The Astronomer and the Banned Book

Bob Timmermann, Senior Librarian, History & Genealogy Department,
Central Library's Hope Street facade: sculpture of Nicholaus Copernicus
Central Library's Hope Street facade: sculpture of Nicholaus Copernicus

If you enter the Central Library on Hope Street, there are six sculptures that appear on the facade of the building. Each one stands next to a term describing the area of knowledge that the figure is supposed to exemplify. On the far right is the sculpture for “Science” and it depicts Polish astronomer, Nicholaus Copernicus. Despite being a deeply religious man (an ordained canon of the Catholic Church), Copernicus’ work would be suppressed and censored by the Catholic Church and derided as heresy by Martin Luther. His master work, De revolutionibus orbum coelestium (On the Revolutions of the Heavenly Spheres), would be one of the most famous banned books of the 17th and 18th Centuries.

Copernicus (which is a Latinized version of his original Polish name Mikolaj Kopernik) has gone down in history as the person who developed the heliocentric theory. That is, Copernicus developed a model of the solar system where the Sun was at the center and the planets revolved around it, instead of the old Aristotelean/Ptolemaic model where the Earth was at the center and everything else revolved around it.

Like many ideas in science, Copernicus’ theory was neither entirely new (ancient Greek astronomers and medieval Arab astronomers both had heliocentric models) nor widely accepted at the time it came out. Copernicus’ book was not published until either right before he died or just after his death on May 24, 1543. It is believed that he never actually saw a copy of the book that he spent the last 30 years of his life finishing. (The struggle to write this book is depicted in an interesting, and somewhat unusual way in Dava Sobel’s A More Perfect Heaven.)

On the Revolutions of the Heavenly Spheres is not an easy book to read today. The book contains numerous diagrams and has a whole lot of math in it. And since Copernicus was working in an era before calculus existed, it is even harder to understand. Also, Copernicus came up with a model of how a heliocentric solar system was laid out, but it wasn’t entirely correct. It had numerous flaws, most importantly, Copernicus believed that the orbits of all the planets around the sun were perfect circles. They aren’t.

Heliocentric model of the solar system in Copernicus' manuscript

Heliocentric model of the solar system by Copernicus.

Nevertheless, two astronomers in the 17th Century picked up on Copernicus’ work and made it popular. One was a prominent German Protestant astronomer, Johannes Kepler, who discovered that the planets made orbits that were ellipses around the sun, not perfect circles. The other was an Italian Catholic, Galileo Galilei, who used a newfangled device called the telescope, to discover that not only did the Earth rotate on its axis, but so did the other planets. And even the Sun! And not only did Earth have a Moon, but Jupiter had four of them.

Kepler managed to avoid running afoul of religious authorities as he was working under the patronage of the Holy Roman Emperors at the time. Galileo had different problems. He had to try to keep Catholic Church authorities satisfied. And during the Reformation, that wasn’t easy to do.

Galileo ran into problems when he tried to publish his new discoveries, which relied on the work of Copernicus. One of the biggest problems facing the book involved apparent conflicts with the Bible. The most notable conflict came from the Old Testament Book of Joshua, where Joshua asks God to stop the Sun in the sky so he can continue a battle that he was winning. God obliges, and Joshua and the Israelites win. (Joshua 10:13)

This was interpreted by both Catholics and Protestants at the time to mean that the Sun literally stopped in the sky. God couldn’t have stopped the Earth because if that had happened, everyone would have fallen over as if they were sitting on a giant bus that had braked suddenly.

Galileo, who was devoutly religious, believed that the Scripture in question was not to be taken literally, but it should be interpreted as an example of the miraculous nature of God’s works. This proved to be an unpopular approach with Church authorities. The majority of people who believed that Earth was at the center of the solar system didn’t believe so for religious reasons, such as God would only create a world where humans were at the center. They believed in geocentrism mostly because Aristotle said that was how things worked. And if there was one person that people in the Middle Ages and Renaissance trusted in, it was Aristotle. If you go to the Vatican, there is a fresco by Raphael called "The School of Athens" and Aristotle is one of the two central figures in it. Copernicus was afraid of taking on Aristotle, who was the epitome of conventional wisdom at the time.

With nearly all of Europe divided up into different types of Christianity, the Catholic Church, to use modern parlance, did not want its brand of Christianity to be diluted by having someone who was not a bishop or priest giving an explanation of Scripture. Galileo was told that he could talk about the heliocentric theory, but only as a hypothetical. He was told, in no uncertain terms, not to talk about it as if it were actually true.

Back in 1559, the Catholic Church had set up the Index Librorum Prohibitorum (List of Prohibited Books). A group called the Sacred Congregation of the Index was charged with identifying books that had “errors” or were heretical. Books appearing on the Index were not allowed to be published or sold in areas where the Catholic Church held authority. At times, a book could be removed from the Index if it were edited to remove any offending passages.

Index of Prohibited Books

Index Librorum prohibitorum. Courtesy of Bridwell Library, Perkins School of Theology.

The vast majority of books on the list were theological works. Copernicus’ book didn’t make the list until 1616, after Galileo had started to publicize it more in Europe. The book would not be allowed to be sold unless offending passages were removed or altered to show that the heliocentric theory was just hypothetical and not fact. And for most people in Europe, that meant you could not get the book anywhere.

Galileo would run into further trouble when he tried to bring up the issue again in the 1630s in another book, Dialog Concerning the Two Chief World Systems, Ptolemaic and Copernican. This time, the Catholic Church declared him to be a heretic, and he was forced to go to Rome and abjure (i.e., renounce) his belief in a heliocentric theory. (That turned out to be a very big deal which we don’t have the space for here. But may we suggest another book by Dava Sobel, Galileo’s Daughter?)

Copernicus remained on the Index until 1758, when Pope Benedict XIV restored the book to circulation for all Catholics. Why did he do it? Probably because by 1758, just about everyone believed in the heliocentric theory. It would have been a losing battle for the Church to tell people that they couldn’t read a book that just about every scholar in Europe agreed with. It also helped that Isaac Newton had already been around to tie up most of the loose ends on planetary motion.

The Vatican had employed astronomers and had observatories during the eras of Copernicus and Galileo. In 1891, the Vatican formally re-opened its observatory. Today, it operates pretty much like any other observatory in the world, looking for distant galaxies, searching for dark matter, and sending out cool photos.

As for the Index of Forbidden Literature, it was finally eliminated by Pope Paul VI in 1966.

Kepler’s first wife died fairly young and left him with a large family to raise. So he decided to remarry, and he lined up 11 possibilities. He wondered if there were an optimal way of going through the selections. This has turned out to be a famous math problem that has been adapted over time