“So when did people work out that the sun was in the middle of the solar system and the earth moved around it?”
Oh, that took a while, about two thousand years from the time that the ancient Greeks decided that everything moved around the earth.
“Two thousand years?”
Not a long time in terms of the age of the universe. It wasn't that no one had suggested an alternative. Back in the time ancient Greece, Aristarchus of Samos suggested that the earth moved around the sun around 270 BC. Even before him the ancient Indian astronomers put the sun at the centre of the universe in around 900BC. A man called Nikolaus Krebs said it in the 1400’s, but it was another hundred years before the the idea really started to catch on.
“What happened then?”
A polish astronomer called Niklaus Koppernigk published a book that changed people's view of the universe for good.
“How come I've never heard of him?”
Perhaps because people usually call him by the Latin version of his name,
“I think I've heard of him. So what did he say about the universe?”
He put the Sun in the centre and then worked out a system to explain the movements of all the planets. The fancy word for this is Heliocentric and Geocentric is where the Earth is at the centre. He didn't get it exactly right but it was an important move in the right direction.
“So there must have been a big splash when he discovered that.”
Not really. Nothing happened for thirty years because he was too scared to announce it.
“Scared of what?”
The Church. At that time the Church was very powerful and totally opposed to anyone disagreeing with their view of the universe. The real problem was that he was in the Church and had the post of Canon.
“Tricky one. I can see why he looked so worried in this picture.”
So tricky that he only published his theory that placed the sun at the centre of things when he was almost on his death bed.
“So he didn’t have much time to enjoy the glory after it was published.”
True but it caused such a stir with the Church that he was probably right to wait until just before he died. Very few people actually read the book because it was banned by the Church just after its publication until 1835. By the time it could be published everyone believed the ideas anyway so no-one really bothered to read the book De Revolutionibus Orbium Coelestium which in English means On the Revolution of the Celestial Spheres. So it would probably rate as the world’s most famous and least read book.
“So how did the idea spread if the book was banned so fast?”
There is nothing like banning a book to make people seek out the few copies that were printed. One of the most important turning points was that Copernicus's ideas were taken up by greatest minds of the times, men like Galileo.
“The same man who tried to measure the speed of light with the two lamps and two assistants that you told me about earlier?”
That’s him. Galileo almost single handedly overturned the classical Greek view of the universe. Aristotle and Ptolemy represented the unquestionable truth to most people at this time. This truth required the existence of perfect, unchanging crystalline spheres, with the Earth at the centre and everything revolving in perfect circles. Galileo charged through this peaceful image of perfection like a bull in a renaissance china shop and disprove some of the most cherished ancient beliefs about the universe.
“How did he manage to do all that?”
He heard of man in Holland who had made an instrument that could far away things much clearer.
“What kind of instrument?”
A telescope. It was just a simple tube with two hand polished lenses and Galileo being good at almost everything made himself one. As soon as he did, he pointed it at the night sky. He became expert at designing telescopes and made an amazing series of discoveries about the skies above. The Greeks said the sun was this perfect glowing ball, but he discovered spots on the sun so that showed that idea was wrong. Though of course believers in the old ideas said the problem was with his telescopes.
Not at all, the Sun really does have spots but that wasn't all Galileo discovered. He found that the moon had mountains and craters that cast shadows, so the moon wasn't a perfect sphere. He found that they were far more stars than can be seen with the naked eye and the milky way, the local galaxy, is in fact made up of thousands of faint stars. He also found that Jupiter had four moons revolving around it.
“Why was that important?”
Well one of the arguments that the Earth had to be at the centre was that if it were moving through space then the moon would be left behind. So when Galileo found moons around Jupiter that removed this argument, even if the Earth did stay still how could they explain how Jupiter's moons could move with it?
“But didn't they know about gravity?”
They knew things fell if you dropped them but Isaac Newton hadn't been born yet so there was no understanding that things like the moon would be affected by gravity.
“So they accepted the idea of the Sun being at the centre of the Universe then?”
Oh they didn't give up that easily. Believers in the old established ways of thinking soon invented answers for Galileo's findings, but these were a little far fetched. Ahah, they said, yes there may appear be mountains and valleys on the moon, but the valleys are filled with a pure, transparent crystal material so the moon is really a perfect sphere.
“That's a daft idea.”
People will often jump through hoops rather than change their minds. But as the new astronomy revealed ever more about the universe, the authorities adopted a different tack. They took to the pulpits and denounced the dangerous and heretical views of these renaissance madmen. Galileo was hauled up before the ecclesiastical courts and forced to renounce his dangerously mistaken views. To save his neck he stood up and declared that the Earth remained still and everything else moved.
“Why did he change his mind?”
Oh, he didn't. In true schoolboy tradition, no sooner had he said the words than he famously muttered under his breath at the end of his trial,. ‘..but it does move’.
“So what happened to him?”
Galileo was placed under house arrest for the last years of his life but that didn't stop him writing and while he was locked up at home he produced his last book - Dialogue Concerning the Two Chief World Systems. Galileo’s book was written as conversation just like this blog. After that the idea of a telling people about science with imaginary conversations fell out of fashion for five hundred years.
“So did Galileo and Copernicus get it all right, was there anything else to discover about the movements of the planets?”
No matter how much we think we know there is always more to discover. Copernicus finally made the world believe that the Earth spun on it is axis like a top and moved around the Sun, which is quite an achievement, if you watch a sunrise or sunset it is much easier to believe the sun is really rising or falling than the ground underneath you is spinning. But he didn't get it all right, he was still attached to the ancient Greek love of circles and ended up with a very complicated system. To explain the movements of the planets the ancient Greek plan needed the planets to rotate around the Earth and do little circles in space too called epicycles. Copernicus's system was just as complicated and in fact the only thing he really got right was putting the sun at the centre of the solar system.
“Who worked out how the planets moved properly then?”
A man called Johannes Kepler who was born in 1571 in Württemberg, Germany. Worked out that the planets don't move in circles but ellipses, sort of egg shaped orbits. From this he created his three laws of planetary motion even though he didn't know why these laws were true. He just worked them from studying the movements of the planets.
“So who did that bit?”
Isaac Newton. Remember his law of gravity? Well when Newton worked out gravity it turned out that his equations could be used to show why Kepler's laws were true.
“So they got it all right?”
Not even then, there was a wobble in the planet Mercury that still couldn't be completely explained.
“So who worked that one out?”
Oh, someone not a million miles from here.