The Day the World Discovered the Sun

An Extraordinary Story of 18th-Century Scientific Adventure

by Mark Anderson

31 May 2012

Herein are the tales of three dangerous Venus Transit voyages that risked every mortal peril—a quest that raced to an unforgettable climax, when the universe suddenly became much larger than anyone had dared to imagine.
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The Day the World Discovered the Sun: An Extraordinary Story of 18th-Century Scientific Adventure and the Global Race to Track the Transit of Venus

(Da Capo)
US: May 2012

Excerpted from Chapter One: A Star in the Sun (footnotes omitted) from The Day the World Discovered the Sun by Mark Anderson. Reprinted by arrangement with Da Capo Press, a member of the Perseus Books Group. Copyright © 2012. All rights reserved.  No part of this excerpt may be reproduced or printed without permission in writing from the publisher.

Vienna, Austria
December 31, 1760
Reddened hands fastened the barge to its mooring. For the past month the Danube’s breezes had chilled its travelers. No more. A brisk walk from the canal bank, and Vienna—with its famously narrow streets, tall buildings, and fragrant coffeehouses—welcomed its visitors in from the cold.

Just eight years before he would travel to San José del Cabo, French astronomer Jean-Baptiste Chappe d’Auteroche and his party made a wintry landing in the capital city of the Habsburg monarchy and, with it, much of the Holy Roman Empire. His was a journey altogether of its time. The turbulent 1760s—when the Enlightenment was in full bloom but before bloody revolutions had brought the age’s heady ideals down to earth—would effectively frame the world’s most concerted effort to find the sun.

In transit from Paris, Chappe and his servants—as well as “M. Durieul,” a Polish military man traveling to Warsaw—offloaded their Danube barge and walked through the city gates of Vienna. The crunching snow underfoot and clouds of condensed breath had become familiar companions as Chappe’s party daily pressed eastward. Still, the Viennese chill could not compare to the core-consuming freeze Chappe and his servants were about to undergo. Their ultimate destination was Tobolsk, a remote town in Siberia.

In April, Chappe’s colleague, the seventy-two-year-old astronomer Joseph-Nicolas Delisle, had presented a paper to the Académie Royale des Sciences in Paris arguing that Tobolsk was one of the best locations on earth to observe the coming transit of Venus on June 6, 1761. The Mappemonde that Delisle presented the French academy served as a sort of global menu of the most coveted destinations that teams of explorers and scientists across Europe would be risking their lives to venture to.

June 6 was the first time in living memory that the skies provided such a rare opportunity to plumb the solar system’s size. Venus had last transited the sun 122 years previously in 1639, more than a generation before mathematicians had figured out the trick that enabled the sun’s distance to be triangulated. Venus would provide one more chance on June 3, 1769. After that, another 105 years would elapse before Venus again passed in front of the sun.

The 1761 transit, as these scientists (known then as natural philosophers—philosophes) told their country’s paymasters, presented the best opportunity in more than a century to get a precise fix on the sun’s distance. And thanks to the planetary laws discovered by Johannes Kepler in the seventeenth century, knowing the distance to the sun allowed scientists to locate the orbital path of every planet. One measurement unrolled the blueprint to “the heavens and the earth”—what the biblical book of Genesis said God created at the universe’s very beginning. It was arguably as close to knowing the mind of the Creator as anyone had yet conceived. “If we make the best use of [the Venus transits],” the instrument maker and popular science author Benjamin Martin wrote in 1761, “there is no doubt but that astronomy will, in ten years time, attain to its ultimate perfection.”

For a seafaring nation, discovering the distance to the sun meant advancing the frontiers of knowledge intimately connected to national security. As officials from the rival British Royal Society reminded their nation’s Admiralty in a 1760 letter, Venus transit voyages required top priority attention because they constituted “the promotion of a science so intimately connected with the art of navigation as well as for the honour of the nation.”

For reasons that were scientific and geopolitical—if not also theological—Venus transit expeditions had become paramount. Even if they meant traveling to a remote and frigid location like Siberia. Although Russian scientists were already preparing their own expeditions to observe the Venus transit, the French Academy of Sciences had secured Chappe an invitation to make his own competing measurements of the celestial event at Tobolsk. Entrée to the Russian empire, with the empress’s blessing no less, spurred Chappe and his party into the Siberian beyond.

For the next eight nights, however, Chappe would enjoy a warm bed in the comfort of one of the great cosmopolitan centers of Europe. His timing was propitious. New Year’s Day in imperial Vienna was like a red-carpeted runway, providing the excuse every monied house in the city needed to strut like a peacock in full fan.

On New Year’s morning, the entire society—peasants, landed gentry, middle-class burghers, the indigent—all gathered outside the imperial Hofburg palace, where the Royal Bodyguards, ministers of state, and the city’s leading aristocratic families paraded through the square in flamboyant dress uniforms and courtly regalia. National identities in this crossroads city jockeyed for placement, with German soldiers marching first in line, followed by Polish soldiers and Hungarian troops in silvery uniforms and holstered sabers that glinted in the late morning sun.

As a visiting French dignitary, Chappe would have stayed with the French ambassador to Vienna, the Duke de Praslin—or at least enjoyed lodgings arranged by the ambassador.

When Chappe arrived, de Praslin was caught up in a particularly busy time for a diplomat. On New Year’s afternoon, families of wealth, power, and prestige gathered throughout Vienna for lavish parties that carried on well into the night. It was prime time, in other words, for a minister of state to ply and expand his network of connections.

