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In 1911, a relatively unknown physicist named Albert Einstein published his preliminary theory of gravity. But it hadn’t been tested. To do that, he needed a photograph of starlight as it passed the sun during a total solar eclipse. So began a nearly decade-long quest by seven determined astronomers from observatories in four countries, who traveled the world during five eclipses to capture the elusive sight. Over the years, they faced thunderstorms, the ravages of a world war, lost equipment, and local superstitions. Finally, in May of 1919, British expeditions to northern Brazil and the island of Príncipe managed to photograph the stars, confirming Einstein’s theory.
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A PATH MADE OF MAGIC
The First Expeditions
I shall only say that I have passed a varied and eventful life, that it has been my fortune to see earth, heavens, ocean, and man in most of their aspects; but never have I beheld any spectacle which so plainly manifested the majesty of the Creator, or so forcibly taught the lesson of humility to man as a total eclipse of the sun.
—James Fenimore Cooper, “The Eclipse”
A SOLAR ECLIPSE occurs when the moon passes between the earth and the sun, totally or partially hiding the image of the sun from observers on earth.1 While our sun is four hundred times the diameter of the moon, it’s also four hundred times farther away from earth. That’s how the cosmos can perform this dramatic sleight of hand in the first place. A total solar eclipse—quite common though rarely viewed in any one place—occurs when the moon appears to cover the entire face of the sun. The moon’s shadow, or umbra, blocks all direct sunlight, turning daytime into night. Although a partial solar eclipse—its shadow is called the penumbra—is visible over a region that is thousands of miles wide, a total eclipse is observable only along a narrow path that cuts across the surface of the earth. Called the path of totality, it’s typically about 10,000 miles long, but only 50 to 100 miles wide. The chances of your house sitting in the umbra of a total eclipse are about once every 375 years.2 To witness the sun totally eclipsed by the moon, you must be standing somewhere within that slender track. And you need the luck of the draw when it comes to clear skies.
Solar eclipses figure prominently in human history. The word eclipse comes from the ancient Greek word ekleipsis, which means “being abandoned,” a rather frightening thought when you consider how important daylight and warmth were to early humans in their struggle for survival. These people had no warning, after all, let alone an explanation. Folk astronomy dates back to the early Paleolithic period, when humans formed small bands for safety and became hunters and gatherers. Solar and lunar eclipses took their place alongside other unexplainable celestial activity, such as meteor showers and lightning storms.
All over the world, myths arose about these terrifying eclipses that no one could understand. It wasn’t so many decades ago that shutters were nailed over windows during an eclipse to keep out the sun. Cattle were driven into barns for fear of them becoming blind. Pregnant women were hidden, certain foods couldn’t be eaten, candles were lit, and desperate prayers were uttered. Various cultures around the world knew what was happening, of course. Sorcerers were at work. The devil had flicked his tail between the earth and the sun. Fairies were riding on horseback, provoking the moon to steal the sun. Demons were hungry. Or perhaps it was a bear, or a frog, that needed nourishment. In many parts of the world today, folk astronomy still holds sway over science.
Records show that as early as 2500 BCE, the Babylonians and ancient Chinese were adept at predicting solar eclipses. This ability was vital since eclipses were bad omens that threatened the welfare of any ruler. The Babylonians, for example, put substitute kings on the throne, thinking they would fool the eclipse should it attempt to harm the real king. When the eclipse was over, the imposter would step down and the true ruler would again ascend the throne. In China, in particular, it was the astronomer’s job to study the skies, track solar and lunar eclipses and the movements of the planets, and then report these findings to the emperor. Because the emperor’s prosperity was at stake, these natural phenomena were so important that early astronomers might be killed if they failed to predict their occurrences.
