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Until the early 1500s, everyone thought that the planets, Sun and stars all went round the Earth. We now know that this is not true and that the Earth and the other planets go round the Sun, which is just one of many stars in our galaxy. The first person to say this was an astronomer called Copernicus, but he wrongly thought that the Sun was still the centre of the Universe. His ideas were not really believed until after the work of Kepler and Galileo.
Johannes Kepler spent a lot of time looking at the movement of Mars. From this he found that all of the planets move in ovals around the Sun.
Galileo built his own telescopes after they were invented in 1609. He used them to look at our Moon, the planets, the moons of Jupiter and other stars in our galaxy. He agreed with Copernicus’ ideas and supported them in his book. After it was printed in 1632, he was arrested, and was not allowed to leave his house for the rest of his life, because the Catholic Church didn’t agree with him.
In 1687 the English physicist Isaac Newton came up with his Law of Gravitation. This says that all objects in the Universe are pulled towards each other. Even you and the computer you are using are pulling on each other, but you don’t notice it because you are both very light, and so the pull is not very strong. It is only with very heavy objects, such as planets and stars, that we notice the pull. We feel this every day because the Earth pulls on us and keeps us on the surface instead of floating off into space. This is what we call gravity.
Click on the links below to find out more about the Universe.
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Authors: Carolyn Brinkworth and Claire Thomas
Last updated: July 2001