The Day the World Discovered the Sun (32 page)

Even work done for Captain Cook that didn't succeed sometimes bred its own success. A chemist named Joseph Priestly noticed that Cook's scurvy-curing fresh vegetables and sauerkraut caused people to burp. Priestly hypothesized that perhaps liquids that caused the same reaction in a person's gut might also prevent scurvy. So he prepared apparatus to “impregnate water with fixed air” and shipped it out with Captain Cook on his second voyage. The “fixed air” (a.k.a. carbonated) beverage did not cure scurvy. But it was history's first prepared soft drink—a $370 billion industry today that makes an unlikely distant cousin to the Venus transit missions.

Jean-Baptiste Chappe d'Auteroche set in motion his own curious train of historical events. Though childless himself, Chappe's nephew Claude Chappe was so inspired by his uncle's historic voyages to Siberia and New Spain to observe the Venus transit that he devoted his life to science after reading
Voyage en Sibérie.
¹⁶
Together with his three brothers, Claude Chappe invented the visual telegraph—a grid of mechanical semaphore relay stations that from the 1790s to the 1850s constituted Europe's first ever information network. At its peak the younger Chappe's telegraph system spanned more than three thousand miles across the continent with over 556 separate stations.
¹⁷

The 1760s Venus transit voyages were also celebrated and immortalized in their day—recognized for a time as the scientific culmination of one of the Enlightenment's greatest decades. Charles Green's brother-in-law William Wales returned from his Hudson's Bay 1769 Venus
transit voyage to find a commission as Captain Cook's new astronomer on the famous mariner's second voyage. In 1775, upon completing Cook's Pacific adventures, Wales then accepted an appointment as Master of Navigation Mathematics at Christ's Hospital School in London. Wales was a popular instructor who shared tremendous stories—and posed equally tremendous mathematical problems—concerning some of the most legendary odysseys of the day. One of Wales's star pupils was a sensitive boy who spent countless hours marveling over the “wonder and mystery of the universe”—and Wales's wonderful tales of Pacific and polar adventures.

The pupil was Samuel Taylor Coleridge, whose
Rime of the Ancient Mariner
distilled all he had learned from his Venus transit voyaging teacher into skeins of gossamer verse.
¹⁸

Back in America, a theologian and Methodist minister set out to make a definitive edition of the Bible that would bring his age's greatest achievements in all fields of learning to the greatest story ever told. Adam Clarke, in his 1811 edition of the Bible, wrote a six-page footnote to Genesis 1:1, “In the beginning, God created the heavens and the Earth.”

As Clarke noted, “The word heavens must therefore comprehend the whole solar system as it is very likely the whole of this was created in these six days.” The minister then unspooled in his copious biblical footnote one and a half pages of astronomical tables (!) giving distances to sun and planets, as well as pertinent facts about the known satellites of all the planets. “The columns containing the mean distance of the planets from the sun,” Clarke continued, “are such as result from the best observations of the two last transits of Venus, which gave the solar parallax to be equal to 8 [and] three-fifths of a degree.”
¹⁹

In 1830, American educator Hervey Wilbur wrote a popular book on astronomy. Even generations after the fact, the worldwide efforts to measure the 1761 and 1769 transits still commanded a tone of reverence. “The vast importance of correct observations of a transit of Venus
is thus clearly seen,” Wilbur wrote, “as it enables man to throw his measuring line through millions of miles in space and gauge the mighty dimensions of the sun shining in his strength.”
²⁰

On June 5–6, 2012, the world will witness the final Venus transit of the twenty-first century. (Venus transits almost always come in pairs, separated by eight years. The century's other transit came on June 8, 2004.)

In North and Central America, Venus will begin to cross into the solar disk when the sun is low in the afternoon or early evening sky. The sun will have set already when the transit ends, some six-and-a-half hours later. Europe, eastern Africa, the Middle East, western Australia, and South Asia, will see the latter parts of the 2012 Venus transit as the sun rises on the morning of June 6. Japan, Indonesia, eastern China, Russia, and eastern Australia as well as Alaska, Hawaii, northwestern Canada, and islands in the Pacific Ocean will see the transit in its entirety.