The most famous of these stories concerns the royal astronomers Hsi and Ho. On October 22, 2134 BCE, the two became so inebriated they fell asleep and missed the solar eclipse, the oldest in recorded history. The emperor was not amused. Had they predicted the eclipse, he would have had time to form teams of his men. There would have been arrow shooters to aim at the sun and drum beaters to urge them on—an army that could fight off the invisible dragon that was devouring the sun. Of course, the sun survived anyway on that October day over four thousand years ago. Sadly, Hsi and Ho lost their heads. Although the story is apocryphal, it is said that to this day, no one has ever witnessed a drunk astronomer during an eclipse. And this verse remains as a humorous epitaph:
Here lie the bodies of Hsi and Ho,
Whose fate, though sad, was visible:
Being killed because they did not spy
the eclipse, which was invisible.
It would take centuries of eclipses before early civilizations began to see a pattern in the appearances. Because the Mesopotamians had a habit of recording events by writing them down, they first realized that eclipses didn’t just happen randomly. Although astronomy pioneers from many cultures and areas of the globe had tried for years to describe and explain them, it was not until Johannes Kepler observed a total solar eclipse, in 1605, that someone scientifically described the phenomenon. Over a hundred years later, Edmond Halley produced a map that predicted the timing and path of the May 3, 1715, eclipse. It would mark the first prediction using Newton’s theory of universal gravitation. Halley’s calculations were only four minutes and approximately eighteen miles away from being exact. Since the path of totality for this eclipse passed over London and Cambridge, Halley took the opportunity to inform the public about the nature of the phenomenon they would witness, thus advancing a lay understanding of natural science.3
Those early eclipse watchers—prehistoric, Mesopotamian, Chinese, Indian, Greek, Egyptian, Mesoamerican, Persian, and all the rest—whose solitary hard work and observations over the millennia had put in place the celestial road signs and the cosmic maps for modern times, were now mostly lost in the dust of antiquity, if their names had been recorded at all. As startling as the spectacle of totality could be, the phases were now anticipated by informed observers. In advanced parts of the world, the mystery had long been solved. Fairies were not riding on horseback. The devil had not wagged his tail. Nor had a frog eaten the sun.
AMERICA’S FIRST EXPEDITION: OCTOBER 28, 1780
Solar eclipses don’t always have good timing. America’s first official expedition was undertaken while the colonies were fighting England for independence. It was headed by Samuel Williams, third Hollis Professor at Harvard College. Science was still struggling for a foothold, despite the inroads paved by John Winthrop, considered America’s first scientist.4 At this time, colonial researchers had to deal with a public that was not sympathetic to a worldview grounded in evidence and observation. The witchcraft trials at Salem, twenty miles up the road from Harvard, were less than a century old. Superstition trumped logic in the majority of colonial homes, and science was a perceived attack on religion. But the bigger complication for this expedition was war. With the eclipse path falling over what the current map called “the east side of Longue Island”—this was Penobscot Bay in what would become the state of Maine—Williams would be traveling into enemy territory. He would need a flag of truce to travel safely.
With the help of men like Benjamin Franklin and members of the freshly formed Academy of Arts and Sciences, plans for the expedition went ahead. John Hancock wrote to the commander of the British forces, “Though we are political enemies, yet with regard to Science it is presumable we shall not dissent from the practice of all civilized people in promoting it either in conjunction or separately.”5 The British consented, but with the condition that the entourage leave the area the day after the eclipse, a demand that compelled Williams to feel “retarded and embarrassed by military orders.” The Massachusetts Board of War provided Williams with the Lincoln, an old 250-ton galley large enough to transport the passengers, crew, astronomical instruments, and food supplies he requested. The extensive list he turned over would have been coveted by George Washington, three years earlier at Valley Forge. Williams’s request included 675 gallons of wine, three dozen smoking pipes, fifty pounds of butter, and seventy-two live chickens. That he decided not to take the kitchen sink could be attributed to the fact that it had not yet been invented.