As the afternoon shadows lengthened across the snowy streets, opulent carriages approached the city’s stately homes and paused as dandified gentlemen and bejeweled ladies alighted. For a well-educated Frenchman staying in a posh part of town, Chappe didn’t need a translator to understand the partygoers’ chatter. Public conversations in upper-class Vienna were in French, still the language of the refined and courtly set.

Inviting aromas emanating from the kitchens of the well-heeled provided an olfactory tour of Europe: chocolate from Milan, pheasant from Bohemia, fresh oysters from Istria. Enticing music also warmed the air, as Viennese nobles prided themselves in their musical sophistication—hiring some of the finest concert maestros in the world to provide entertainment. At the time, for instance, a twenty-eight-year-old composer named Franz Joseph Haydn (four years younger than Chappe) was practically reinventing the symphony as musical director for Vienna’s wealthy Morzin family.

Once the New Year revels had ended, though, life at court returned to its normal state of angst. Austria was caught up in a brutal war with Prussia—putting her conscripted soldiers through battlefield abattoirs like the battle of Torgau, in which 7,000 Austrians gave their lives in one day. France, Austria’s reluctant ally, wanted out of the coffer-draining conflagration, and Chappe’s host was already working on his new job for 1761: convince Her Majesty to consider a peace treaty with her hated rival, Prussia’s Frederick the Great.

Chappe, on the other hand, carried no such worldly baggage when he paid an invited visit to the empress and her husband, Franz I—that rare emperor who preferred to leave politics and governance to his wife. Chappe climbed the Hofburg palace stairs to the library, where the royal couple waited to receive their learned guest.

Although Maria Theresa herself had no interest in science, the emperor did. A statesman with his own intellectual passions, Franz I showed his French visitor the biggest and most comprehensive collection of rare minerals, fossils, corals, and shells in all of Europe. The emperor’s natural history cabinet—boasting 30,000 specimens collected from across the globe—even included “thunderstones” from Croatia and Bohemia. Today called meteorites, these melted miniature chunks of asteroid were at the time thought to be small pieces of earth superheated by lightning strikes.

Chappe spent his week in Vienna mingling with the great scientific researchers working there. Gerard van Swieten, personal physician to the empress, for instance, shared the latest Viennese discoveries on the use of “electricity with great success in the [treatment of] rheumatism and other disorders of the like nature,” as Chappe later recorded.

The prince of Liechtenstein entertained Chappe at Vienna’s imperial arsenal. The sixty-four-year-old Austrian military director general—who had overhauled the entire artillery, a redesign that Napoleon’s generals later copied—welcomed his French guest at a suite in the military compound. Filled with state-of-the-art cannon but missing the pungent battlefield smells of death and burnt gunpowder, the prince’s receiving room also had the air of a mini-mausoleum. Marble statues of Maria Theresa, Franz I, and Liechtenstein himself greeted the French visitor. Liechtenstein’s school of artillery science had become one of the best in the world, so Chappe perhaps made polite conversation with his host about matters relevant to the school—explosive propulsion or trajectory calculation, for instance. Chappe also recorded accepting the prince’s gift of regional fossils and local geological samples for study at his leisure.

Chappe faced the bracing January winds on a visit to the rooftop observatory at the University of Vienna. The observatory’s director was Hungarian Jesuit Maximilian Höll, who had Latinized his name as “Hell.” Father Hell showed his guest the telescope that would point at the sun on June 6—the Holy Roman Empire’s chief witness of Venus crossing the solar disk.

Hell, a lean and intent man with a piercing gaze, discussed sky and earth with his French visitor, whose pudgier frame and baby-faced visage concealed an overriding pride at least Hell’s equal. Both men of God and men of science, Hell and Chappe had as much in common as anyone Chappe would meet in Vienna. And they shared the animating passion of knowing the Creator better by better studying his creation.

Bookshelves around the observatory showcased Hell’s greatest accomplishment to date. Under his direction five years before, the observatory had begun turning out its own celestial almanacs—forecasting daily sunrise and sunset times as well as regular positions of the moon, the planets, and the moons of Jupiter. These tools enabled precision navigation anywhere on the planet and inspired great pride, even in an empire that lacked a great navy.

Chappe, whose plain dress may have lost the battle of sartorial rank, retained the upper hand throughout his meeting with Hell. As a lifelong observer of the skies, Hell knew he would find no greater career-advancing opportunity than the two upcoming Venus transits. But all Hell could do this time was go to the roof and log another day. His Viennese data would be all but irrelevant beyond the walls of his own observatory. By contrast, learned men across Europe would be eagerly awaiting posts from Chappe.

The transit’s extremes—the places on earth where Venus takes the longest and shortest length of time to cross the disk of the sun—produced some of the most valuable data for calculating the sun’s distance. According to his colleague Delisle’s all-important Mappemonde, Chappe was headed to one of the key stations on earth to observe the 1761 transit: the “Halleyan pole” where Venus would be taking the shortest time to cross the sun. “As the transit of Venus over the sun would not be performed in less time in this capital of Siberia than in any other part of the globe,” Chappe later recalled, “it could not have been viewed to so much advantage anywhere else.” Chappe’s observation promised to be one of the most important early measurements of the physical size of the solar system. The prospects of such groundbreaking science tantalized Hell: a single scientific adventure that could secure one’s own historical legacy.

Photo by Penny Leveritt

Photo by Penny Leveritt

Mark Anderson is the author of “Shakespeare” By Another Name and has covered science, history, and technology for many media outlets, including Discover and National Public Radio. He holds a BA in physics, an MS in astrophysics, and lives in western Massachusetts.

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