If you ask people what Galileo Galilei is famous for, most will say that he invented the telescope, used it to prove the earth goes around the sun, and that the Catholic Church condemned him for his discoveries. That much is common knowledge, no?
In fact, none of those things is true.
Galileo did not invent the telescope. When and where the telescope was invented is not certain, but what is certain is that in 1609 Galileo heard about the new invention and made one for himself. Soon he turned it on the heavens, and it was at that moment that his destiny turned to fame.
Every night brought new discoveries. He discovered that the Milky Way is not a soft band of light but a cloud of millions and millions of stars, that the moon is covered with craters, that Venus has phases like the moon, even that the sun has spots on its face. (Looking at the sun through a telescope is probably what doomed Galileo to blindness later in his life.) Excited beyond measure by his discoveries, Galileo in 1610 published a little book, Siderius Nuncius (The Starry Messenger), detailing his discoveries.
The Starry Messenger made Galileo an overnight celebrity, and his discoveries did not go unnoticed by officials of the Catholic Church, many of whom were scholarly individuals with an interest in the sciences. Some of the leading cardinals of the Church were fellow members of the scientific society to which Galileo belonged and took great interest and pride in the discoveries of their most famous member.
The Church also lauded Galileo publicly. He had a friendly audience with Pope Paul V, and in 1611 the Jesuit Roman College held a day of ceremonies to honor Galileo. When in 1614 a Dominican monk criticized Galileo from the pulpit, the leader of the Dominicans reprimanded the monk and apologized to Galileo on behalf of the entire order.
What did get Galileo into a bit of hot water with the Church was a conclusion he drew from one of his telescopic discoveries: He discovered that Jupiter has four moons that orbit around it just as the moon does the earth. He was fascinated by this, and from this and from observing the phases of Venus (which indicated that Venus orbits the sun, not the earth) he concluded that the earth goes around the sun (a view known as heliocentrism), not the sun around the earth (known as geocentrism).
Today Galileo’s conclusion seems obvious. But it was not obvious at the time, and the truth is that Galileo was jumping to conclusions unsupported by the facts. The fact that four moons orbit Jupiter does not in any way prove that the earth goes around the sun and neither does the fact that Venus shows phases as it orbits the sun.
A popular theory at the time (known as the Tychoan theory after Tycho Brahe, the famous Danish astronomer who had formulated it) proposed that all the planets orbit the sun, and the sun with its retinue of planets then orbits the earth. This theory explained Galileo’s observations quite well, and many pointed that out to Galileo. But Galileo insisted that what he had found was proof of the earth orbiting the sun. He eventually turned out to be right, but what he had at the time was not proof.
It was that lack of proof, along with his own abrasive personality, that precipitated his troubles with the Church. Galileo was known for his arrogant manner, and during his career there were a great number of people whom he had slighted, insulted, or in some way made into enemies. In 1615 some of them saw a chance to get back at Galileo by accusing him of heresy for his assertion that heliocentrism was proven fact. And so it was that the Church was prompted to inquire whether Galileo was holding views contrary to Scripture.
It must be pointed out that at the time the Church did not have an official position on whether the sun goes around the earth or vice versa. Though geocentrism was the prevailing view, both views were widely held, and it was a matter of frequent debate among the science-minded.
Indeed, most of the resistance to heliocentrism came not from the Church but from the universities. Within the Church some believed heliocentrism to be contrary to the Bible, others believed it was not. In fact, Galileo had wide support within the Church, and Jesuit astronomers were among the first to confirm his discoveries.
So when Galileo was accused of statements contrary to Scripture, the matter was referred to Cardinal Robert Bellarmine, the Church’s Master of Controversial Questions (quite a title, isn’t it?). After careful study of the matter and of Galileo’s evidence, Cardinal Bellarmine-who was later canonized and made a doctor of the Church-concluded that Galileo had not contradicted Scripture. But he did admonish Galileo not to teach that the earth moves around the sun unless he could prove it. Not an unreasonable admonition, really, but it had the effect of muzzling Galileo on the matter, because by then he realized he really did not have proof, though he still thought he was right.
And so it was that Galileo chafed under the cardinal’s admonition for most of a decade, until in 1623 the luckiest event in his life occurred: Cardinal Maffeo Barberini, a member of Galileo’s scientific society and a great fan of Galileo, became Pope Urban VIII.
This was Galileo’s dream come true: a pope who was learned in the sciences, who had not only read all of Galileo’s works but was a friend and admirer as well. Galileo was soon summoned to Rome for an audience with the Pope to discuss the latest in astronomy, and Galileo took the opportunity to ask the Pope for his blessing to write a book about the motions of the solar system.
Pope Urban VIII readily agreed to Galileo’s request, with one condition: The book must present a balanced view of both heliocentrism and geocentrism. The Pope also asked Galileo to mention the Pope’s personal view of the matter, which was that bodies in the heavens perhaps move in ways that are not understood on earth (not an unreasonable view at the time). Galileo agreed, and set forth to write his book.
Had Galileo written his book as promised there would have been no problem. But as he had many times before, Galileo was bent not only on arguing his case but on humiliating those who disagreed with him, and he wrote a book far different from what he had promised.
As was common at the time, he wrote the book in the form of a discussion among three men: one a proponent of heliocentrism, one a proponent of geocentrism, and an interested bystander. Unfortunately, the “dialogue” was one-sided-Galileo portrayed the proponent of heliocentrism as witty, intelligent, and well-informed, with the bystander often persuaded by him, while the proponent of geocentrism (whom Galileo named “Simplicius”) was portrayed as slow-witted, often caught in his own errors, and something of a dolt. This was hardly a balanced presentation of views.
But Galileo’s greatest mistake was his final twisting of the knife: He fulfilled his promise to mention the Pope’s view of the matter, but he did so by putting the Pope’s words in the mouth of the dim-witted Simplicius. This was no subtle jab-the Pope’s views were well-known, and everyone immediately realized that it was a pointed insult. This was too much for the Pope to bear. He was furious, and Galileo was summoned to Rome to explain himself.
This time things did not go well for Galileo. He was charged with a number of offenses, and though he was not imprisoned or tortured, he was shown the implements of torture. Galileo, by then an old man, was terrified, and agreed to something of a plea bargain: In return for publicly recanting his heliocentric view, he was allowed to return home with a sentence of permanent house arrest. He lived out his remaining years in his home, eventually going blind. Curiously, it was during his years of house arrest that he wrote his finest work, a book dealing with motion and inertia that is a cornerstone of modern physics.
It’s interesting to note that during all of Galileo’s conflicts with the Church, other astronomers, including the equally famous Johannes Kepler, were openly writing and teaching heliocentrism. Kepler even worked out and published the equations that describe the orbits of the planets about the sun. Yet he never had the problems Galileo did, in part because he had less to do with the Catholic Church but also because he did not have Galileo’s biting arrogance.
So it was that Galileo’s spiteful manner, his knack for turning even his best friends into enemies, repeatedly got him in trouble. His accomplishments cannot be overstated-Galileo is truly one of the giants of science-but in recounting his famous run-in with the Church, it’s also important to remember that the root of his problems were not his scientific views but his own unbridled arrogance.