Williams and his team, which included his ten-year-old son and six of his brightest students from Harvard, were eight days at sea after leaving Boston Harbor. They were allowed to set up camp near a settler’s log house, provided they slept in his barn. And yet, this well-equipped expedition missed the track of totality on eclipse day by thirty miles. For two hundred years, American astronomers have been mystified as to why Williams made such a mistake. Was he using erroneous astronomical tables from Europe? Did his map have the wrong latitude for Penobscot Bay? After two centuries, letters written by John Davis, one of his students on the expedition, eventually surfaced to provide an answer. The British had wanted the party to stay on an island for greater security measures, denying them access to the path of totality. “Altho from the absurd policy of the military gentlemen in the neighbourhood,” Davis wrote, “we were denied the gratification of beholding that uncommon phenomenon a total eclipse of the sun, we were nevertheless favored with appearances that were new, striking, and surprising.”6
Regardless of its imperfections, this expedition was not an entire failure. For one thing, Williams described in great detail those “appearances” mentioned in the letter of 1780. They would later be known as Baily’s beads, which occur just before and after totality, when the sun is a mere crescent of light. The “beads” happen when sunlight streams through craters and other features on the moon. Edmond Halley had written of them as early as 1715, but not until astronomer Francis Baily described them in 1836 did the astronomical world pay close enough attention. Consequently, the phenomenon now bears Baily’s name. The history of discovery can be fickle and unforgiving, and it would become more so. Williams’s exploration may have been the first time that a war would interfere with an official eclipse expedition. But it wouldn’t be the last time. A more famous eclipse, coming in 1914, would greatly affect the astronomers in this story.
THE ADVENT OF THE ECLIPSE EXPEDITION
Total solar eclipses have shaped the lives of many scientists. Astronomers who happened to live within a reasonable distance from the path of totality usually traveled there, as Baily went to Scotland in 1836. Baily was an exception, an adventurer at heart having already toured extensively in America. He and George Biddell Airy, who was then astronomer royal, also observed the eclipse of July 8, 1842, in Italy. Baily set off to the Continent with a 3½-foot telescope to do his viewing at Digne-les-Bains, in southern France. When he reached Lyon and realized that he “had a few days to spare,” he changed his route to Pavia, Italy, since he had always wanted to visit Venice. He was mindful enough to follow “along the line of the moon’s shadow.”
Airy didn’t do much better planning than Baily did when he left for Turin. He had with him only a small telescope and tripod. He crossed the Alps and reached Turin on the night of July 5, less than three days before the eclipse. He turned down an offer to view it from the observatory there and decided instead on the Basilica of Superga, a structure set in the mountains eight hundred feet above the Po River. Amazingly, he didn’t start up the mountain to view his observational prospects until about two o’clock on the morning of the eclipse. He left Turin and traveled in darkness up the mountainside to arrive at the church at five that morning. These hasty methods of planning would make later astronomers cringe. But during the 1842 eclipse, Airy described on paper for the first time the phenomenon of shadow bands.
The solar eclipse on July 28, 1851, added an important milestone in eclipse history: planning and travel. It would also mark the first time that many astronomers would witness this miracle of the natural world in person. The 1851 track missed the United States altogether since Alaska was still Russian owned. It cut across northernmost Canada and then southern Greenland. It caught the northern tip of Iceland before crossing southern Norway and Sweden and then heading southeast across Poland and into the Ukraine. Some lucky astronomers of the day could stay home since the path of totality passed right over them. Before this eclipse, no properly exposed photograph of the solar corona—the most dramatic stage of an eclipse—had yet been produced. The timing of the eclipse was good as far as photography was concerned. Just a dozen years earlier, Louis Daguerre had invented a photographic process that created an image on a polished, silver-plated copper sheet sensitized with iodine vapors. This result was the daguerreotype, considered the Polaroid film of its day.
