A historian could best explain the arguments made in the passage regarding the pope and the clergy

By then an old man of 69 who in his defense referred to his "pitiable state of bodily indisposition," Galileo was charged with "vehement suspicion of heresy." He had to renounce "with sincere heart and unfeigned faith" his belief that the sun, not Earth, was the center of the universe and that Earth moved around the sun and not vice versa, as ecclesiastical teaching dictated.

Because he was willing to do this, at least verbally, the more serious of the threats remained only that. As one of his punishments, for example, he was to recite the seven penitential psalms once a week for three years. He also was placed under house arrest for the rest of his life.

Finally, his book, Dialogue on the Great World Systems, Ptolemaic and Copernican (1632), which lay at the heart of the trial, was added to the index of banned books, Index Librorum Prohibitorum, maintained by the Inquisition.

Ten cardinals sat in judgment of Galileo. Pope Urban VIII was not present in person, but he was there in spirit, for his personal feelings of anger and frustration were the driving force behind the extraordinary proceedings. Urban recognized just how seriously Galileo's new science challenged established church doctrine. Worse, Galileo had declared that the book of nature was written in the language of mathematics, not in biblical terms.

Cardinal Maffeo Barberini had taken the name Urban VIII in 1623 at age 55. Until then, he was, by all accounts, a warm, compassionate, intelligent human being and one of the few with whom Galileo felt that he could discuss his work intelligently.

During one of Galileo's visits to Rome soon after Urban's election, the famous scientist was granted six audiences, each lasting more than an hour, an extraordinary allocation of the pope's time. In fact, it was largely because of Urban's election that Galileo began to think he could safely write the Dialogue.

Both men had been born and raised in Florence and attended the University of Pisa, where Galileo studied medicine and Urban took a law degree. As a cardinal, Barberini had even interceded on Galileo's behalf during a confrontation with church authorities in 1616 when Galileo had been warned that his support of the concept of a sun-centered universe could bring trouble.

By 1632, about 16 years after that foreboding event, Galileo was a widely known and respected scientist and the official astronomer and philosopher at the court of the grand duke of Tuscany.

After deciding to publish the Dialogue, Galileo had followed strict protocol. He had his book scrutinized by church censors and received the church's official imprimatur. He had clearly fooled all of the officials into thinking that his ideas were being presented only as hypotheses. He had almost gotten away with publishing a heretical work without provoking papal fury.

A Loyal Son Galileo, however, was no scoffing atheist nor angry escapee from religion. He had attended Catholic school, both of his daughters had become nuns and, most important, he considered himself a loyal son of the church. He felt that he was trying to save, not hurt, the church. He was trying to prevent the church from having to defend a doctrine that he thought subject to disproof.

Galileo was far from the first to challenge authority.

In 1543, the Polish astronomer Nicolaus Copernicus had proposed the heliocentric (sun-centered) system. A canon in the Polish Catholic Church, he had recognized the possibility of trouble and delayed publication for many years. It is likely that he far overestimated the impact of his writing, which turned out to be one of history's major unread works.

As long as the doctrine lay shrouded in Latin, just another long-winded academic treatise that few read or cared about, the church could safely ignore it. The book never made the index, a sure sign of impotence -- at least not until 1616, when Galileo's support of the doctrine forced the church to recognize the fertility of Copernicus's revolutionary idea.

The traditional view had been codified about 150 A.D. by Ptolemy of Alexandria, an astronomer and geographer who put together an astronomical system to explain the apparent motion of the night sky. Ptolemy's solution was a system in which Earth was at rest in the center of the universe, with the moon, sun, planets and stars revolving around it, all embedded in a system of concentric, crystal spheres.

The advantage of Ptolemy's system was that it worked, enabling astronomers to predict with some accuracy the motions of heavenly bodies. For the calculations, Ptolemy assumed that all such bodies moved in circular paths.

To help these match observed activity, which is much more complicated, he added a set of additional smaller circular orbits called epicycles. The result was a very complex geometry, but it was the best there was.

Copernicus's idea stood Ptolemy's on its head. Copernicus considered the Ptolemaic system too complex. He hypothesized as follows: Suppose that the sun is at rest, and Earth has a twofold motion. It rotates once a day on its axis and revolves around the sun once a year.

Ptolemy and Aquinas

Copernicus was not the first to advance this heliocentric idea. Several ancient Greeks, including the astronomer Aristarchus of Samos, had proposed it about 260 B.C. Like Galileo, he was denounced for impiety but apparently unharmed. Aristarchus could advance no proof for the heliocentric idea, however, and it went into hibernation.

Ptolemy's system was the first thorough enough to deal with the observed mass of celestial motions. It matched what people "saw with their own eyes."

