Why was the earth considered the centre of our universe?
Earlier this week was ‘World Earth Day’. This got me thinking about stories that people believed for hundreds and hundreds of years about earth. Only to find out that these stories were a big fat lie. For example, Plato and Ptolemy (both ancient astronomers) wrote huge books about how the sun and the stars revolved around earth. They were much admired and respected, and so their views began to be widely considered correct. They declared the exact order in which planets and stars were fixed around earth. This order was - the Moon came first, Mercury next, Venus, sun, Mars, Jupiter and Saturn, and the stars were beyond these. According to the ancient Greeks and Egyptians (and until recently, even the Europeans) this was how they thought the universe looked like.
Before I proceed with the rest of the story about the earth being at the center and all that nonsense, I’ve got two exciting things to share -
(a) I am inviting children who like learning about flags of countries to a podcast recording - it will have some quiz questions, lots of riddles and fun-facts. If this is something you like, sign-up now!
(b) There is a fabulous podcast episode about why and how children in Finland go to school for just 5 hours a day and top the world in most competitive exams!
Back to the story on earth. Why did people believe that the earth was at the centre for over 1500 years?
To find out why, let’s pretend to get onto a time machine and travel many years back (say, into the early man’s Stone Age?). Just be careful while you’re getting out of the time-machine, for you could bump into a cave-man in a forest chasing a mammoth or a giant lion. Now that we’ve got out safely, let’s scout around for a friendly tribe and make friends with them. Let’s try a pretend conversation.
You ‘Hi Caveman, thanks for being so nice and friendly. I loved the carrots you gave me for dinner. I was wondering if I could have a banana tomorrow morning? By morning, I mean when the sun rises and the earth begins to spin around to face the sun?’
Caveman ‘You must be stark raving mad! (he stomps the floor vigorously). How can you say the earth is spinning? The earth is rock solid. Standing absolutely still.’
Right there you hit your first major hurdle in this conversation - the one where you need to tell them “Sorry to spoil the party - but the earth is not at the centre of the universe”.
Many of the ancient cavemen (and famous Greek mathematicians) believed that if the earth really spun on its own axis, there ought to be a permanent wind blowing across the earth (the kind of wind that blows across your face if you tried to spin around). Also, they had no instruments to measure wind currents and the likes.
Even when the Greeks invented the sun-dials and measured time by the shadows they cast, the idea that the earth rotates never occurred to them. Here’s how a sun-dial looked (this sun-dial is not from a Greek era, but found in India, to this day).
Since people had believed in this for centuries, it slowly got into the religious texts of the Europeans (namely Christianity). The priests in the churches told all who came to pray that the sun went round and round the earth and that earth was the mighty one holding all planets together. If anyone dared suggest that the sun was actually the one at the center, they would be punished - often times jailed.
Who thought of the sun at the centre?
Very few dared to disagree with the church. Ironically, the man who changed the world’s view was himself a priest at a church. His name was Copernicus. He lived in Poland and preached at a local church. When he had time, he invented a few grand scientific instruments (including better telescopes) and kept noting the position of the stars, the planets, the moon and the sun on an every day basis. He believed that the sun HAD to be at the center of the solar system and everything revolved around the sun. BUT, he was too frightened to say this aloud or publish any written works in his name. He finally gathered a little courage as he grew older and published his very detailed treatise in 1543. His work was called Six Books Concerning the Revolutions of the Heavenly Orbs. He passed away soon after his work was published. Thus he was saved from religious leaders condemning him and his view.
Did things change immediately after Copernicus wrote his work?
Not really (people can be really stubborn)! It took more than 200-300 years for the world to believe that the sun was indeed at the centre of the universe. One of the first to agree with Copernicus was an astronomer called Galileo Galilei. He too invented a fancy telescope with which he noted that the planet Venus changed positions BUT stayed close to the Sun. He deduced that this could be possible only if the earth revolved around the Sun. If the Sun revolved around the earth, Galileo argued that the position of Venus would change as the Sun kept moving around the earth.
Naturally the church got absolutely angry at him and sentenced him to lifelong imprisonment. They were somewhat kind to him and let him stay imprisoned all his life at home (rather than in a jail). Galileo could not interact with the rest of the world (and corrupt other’s minds with the truth about the sun and the earth). Thus the church of Rome felt snug and let this old man conduct his madman scientific experiments, but not share them with the world.
Along came another young man called Kepler. He joined as the assistant to an astronomer, who asked him to observe Mars and plot its orbit. It was Kepler whose careful observations of Mars (and other planets) showed that all of these planets must have an elliptical orbit (not circular, as was assumed by astronomers before him). He drew them all on paper, and showed people how they went around the sun in an ellipse. This began to make a lot of sense to people. Gradually more and more of them began to be convinced that Copernicus must be right and that Ptolemy (and other ancient Greeks) and the Church had to be wrong.
The final straw was when a young man sitting under a tree found an apple falling over his head. He scratched his head as he thought about the apple’s motion and figured that something must be pulling it (yup! we’re talking about dear old Newton). His discovery of gravity helped people understand how the sun’s gravity must be holding all the planets together and make them go round and round the sun!
….and thus we all know that the sun rises in the east and sets in the west - all because the earth spins around itself!