilization, as scientists learned firsthand in 1859.