These days, of course, the distance to the sun is well known—approx. 92,956,000 miles—and the value is more easily tracked and fine-tuned by radar measurements and other direct methods than by rare Venus transits. This is not to say, however, that Venus transits have ceased to be useful to astronomy.

The 2012 Venus transit may in fact help guide one field of cutting-edge science. One of the hottest research areas in astronomy is the discovery and study of “exoplanets,” planets orbiting stars other than our own. At the time of this writing, 725 exoplanets have been discovered. New ones are being added to the tally practically every week. (The website
http://exoplanet.eu
keeps the latest tabs and statistics.)

A key motivating question in exoplanet research involves estimating the number of Earth-like planets in the Milky Way capable of harboring life as we know it. (We can only study exoplanets in our galaxy and nearby satellite star clusters. Other galaxies are too far away for present-generation telescopes to be able to perform such detailed observations
of individual stars.) The first step toward an answer will be finding a bona fide “sister” Earth somewhere else in the galaxy. But once a planet closely resembling ours is found, astronomers and astrobiologists will want to know what the atmosphere around the sister Earth is like.

This is where present-day Venus transits come in handy. When Venus passes in front of the sun, the sun's light also passes through the tiny ring of Venus's atmosphere at the planet's outer edge. Astronomers routinely examine the spectrum of colors of light coming through their telescopes for hints of the distant object's composition and other characteristics. For instance, the atom hydrogen naturally gives off a red photon of light (with a wavelength of 656.3 nanometers) when its electron descends from its second excited orbital state to first excited orbital state. Tracking this “H-alpha” spectral line throughout stars and galaxies in every corner of the universe has long been a centerpiece of visual astronomy, crucially assisting the study of an object's motion, temperature, composition, age, and other properties.

Every atom and molecule has its own signature pattern of colors and spectral lines that it preferentially absorbs when light passes through it. So when Venus crosses the sun's face during a transit, the sun's light during that brief window contains tiny spectral signatures—absorption lines—emanating from Venus's atmosphere. The Venus transit, in other words, provides a rare but precious test case of an Earth-like planet with an atmosphere of known composition (thanks to Venus probes such as NASA's Venus Express and the former Soviet Union's Vega-1) as it passes in front of a well-studied star, our own.

In 2004, a team of nine French, Swiss, American, Spanish, and German astronomers observed the Venus transit, discovering not only the strong signature of carbon dioxide in the Venusian atmosphere but even the characteristic wind speeds at various altitudes above the planet's surface.
²¹
Not unlike the 1761 Venus transit, 2004 provided a proof of principle for the larger ideas that the twin transit eight years later might be able to test more fully.

In 2009, NASA launched the Kepler spacecraft, a dedicated exoplanet-finding, space-based telescope.
²²
Kepler's
raison d'être
is to perform a kind of exoplanetary stakeout, continually keeping its telescope trained on a field of 145,000 stars in the constellations Cygnus, Lyra, and Draco. It primarily looks for exoplanets transiting their host stars. Astronomers then perform follow-up studies of the candidate exoplanetary systems that Kepler finds. Using observations such as the 2004 Venus transit data as reference points, they can then examine exoplanets' atmospheres—wherever such atmospheres might be found—in finer detail. Hints of life on the exoplanet could even turn up. The presence of O
₂
, molecular oxygen, in the Earth's atmosphere certainly gives indications of lifeforms on this planet.

In December 2011, nine American and French astronomers wrote a letter to
Astronomy & Astrophysics
, a prominent journal in the field, urging their colleagues to perform careful measurements of the century's other Venus transit. “The June 2012 transit will be a unique occasion,” these scientists note, to study “a planet that was long believed to be the Earth's twin sister . . . [and] to discriminate between Earth-like and Venus-like atmospheres of exoplanets transiting their stars.”
²³

As the two eighteenth-century Venus transits enabled science to grasp its place in the universe, so the pair of twenty-first century transits help turn up clues to some of the most fundamental questions in science today: Are we alone? If not, what is life like on other worlds scattered throughout the celestial beyond?

