Such a small thing, really — two pieces of glass and a tube no longer than the span of a man’s arm. The first telescope that Galileo built (and I don’t mean he was the first to build one, for surely he wasn’t) played tricks with distance and size. The device transported faraway objects into the viewer’s presence, and magnified them there. As Galileo demonstrated to the Doge of Venice in 1609, even an entity invisible to the naked eye, such as an enemy ship on the horizon, would loom large within the purview of his spyglass.
Later, alone in the dark, after he’d learned how to grind better lenses, Galileo pointed his instruments skyward to reveal uncomfortable truths about the universe:
1. The supposedly smooth, silvery orb of the moon mimicked the Earth with chains of mountains and depths of valleys.
2. The familiar constellations contained more stars than anyone had counted, while the mysterious Milky Way consisted of nothing but stars, too densely packed for unaided eyes to discern.
3. The planet Jupiter commanded a retinue of four attendant bodies —“never seen since the beginning of time,” as Galileo pointed out — whose positions changed from hour to hour.
4. Venus, when followed through the telescope, waxed and waned like the moon.
5. And the large pair of companions on either side of Saturn occasionally disappeared!
This year, four centuries after those early nights of wonder, the International Year of Astronomy salutes Galileo for ushering in a new worldview. 2009 also commemorates the 400th anniversary of the publication of Astronomia Nova, by Johannes Kepler, who propounded laws of planetary motion as stunning as Galileo’s observations.
Today giant telescopes dominate mountaintops around the world, fly through space, even orbit other planets. Yet it is still possible to feel awe looking through a simple tube at the things Galileo saw. Perhaps 10 million children and adults will get that chance for themselves as they look up through IYA “Galileoscopes” and other inexpensive telescopes distributed through schools and science centers in scores of countries this year. Given the number of astronomers who recall their first glimpse of Saturn’s rings as a transformative moment, I’m betting the IYA may produce a large crop of lifelong stargazers.
Unfortunately, one of the sights that most delighted Galileo —the live view of the Milky Way — is already all but lost for most people, drowned out by the glare of urban skyglow. Understandably, therefore, an important focus of IYA activities is raising “dark skies awareness” among the 3-billion–plus city dwellers of planet Earth.
As one might expect in a multicentennial celebration year, Galileo himself is not only lionized, but also under attack as undeserving of all the attention directed at him. In England, for example, Thomas Harriot boosters are claiming that their countryman sketched the moon through a rudimentary telescope several months before Galileo did. This is true, and I hope more people will come to know and admire Harriot — not to mention the innovative Islamic astronomers of the Middle Ages and many other unsung heroes — as part of the IYA spin-off. Still, Harriot’s drawings of the moon are dimensionless renderings, whereas Galileo’s explore the play of light on a textured surface. By combining his artistic training in perspective with his mathematical skills, Galileo gauged the heights of the lunar mountains from his backyard in Padua.
Galileo’s explanations of his astounding discoveries won him admiring followers and princely rewards, but also attracted jealous enemies and zealous defenders of the faith. Even now, religious and philosophical questions that he raised reverberate — and make him the one astronomer that so many people recognize, remember something about, react to on an emotional level.
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Galileo never set out to be an astronomer. Had the telescope not distracted him from his other scientific pursuits, we would remember him today “only” as the father of experimental physics. But from the moment in his mid-40s when he first heard rumors of the instrument’s existence, he became enchanted by its possibilities. Then the sky was his oyster. In one memorable phrase from his published writings, he acknowledged his debt to God, “for being so kind as to make me alone the first observer of marvels kept hidden in obscurity for all previous centuries.”
Galileo’s discoveries convinced him that Copernicus had been right to rearrange the cosmos with the sun, instead of the Earth, at the center. He marveled at how Copernicus had come to his convictions without benefit of the telescope, and praised him publicly. As a result, Galileo took all the heat for Copernicus —who had died in 1543, as soon as his book, On the Revolutions, appeared in print. That book — a technical tome, written in Latin and dense with geometric diagrams — had not ignited the outrage of any religious censors before Galileo began touting it. But now it suddenly seemed suspect, and was listed on the Index of Prohibited Books in 1616.
