changing ideas about the solar system
Most ancient Greek astronomers thought the sun, moon, planets and stars all obited the Earth in circles. This is called the geocentric model
The heliocentric model says the sun is at the centre of the universe.
It also says the Earth and planets all orbited the Sun.
In 1543, copernicus showed space observations could be explained without having the Earth at the centre of the universe.
At first, many people didn't believe in the heliocentric model.
Galileo's observations of Jupiter helped change that.
In 1610, Galileo was looking at Jupiter using a new invention - the telescope.
He saw four/4 stars which never moved away from Jupiter.
He realised they weren't stars, but were moons orbiting Jupiter.