At one point we thought that the Earth was stationary and everything in the universe revolved around us. This was called the geocentric model and is shown in the image above. This was all well and good but if you look into the sky from Earth and plot the routes of the planets you will find that they stop and start moving backwards. We know now that this is because we are not a stationary object but in order to make the geocentric model fit epicycles were added.
Each planet was thought to be moving in a circle whilst orbiting the Earth and this is called an epicycle.
As you can see this made the orbits very difficult and some planets had to have different epicycles in order for the model to fit. The calculations meant that Mars took over 7 years to orbit Earth. It was a very hard model for people to let go of because in terms of religion we were thought of as very important people. God created us and so why wouldn’t we be the centre of the universe?
The heliocentric model was introduced by Copernicus and is the model we use to this day. This explained why we saw the planets moving in the way that they do. The epicycles were just an illusion caused by our own orbit around the sun.
Little was known about the universe and this trip back in time makes me grateful to be born into a generation where science is slightly more advanced.