Galileo’s own book on the subject, his Dialogue Concerning the Two Chief Systems of the World, came out in 1632. He wrote it in Italian rather than Latin, so that people without benefit of a university education could read about the new developments in science. You might say he was the Carl Sagan of his day. Yet the book brought him to trial before the Inquisition, and won its own place on the Index, which it occupied for nearly two centuries.
The long-standing misunderstanding between Galileo and the church led, in 1979, to a request by Pope John Paul II that the case be reopened with an eye toward reconciliation. The papal commission reviewing the Galileo affair encountered numerous difficulties, however, and the pope’s official concluding statement in 1992 fell far short of his original goal. Although it is widely held that John Paul “pardoned” Galileo, he simply regretted the “tragic mutual incomprehension” that had persisted between science and faith.
Galileo, a Catholic, accepted the Bible as the true word of God, but saw it as a book about how to go to Heaven, not how the heavens go. In other words, passages referring to the sun moving in the sky, or the Earth remaining fixed on its foundations, were never intended to teach astronomy. For that, one had to consult God’s other book — the book of Nature, which Galileo said was “written in the language of mathematics.” Galileo’s fight with the pope of his time, Urban VIII, balanced on their different attitudes toward science: Galileo insisted that inquiring minds could fathom the universe, while Urban believed the universe would never unravel itself to puny human reasoning.
Church authorities have recently been asked to weigh in on a new Galileo matter, namely the opening of his tomb in the Basilica of Santa Croce, in Florence. So far, they have denied permission to exhume, while the director of the city’s museum of the history of science persists in his request. Examining Galileo’s remains might establish the cause of his blindness, as well as confirm the identity, by DNA testing, of the female body buried with him, presumed to be the eldest of his three children.
When I first learned the terrible irony of Galileo’s blindness, I thought he had perhaps blinded himself by staring at the sun to draw its spots. But of course he was too clever to risk his eyesight that way. Instead, he had let the sunlight fall through the telescope tube onto a sheet of paper, where he safely traced the dark splotches that blemished “the very face of the sun.” The month’s worth of sunspots he drew in June and July 1612 led him to the discovery of the sun’s monthly rotation.
Galileo had complained of visual problems from an early age. No one knows whether his adolescent eye infections and miscellaneous later impairments led to the eventual loss of his sight, or whether he suffered the usual age-related insults of cataracts and glaucoma. (He was close to 80 when he died.) One of the most interesting difficulties he reported was the shimmer of colored halos around bright lights. Some historians question how his impairments may have shaped his perceptions — whether they prevented him, for example, from identifying the odd bulges at Saturn as the tips of the planet’s rings. But none of Galileo’s keenest-sighted contemporaries or immediate followers could parse that anomaly either. (The rings kept their secret another five decades before yielding to the insights and superior telescopes of Christiaan Huygens.)
Galileo, who had always been quick to announce and defend his own achievements, railed at the new darkness that enveloped him. “This universe,” he despaired in writing to a friend, “which I with my astonishing observations and clear demonstrations had enlarged a hundred, nay, a thousandfold beyond the limits commonly seen by wise men of all centuries past, is now for me so diminished and reduced, it has shrunk to the meager confines of my body.”
In his final self-assessment, Galileo appreciated that he stood at the beginning of a long process of inquiry into “recesses still deeper” that awaited “minds more piercing than my own.” Today’s astronomers find themselves standing right beside him in those sentiments, despite the progress of 400 years and a vastly extended view of our expanding universe. Information gathered by the greatest telescopes in current use suggests that all the galaxies we can see, full of bright stars and black holes, perch like mere fluff on the dominant cosmic components of dark matter and dark energy, the nature of which remains unknown.
Dava Sobel is a science writer and the author of Galileo’s Daughter, Longitude and The Planets.