Later, Ptolemy's description of the universe became entrenched in Catholic Church teachings, largely through the work of Thomas Aquinas, a 13th-century theologian and philosopher. The centrality of mankind, for example, is an important part of Christian teaching and meshes nicely with an Earth-centered (geocentric) cosmology.

The Christian idea of heaven and hell also melded beautifully with the geocentric system, which saw the heavenly bodies as perfect and immutable. In other words, everything in heaven is eternal and incorruptible, whereas growth and, especially, degeneration and decay are restricted to Earth, punishment for the sins of our biblical forebears.

Astronomical references are not difficult to find in the Bible. For example, Psalm 19: "The heavens are telling the Glory of God, and the firmament proclaims his handiwork. . . . In [the heavens] he has set a tabernacle for the sun, which comes forth like a bridegroom leaving his chamber and like a strong man runs its course with joy. Its rising is from the end of the heavens and its circuit to the end of them."

What could be clearer? Also, how could Joshua have made the sun stand still if it had not been moving?

In such an atmosphere, a heliocentric universe was a jarring concept because of the implication more than the theory itself. As brave a turnabout as the Copernican theory was, it did not offer significant gain in simplicity or accuracy.

Copernicus remained hung up on the idea that the orbits of heavenly bodies must be circular because circular motion was the most "perfect" type. This fixation on circular orbits forced him to move the center of the system away from the center of the sun, where it belongs, thus depriving his system of the basic simplicity that otherwise would have been its major advantage.

Copernicus's beliefs differed from contemporary beliefs in other ways. For instance, what made the heavenly bodies move across the sky? Angels, Aquinas said. No, Copernicus said, it is in the nature of perfect circles to rotate forever.

The basic reason for his belief in his heliocentric theory also is instructive: There can be "no better place than the center for the lamp that illuminates the whole universe." It remained for Johannes Kepler, a German astronomer, physicist and mathematician, to move the heliocentric juggernaut onto the right track, mainly through his discovery that planetary orbits were elliptical, not circular.

Strangely, although Galileo and Kepler were contemporaries and had corresponded, and although Kepler was one of few other major scientists who supported the heliocentric idea, Galileo never made use of his work. Galileo, too, clung to circular orbits, indicating the difficulty of breaking an old mold.

Objections to the heliocentric theory still had to be answered. After many years of argument, Galileo finally recognized that something more substantive was needed, but he found no existing evidence that he could use.

A significant part of Galileo's evidence was based on his own observations with a telescope that he designed and built. Answering scholastics' objections that a body cannot have two simultaneous motions, he produced Jupiter's satellites, which clearly moved around Jupiter while Jupiter moved around Earth or the sun -- it really doesn't affect the argument. Dealing with the traditional claim that heavenly bodies are perfect, Galileo showed that the sun has spots and the moon has mountains.

As for the objection that Copernican doctrine required Venus to show phases, not hitherto seen, Galileo said his observations also showed Venutian phases. These sightings, however, were being made mainly in the years 1609 and 1610 through very primitive telescopes. A practiced eye was needed to make sense of them, and many of Galileo's contemporaries saw nothing but jiggling blurs of light.

Still, his Letters on the Solar Spots (1613) offered the first published statement that only the heliocentric theory fit his telescopic observations. He concluded triumphantly, "And perhaps this planet [Saturn] also, no less than horned Venus, harmonizes admirably with the great Copernican system, to the universal revelation of which doctrine propitious breezes are now seen to be directed toward us, leaving little fear of clouds or crosswinds."

Trouble was brewing in the Catholic Church, however. By 1616, Galileo was being warned by Cardinal Robert Bellarmine, an influential Jesuit theologian, that he was on dangerous ground. Bellarmine made the church's position very clear in a letter.

Commenting on a work by the Rev. Paolo Antonio Foscarini, a Carmelite who supported the Copernican system, Bellarmine wrote, "I say that, if there were a true demonstration that the sun was in the center of the universe . . . then it would be necessary to use careful consideration in explaining the Scriptures that seemed contrary. . . . But I do not think there has been any such demonstration."

Bellarmine was correct. All of Galileo's evidence, specifically the telescopic observations, showed that Earth could be revolving around the sun but did not prove that it was. If such a demonstration were available, it would shred a significant portion of church doctrine. Church authorities had felt it far better to maintain the status quo in hopes that the disturbing situation would evaporate.

Had Galileo not thought of doing the Dialogue, tension might have eased, at least for a while. The book was clever, lively and very readable. Moreover, it was in Italian rather than Latin, the choice of Copernicus, so it was widely read and discussed.

The Dialogue Its 500 pages are structured as a series of conversations over four days among three participants -- Salviati, Sagredo and Simplicio.