Photographing a total eclipse in those years was problematic in more ways than one. First, the great contrast between the dark shadow of the moon and the corona during totality was as much a challenge for cameras then as it still is today. Add to this the awkward angle at which the photographic equipment had to be mounted to aim at the sun, and eclipse photography became an extra challenge. Despite these drawbacks, one photographer succeeded. Hoping to get the first professional image of the corona, members of the Royal Prussian Observatory in Königsberg (now Kaliningrad, Russia) commissioned Johann Berkowski, one of the most skilled daguerreotypists in the city. Using a 2½-inch refracting telescope, Berkowski captured, in eighty-four seconds, a photograph that is still admired today as much for its beauty as for its place in eclipse history.
Several British astronomers had sailed across the North Sea to Norway and Sweden to observe the same eclipse. It rained heavily in most of Scandinavia the day before, but the sky remained cloudless on eclipse day. In the different towns, villagers had gathered out of curiosity, sitting on the grass nearby to watch these scientists whose language they did not understand. And then the moon began its slow advance on the sun. Even an experienced astronomer such as John Couch Adams, who was set up in Christiana, Norway, had never observed a total solar eclipse. He wrote of it lyrically, as though it were coming from the pen of a novice scientist:
I now quitted the telescope and looked first at the moon then around on the sky. The appearance of the corona, shining with a cold unearthly light, made an impression on my mind which can never be effaced, and an involuntary feeling of loneliness and disquietude came upon me… A party of haymakers, who had been laughing and chatting merrily at their work during the early part of the eclipse, were now seated on the ground in a group near the telescope, watching what was taking place with the greatest interest, and preserving a profound silence. A crow was the only animal near me; it seemed quite bewildered, croaking and flying backwards and forwards near the ground in an uncertain manner.
Although few astronomers had gone great distances before 1851, afterward, if they could get to India, Egypt, or a necklace of islands in the Pacific Ocean, they organized wisely. They traveled the globe when a good path of totality was predicted. They booked passage on stages, trains, and steamships. They rode on the backs of horses and donkeys. From the mid-1800s onward, they would stand on mountains or rooftops, take boats out to sea, and cross deserts and valleys. Now they were addicted. If the eclipse would not come to them, they would go to the eclipse. Academic reputations that would last a lifetime could be made at a single viewing.
WHEN AN ECLIPSE COMES TO TOWN
As the new century turned, people in all walks of life were now learning more about the moon and that blanket of stars that filled the night skies. Amateur star watchers were growing in numbers, and many were making important contributions, thanks to the encouragement from prominent astronomers at observatories in many countries. The British Astronomical Association (BAA) had formed a decade earlier for the express purpose of supporting amateurs. Turning eyes and telescopes to the skies at night is usually a solitary and quiet task. But when the most famous star of all, our sun, puts on a grand show like a total eclipse, the event tends to be a noisy affair. With seasoned astronomers now accustomed to traveling to remote areas around the globe, the setting up of a campsite became more complicated. They would need local workers and volunteers to assist them. Having a scientific expedition of prominent astronomers visit could set any small town in an uproar. For most laypeople, it would mark the most thrilling event in their lifetimes.
The century’s first total eclipse, on May 28, 1900, was a perfect example of the planning that goes into accommodating a visiting expedition. This eclipse shadow crossed the face of the earth like a current of electricity, connecting a string of human beings who waited along a path more than 10,000 miles long. Its track of totality was narrow, only 50 miles wide. But its length was expansive in that it reached many places that would provide good viewing around the globe. As the moon’s shadow moved eastward at approximately 2,200 miles per hour, it was observed by scientists in Mexico, the United States, Portugal, Spain, Algeria, Tunisia, Libya, and Egypt before it ended near the Red Sea. In the United States, its path swept across several southern states, stretching 925 miles from New Orleans to the coast of Virginia. There would not be another total eclipse viewable in the country for eighteen years, and the press jumped on it.7
Two of the towns in the southern states that lay in the eclipse path were Washington, Georgia, and Wadesboro, North Carolina. Their locations, far from city lights, would provide good sites for expeditions to set up. It was a major event in these sleepy towns when astronomers descended like locusts in 1900. They may not have been the big theatrical stars of the day, but as distinguished scientists, they were close to it. Even before the teams appeared in person, the excitement had begun. Local buildings were given fresh coats of paint. Lawns were manicured. Cafés and shops stocked up on supplies, anticipating a windfall in sales. Town committees and social groups planned afternoon teas and evening lectures for the esteemed guests. There would also be farewell picnics and barbecues when it was all over. This meant gallons of ice tea made, dozens of peach pies baked ahead, and enough skillet cornbread and barbecued pork to feed a small army.
