In the previous post about mistakes ( Making mistakes/owning mistakes  ) I wrote that one truth about Galileo is that he asked the Church in 1616 to declare as dogma that the earth moved and the sun stood still. Cardinal Robert Bellarmine was alive at this point and had a hand in the response.  What the Church said was that no-one should discuss faith and science together.  That is, new ideas about science were to be about science. And new ideas about the sun and earth were to be discussed as theoretical not actual, until there was good evidence that they were true.

Galileo wrote a book called Dialogues Concerning The Two Chief World  Systems in which he discussed the Copernican system where the sun is at the center of the planets, and the Ptolemaic system where the earth is at the center and the sun and planets revolve around it with epicycles and flourishes. If Galileo was a pioneer in understanding the Solar System this book should be his contribution.  And yet, it isn’t.  In this book Galileo gave all sorts of reasons why the Copernican system was true and should be adopted.  For example, he was able to see phases of Venus through the telescopes he built. Copernicus had predicted that this phenomenon should exist if the Sun were truly in the center of the Solar System.  However, Copernicus himself was unable to see the phases. It took the excellent telescopes of Galileo. ** Galileo’s discovery of the moons of Jupiter aided his ideas, since here were objects that were orbiting another planet rather than the earth.

However there were two or perhaps three fatal flaws in this book. 

First Galileo believed that the double motion of the rotation and revolution of the earth could be proven by examining the tides. You can see this in his introduction to his book.  To be clear, he was saying that the existence of the tides proved that the earth was rotating. He discounted the idea that the tides were caused by the moon since no one could explain how that process worked. The Mediterranean has very small tides and they are quite chaotic compared to what you would see on the shores of the Atlantic, anywhere down the coast of Africa, or in Brazil where the Amazon responds to the tides by running backwards at its mouth for hours. In all those places the connection with the moon would be very firmly established even if it couldn’t be explained. Edmund Campion had originally charmed Queen Elizabeth by discussing tides in 1570 and even earlier, Chaucer wrote a story about an immense tide rushing inland because of a special moon.

The second mistake Galileo made was that he did not engage with the ideas of the astronomer, Tycho Brahe. Brahe was a Danish astronomer who had his own island for a planetarium and was more or less a rock star of the time. Brahe said that all the other planets circled around the sun and then, the sun and all those planets circled the earth.  Many people really liked this idea and thought it was a great compromise between what they could see for themselves and lots of new and exciting science.

To Galileo the idea was so nonsensical that he didn’t bother refuting it.  We who see this controversy from a distance of four hundred years have forgotten Brahe entirely, so we miss how important it was that Galileo didn’t even discuss Brahe in his book about world systems. But at the time the consensus was that Brahe was by far the most sensible option for people who could see that the sun rose with their own eyes.

It is also unfortunately true that in this book Galileo made fun of the Pope who until then had been a great supporter of his.

To be continued still!

** Galileo did not per se invent telescopes but he perfected them as a tool. He made his own telescopes, grinding glass blanks that he acquired from the best Venetian glass works.  The telescopes he himself built were highly prized. Princes asked for them.