Salviati, named for an old friend of Galileo's who had died in 1614, speaks for Galileo. Sagredo, named in memory of another deceased friend, is the intelligent, impartial moderator, a man of high rank and of the world. Simplicio is a composite of all of Galileo's opponents.

Galileo's technique is to build his opponents' arguments through Simplicio, adding some of his own, and then to demolish those assertions with powerful arguments and often devastating satire.

Simplicio, for instance, reflects a common belief of the time that the sun, moon and stars, "which are ordained for no other use but to serve the Earth, need no other qualities for attaining that end save only those of light and motion."

"What's this?" Sagredo argues. "Will you affirm that nature has produced and designed so many vast perfect and noble celestial bodies, invariant, eternal and divine, to no other use but to serve this changeable, transitory and mortal earth? To serve that which you call the dregs of the universe and sink of all uncleanliness?"

But all of his arguments, Galileo knew, required evidence. In fact, the early part of his Dialogue is really just a softening-up operation for what Galileo feels are his devastating blows -- the evidence.

Toward the end of the book, Salviati has just explained a connection between Earth's motion and its tides. To Galileo, this is the clincher: Earth's waters move. That much is known. Through a long series of arguments, developed slowly and logically, he shows that this movement of waters is evidence that Earth does indeed move.

Sagredo breathes in wonderment: "If you had told us no more, this alone, in my judgment, so far exceeds the vanities introduced by so many others that my mere looking on them nauseates me, and I very much wonder that among men of high intelligence . . . not one has ever considered the incompatibility that is between the motion of the water contained and the immobility of the vessel containing it."

Ironically, Galileo also takes a potshot at Kepler, who had suggested that something in the heavenly bodies somehow caused tides. Kepler thought, however, that this heavenly cause was magnetism.

In the Dialogue, Salviati accuses Kepler of having "given his ear and assent to the moon's predominance over the water and to occult properties and such-like trifles." This sort of action at a distance seems to Galileo an example of Kepler's mystical bent.

Not until much later was Kepler's inspired guess borne out, for the tides indeed are caused by the moon's and, to a lesser extent, sun's gravitational (though not magnetic) pull. They are not caused by Earth's motion. This is a good example of Galileo's power with words, for even when wrong, he was convincing.

Clearly, in order to persuade readers, Galileo had to make solid, powerful arguments. To make them obvious and perhaps to vent some spleen, he used Simplicio as a foil. But the more foolish Simplicio's arguments are, the more clear is Galileo's real objective. He resolved to take this chance, and through most of the book, it works.

At the end, however, carried away perhaps by excessive zeal and secure in his conviction that he had found a way to vent without personal danger, he lets Simplicio sum up the church's position on the impossibility of obtaining true knowledge of the physical world.

Galileo's Intent If God had wanted to make Earth's waters move in a way other than by making Earth move, Simplicio says, He certainly could have done so -- "Upon which I forthwith conclude that, this being granted, it would be an extravagant boldness for anyone to limit and confine the Divine power and wisdom to one particular conjecture of his own." The "particular conjecture" to which Simplicio is referring, of course, is the Copernican system.

Simplicio's closing statement doesn't sound very explosive. It seems likely that Galileo felt the same way. Yet Galileo's enemies later convinced Urban that, if the statement came from Simplicio's mouth, Galileo's intent must have been to make fun of it and, worse, of Urban himself.

Galileo was strong-minded but not stupid. The problem was that Simplicio's assertion had been a standard papal argument and censors had directed Galileo to include it in the book. Clearly, in Galileo's thinking, the argument had to come from Simplicio. Conceivably, Galileo forgot that the argument had been Urban's.

When Urban saw the result, he was furious and unforgiving. Even after Galileo's death in 1642, Urban refused to relent. The grand duke of Tuscany, Galileo's patron for many years, wanted to hold a suitable public funeral and erect a monument over Galileo's grave at the Church of Santa Croce in Florence.

Urban warned that he would consider such action a direct insult. So the remains of one of history's great scientists were quietly hidden in the basement of the church bell tower for almost a century.

Finally, permission was given for Galileo's remains to be interred under a large monument at the church entrance, where they lie today. Nearby are the tombs of two other famous Florentines: Michelangelo and Machiavelli. The Dialogue was not released from the Index until 1822.

In fall 1980, Pope John Paul II ordered a new look at evidence in Galileo's trial. In 1992 came acquittal. But the basic conflict between established religion and modern science is still being played out.

Hal Hellman is the author of "Great Feuds in Science: Ten of the Liveliest Disputes Ever" (John Wiley & Sons, Inc., 1998), from which this article is excerpted.

© Copyright 1998 The Washington Post Company

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