Important note for anyone attempting to view the 2012 Venus transit:
Do not view the sun without a proper solar filter on your eyeglasses, telescope, or binoculars. Viewing the sun directly without such protection can cause permanent eye damagae, even blindness.

This book represents a homecoming of sorts. I have devoted more than a decade to researching and writing about other subjects, not the least of which was Shakespeare and Elizabethan history. It's taken a while to circle back to my original field of study, physics and astronomy. So my thanks first go to the good professors—Joel Weisberg, Bill Titus, Bruce Thomas, Cindy Blaha, William Gerace, Art Swift, Mike Skrutskie, among many—who opened up a whole universe to this undergraduate and later graduate student. Their lessons continue to inspire.

On the other hand, science is only one small part of the 1760s Venus transit story. To historians Simon Schaffer, Per Pippin Aspaas, William Sheehan, John Westfall, and Stephen Wepster as well as Cliff Thornton and Wendy Wales of the Captain Cook Society, I owe a debt of gratitude for their kind assistance and feedback during the preparation of this manuscript. A central piece of the history—the foundation of
chapters 7
,
9
, and
12
—lay buried in a manuscript for which I only had the Hungarian translation. Translating the entire document affordably and promptly into English was an odyssey all its own. (This book, not unlike the voyagers whose story it tells, followed an unforgiving timetable laid down by a forthcoming Venus transit—in this case the June 2012 transit, by which time we needed to have our book on bookstore shelves.) I am grateful for the assistance that Zsuzsa Racz, Amanda Solymosi, Roy Wright Tekastiaks, Merilee Karr, Dave Goldman, Paul Olchvary, and Stephen desJardins each provided in the search. And Ilona Dénes, the translator whom I did hire, consistently provided superb work that was prompt, careful, and professional. My special thanks to her.

This book also drew heavily on the resources generously provided by a number of research libraries and librarians. Thanks to Adam Perkins at the Cambridge University Library and to the many helpful staff at the Smith College libraries (Neilsen, Hillyer, and Young Libraries), Forbes Library (Northampton, Mass.), the Amherst College Frost Library, the
University of Massachusetts Du Bois Library, Harvard University's Widener and Houghton Libraries and Yale's Sterling Library. In the earliest stages of publicizing and promoting this book, at the time of this writing, I have also benefited from the kind assistance of Meg Thatcher, Aliza Ansell, Gerit Quealy, Max Germer, Jennifer Margulis, Kris Bordessa, Lauren Ware, Brett Paesel, and Mona Gable.

This book simply would not have existed were it not for the patient, generous, and resourceful guidance of my literary agent, Jennifer Weltz, at the Jean V. Naggar Literary Agency. Her good grace and genial humor have been a wellspring of motivation and inspiration throughout this project. I am all the more grateful that her colleagues at JVNLA—Jessica Regel, Tara Hart, Laura Biagi, Elizabeth Evans, and Alice Tasman—have contributed their tremendous talents to this project as well. My editor, Robert Pigeon, has been a steadfast and true supporter of this project from his first exposure to the idea to its final production and beyond. I extend my thanks as well to the dedicated editorial, production, promotion, and marketing teams, at Da Capo and the Perseus Books Group—including Kevin Hannover, Timm Bryson, Sean Maher, Karstin Painter, and Lara Simpson Hrabota.

This book greatly benefited from the input of readers who graciously gave of their time to critique and provide crucial feedback on early drafts of the manuscript. For their helpful critiques and insights, I remain indebted to Burl Gilyard, Joe Eskola, Megan Eskola, Sabrina Feldman, Wendy Wales, Cliff Thornton, Danielle Dart, and Kirsten Jamsen.

My friends and family—especially my father and two children—have endured more deadlines and provided more spark and light in my life than I could have hoped to ask for. To them I am forever grateful. And, finally, I owe every good word to my wife, Penny, whose love and support throughout this often supremely challenging project has never flagged. Thank you.