Hotel rooms were reserved, and private residences made available to rent. Journalists and photographers arrived and found lodging. Often, the mountains of astronomical equipment would be shipped ahead, accompanied by a team member to oversee its safety. Local boys and men were then hired to unload the many railroad cars. Crates and boxes would be packed into wagons pulled by horses or mules and transported to the campsites. The folks living in the path of totality prepared as well as they could. Then they waited for the “clippers,” as they called them, to finally arrive.
A dozen of the most prestigious American observatories sent teams to these southern locations. The cast of characters would read like a who’s who of famed pioneers in the field of astronomy, both the old guard and the new. When the astronomers arrived, the serious work began. Masons would begin erecting the brick piers, and carpenters would build the wooden platforms to hold the telescopes. The canvas huts and awnings that would protect such expensive equipment from rain and sun would need erecting. Volunteers were chosen to act as security guards, standing watch at the huts during the night. Helpers who were needed on eclipse day to assist in scientific tasks such as handling the stopwatch and calling the time might be found among local merchants, blacksmiths, and farmers. They would be rehearsed in their tasks for two or three days before the eclipse. Sketch artists who could expertly capture the image of the corona either came with the expeditions or were found locally. By eclipse day, telescopes forty feet high would be pointing at the sky, like carnival rides at a state fair.
But when eccentric guests from England arrived, speaking with accents that most small-town Southerners had never heard before, the carnival coming to town was not nearly as exhilarating. Hotel chambermaids knocked on the British guests’ doors with fresh towels just to hear them speak English. One amateur member of the BAA was the Reverend J. M. Bacon, a colorful character who brought along his photographer-aerialist daughter, Gertrude. Having arrived in New York by steamer, they considered the train trip down to Wadesboro an exciting new adventure, even for the death-defying Bacons. As the train flew through the starry southern night, the reverend witnessed an explosion of glittery sparks that he believed to be a shower of meteors beyond any he had ever seen. And he would have known since he and Gertrude had once observed the Leonid shower from a hot-air balloon before they were nearly lost at sea. “I shouted this intelligence aloud that all the Pullman car might hear, meeting only with a rebuke from our dusky and amused conductor. ‘Dem are lightning bugs, Sar!’ Of course they were, but I must be held blameless for this was the first time I’d ever seen a firefly.”8
CONNECTING THE ASTRONOMERS
Nature was kind on May 28, 1900. On the day of the eclipse, there would be clear blue skies along most of the path from New Orleans to the Atlantic Ocean. The streets of Washington, Georgia, were packed tight with people, many reminding each other, “Don’t look with your bare eyes!” On out-of-the-way hilltops and in open fields, the astronomers kept close watch on the crescent’s length. Their numerous telescopes and cameras were ready. Business owners locked up shop and went with their employees into the streets. The many sketch artists, including “five young ladies from town,” stepped up to their boards, excited. Once totality began, some artists would sketch just what they saw with their naked eyes. Others would peer into the eyepieces of telescopes as they drew.
At 8:10 a.m., as the spectators waited, breathless, the moon began its ascent on the sun. As viewed in Washington, the full eclipse lasted for one minute and twenty-five seconds. That was long enough to disturb the natural world. Flocks of purple martins and swallows flew in circles overhead as cicadas and insects rattled in confusion. The Macon Telegraph commented on this disruption as the umbra fell over the countryside: “The cows that were being driven in small groups to the pastures near the city stopped in the streets and tried to turn back. Chickens and fowls cackled and cawed, denoting their alarm. The ignorant and superstitious dropped on their knees and prayed to be forgiven.” In the town of Washington, the crowd cheered wildly as the darkness receded and the sun began its reappearance.
