Galileo's Vision

Four hundred years ago, the Italian scientist looked into space and changed our view of the universe

Galileo was the first to discover the moons of Jupiter. (Michael Benson / Kinetikon Pictures / Corbis (Jupiter) / Scala / Art Resource, NY (Galileo))
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In time Galileo's findings began to trouble a powerful authority—the Catholic Church. The Aristotelian worldview had been integrated with Catholic teachings, so any challenges to Aristotle had the potential to run afoul of the church. That Galileo had revealed flaws in celestial objects was bothersome enough. But some of his observations, especially the changing phases of Venus and the presence of moons around other planets, lent support to Copernicus' heliocentric theory, and that made Galileo's work potentially heretical. Biblical literalists pointed to the book of Joshua, in which the Sun is described as stopping, miraculously, "in the midst of heaven, and hasted not to go down about a whole day." How could the Sun stop if, as Copernicus and now Galileo claimed, it was already stationary? By 1614, a Dominican friar named Tommaso Caccini preached openly against Galileo, calling the Copernican worldview heretical. In 1615 another Dominican friar, Niccolò Lorini, filed a complaint against Galileo with the Roman Inquisition, a tribunal instituted the previous century to eliminate heresy.

These church challenges greatly troubled Galileo, a deeply pious man. It is a common misconception that Galileo was irreligious, but as Dava Sobel says, "Everything he did, he did as a believing Catholic." Galileo simply believed that Scripture was not intended to teach astronomy, but rather, as he wrote in a 1613 letter to his disciple Benedetto Castelli, to "persuade men of the truths necessary for salvation." Some members of the church held the same opinion: Cardinal Baronius in 1598 said that the Bible was meant "to teach us how to go to heaven, not how the heavens go."

Late in 1615, Galileo traveled to Rome to meet with church leaders personally; he was eager to present his discoveries and make the case for heliocentrism. But Baronius' view turned out to be the minority one in Rome. Galileo was cautioned against defending Copernicanism.

Eight years later, a new pope, Urban VIII, ascended and Galileo again requested permission to publish. Pope Urban granted permission—with the caveat that Galileo present the theory as a hypothesis only. But the book Galileo finally published in 1632, Dialogue Concerning the Two Chief World Systems, came off clearly in favor of the Copernican view, infuriating the pope.

And so, in what Pope John Paul II would deem, more than three centuries later, a case of "tragic mutual incomprehension," Galileo was condemned by the Holy Office of the Inquisition for being "vehemently suspected of heresy, namely of having held and believed the doctrine which is false and contrary to the Sacred and Divine Scriptures, that the Sun is the center of the world." He was sentenced to imprisonment, which was commuted to house arrest for the by then ailing 69-year-old man.

Despite repeated requests for clemency, the astronomer spent his last eight years confined to his home, forbidden to speak or write of the topics that had so captivated him. (Meanwhile, forbidden copies of his Dialogue are thought to have been widely sold on the black market.) Blindness overcame him, and as he wrote to a friend in 1638, "The universe 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."

The exact composition of some of Galileo's telescopes remains a mystery. A written fragment—a shopping list jotted on a letter—allows historians to surmise the materials Galileo used for his lenses. And so the ingredients for one of the most famous telescopes in history—an organ pipe, molds for shaping lenses, abrasives for polishing glass—are thrown in with reminders to buy soap, combs and sugar.

It's a humdrum list—as plain as the lusterless tube in a museum display. Yet what came from that tube, like the man who made it, was anything but ordinary. Galileo "was one of those who was present at the birth of modern astronomy," says Harvard-Smithsonian's Gingerich.

In the dedication of The Starry Messenger, addressed to Cosimo II, Galileo hailed the effort to "preserve from oblivion and ruin names deserving of immortality." But the moons of Jupiter he named the Medicean have come to be more commonly known as the Galilean moons, and in 1989, the spacecraft NASA launched to study them was named Galileo. And 2009 was named the International Year of Astronomy by the United Nations in honor of the 400th anniversary of Galileo's first telescopic observations.

The fame Galileo sought and obtained, he earned. "Galileo understood what was fundamentally important" about his telescopic observations, says Gingerich. "Namely, that they were showing us a whole new universe."


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