Galileo's Dialogue dared to discuss a forbidden topic, but that's not the only reason the book became an instant success the 17th century's equivalent of a "bestseller" when it came off the press in Florence in 1632.
The Dialogue was wonderfully well written, and its author widely known for his history-making discoveries and flamboyant style of debate.
By the time church authorities took offence at the Dialogue and moved to suppress its sales, a few months after its publication, the first edition had already sold out.
Unlike other scientific tomes of its time, which were written in Latin and addressed a scholarly audience, the Dialogue spoke in Italian to an underserved public of intelligent, curious laymen who couldn't afford a university education. Galileo's direct appeal to this mass market fanned the church's anxieties over the message his Dialogue delivered.
The book supported a stunning reversal in perception. It said the Earth was not the centre of the universe, and that the immobility of the Earth was an illusion. We spin, Galileo insisted. We speed through space. We circle the sun.
True, these same ideas had been put forward nearly a century earlier by Nicolaus Copernicus in his book, On the Revolutions of the Heavenly Spheres (1543). But only mathematicians had read Copernicus's highly technical treatise, and they kept their discussions to themselves.
No authority of the Catholic church had expressed any objection to the sun-centred cosmos of Copernicus until Galileo began endorsing it.
Galileo (1564-1642) first came to the world's attention in 1610, with the publication of his Starry Messenger, the book in which he announced mountains and valleys on the moon, four satellites orbiting the planet Jupiter and more stars studding the Milky Way than anyone had ever seen without the aid of the telescope.
Over the next few years, as he published his findings about sunspots and other surprises, Galileo spoke of his discoveries as proof for Copernicus's theory. And thanks to Galileo, Copernicus's Revolutions landed on the Index of Prohibited Books in 1616.
That silenced Galileo. Although he had been planning to write his own big book about "the construction of the universe," he judged the time too dangerous.
He put off the project for a decade, until after his most powerful admirer, Maffeo Cardinal Barberini, was elected Pope Urban VIII.
Then Galileo discussed his book idea with the new pope and got tacit permission to proceed provided he would present the two arguments equally, and not promote one side over the other.
Writing in his native Tuscan dialect (the same one Dante favoured), Galileo laced the 500-page Dialogue with grand, gorgeous language, by turns poetic, didactic, reverent, combative and funny.
He structured the book as an animated encounter among three acquaintances, spread over four days time, like a play in four acts. Each day, the men gathered and launched into a new topic: the Earth's motion, the organization of the heavenly bodies, the ebb and flow of the sea.
(Galileo thought the tides were caused by the rotation and revolution of the Earth, though in fact they are raised by the pull of the moon.)
After he finished writing his Dialogue, on Christmas Eve of 1629, Galileo sent it to Rome for examination by the censors. Several theologians scrutinized the text and gave their provisional approval.
When an outbreak of the plague interrupted the flow of communication between Rome and Florence, Galileo submitted the manuscript to new censors in his own city, so that the book went through two prepublication approval procedures.
Even so, its publication generated a shock wave that forever shattered Galileo's peace. His critics complained that he had argued the Copernican case with too much fervour. Worse, they claimed that Galileo had been ordered back in 1616 never to write about this topic, and had hidden that fact from Urban. The Pope exploded with rage, and the Inquisition summoned Galileo to Rome to stand trial.
The outcome of those infamous hearings saw Galileo publicly humiliated and the Dialogue placed on the Index.
In the summer of 1633, a lively black-market trade sprang up around the banned Dialogue, which sold for 12 times its cover price. Smuggled across the Alps and translated into Latin, the Dialogue permeated Europe in 1635. An English edition appeared in 1661.
Although the prohibition of the book by the Index endured for nearly 200 years, the original Dialogue is read with admiration in Italy today as a model of prose style.
Dava Sobel is the author of "Longitude," "Galileo's Daughter" and "The Planets." She is at work on a play about Copernicus.