Traveling at such a phenomenal speed, the eclipse shadow passed over South Carolina and raced on to North Carolina. The streets in Wadesboro were also flooded with spectators, an excursion train from Charlotte having arrived earlier with hundreds of people. Most of the scientists were dispersed, set up and waiting in individual encampments. Despite the early hour, the temperature was almost seventy degrees. Although the “Yanks” had been warned of the southern heat even in late May, several would collapse and need treatment by local doctors. As the full eclipse began, people watched from sidewalks or climbed to the rooftops of buildings, holding in their hands pieces of smoked glass or darkened binoculars. A smattering of small and inexpensive telescopes owned by schoolchildren were pointed at the sky. The total eclipse was over in less than ninety seconds when a sliver of yellow sun began to emerge. The shadow had already sped on to Norfolk, Virginia. There, it would dash across the Atlantic to reach the onlookers eagerly waiting in Europe and Africa.
To view the eclipse on May 28, 1900, members of the BAA were scattered along several thousand miles of the path of totality. They were almost certain that at least one group, if not many groups, would have a successful viewing. Three of the association’s members were attending the farewell picnic back in North Carolina when the eclipse reached the USS Austral, off the coast of Portugal. An amateur astronomer using nothing more than a piece of smoked glass successfully viewed the full eclipse from the ship. The shadow then made landfall and sped on to Ovar, Portugal, where William H. Christie, the astronomer royal, was waiting with his team from the Royal Observatory, Greenwich.
Many BAA members had gone to sites in Spain to view the eclipse. Astronomers had learned by now that if they could afford more than one expedition, their chances of success with the weather on eclipse day would be greater. Not all expeditions would seek out small towns, such as those in the United States. Three BAA groups had gone to the city of Algiers, one group headed by E. Walter Maunder, a chief astronomer also from the Royal Observatory. The Maunder group was checked into the Hôtel de la Régence since they would view the eclipse from its rooftop. Another BAA group in Algiers had gone to the Hôtel Continental, and a third went to the house of the British vice consul.9
On the day of the eclipse, the Maunder team members arranged themselves along the viewing side of the roof in four separate sets, for convenience. As they waited, they cleaned lenses and rubbed lamp black, the soot from oil lamps, into their cameras and telescope tubes to absorb any possible stray light. Behind them, numerous houses climbed the hillside in terraces, each rooftop filled with chattering spectators. Over at the Hôtel Continental, the same preparations were being done to ready the instruments. On the rooftop of the vice consul’s villa, the young assistants and artists got ready. They climbed up among the tall chimneys with star charts and sketch pads to wait. On the streets below, the crowd had grown to thirty thousand strong, many of them disbelievers in eclipses. They laughed and jeered as they watched the crazy English scientists, gathered like swallows on the rooftops.
- "This is a fascinating and exciting adventure tale! It chronicles the quest of eclipse-chasing astronomers who strove to test if light deflected when passing near the sun according to Einstein's theory of general relativity. Their inspiring missions depict the graceful ballet between scientific theory and experiment. In an age when we are searching for the horizons of black holes and the ripples from the origins of the universe, this book will inspire us with the ongoing excitement of understanding our cosmos."—-Walter Isaacson, author of Einstein: His Life and Universe, Benjamin Franklin: An American Life, Steve Jobs, and Leonardo da Vinci
- "With a scientist's authority and a novelist's skill, this fascinating book captures the pioneering efforts to put Einstein's theory to the test, and offers insightful portrayals of the brilliant and intrepid scientists who led the enterprise."—Martin Rees, UK Astronomer Royal and author of On the Future
"It's all there--adventure, science, history and drama--and wonderfully told."
—Michael S. Turner, cosmologist, author of The Early Universe, and inventor of the term "dark energy"
- On Sale
- Sep 24, 2019
- Page Count
- 368 pages