Changing Ideas about the Solar System

Geocentric model
Image source: http://scienceblogs.com/startswithabang/2010/09/13/geocentrism-was-galileo-wrong/

Geocentric Model
The ancient Greek astronomers believed that the Sun, Moon, planets and stars all orbited planet Earth in perfect circles. This is known as the geocentric model, and was the accepted model of the Universe until the 1500s.

Heliocentric model
Image source: http://scienceblogs.com/startswithabang/2010/09/13/geocentrism-was-galileo-wrong/

Heliocentric Model
Introduced in a book by Copernicus in 1543, however it had been around for around 2000 years. It states that planet Earth and the other planets in our Solar System all orbit the Sun, which is at the centre of the Universe. His book presented astronomical observations that could be explained without having the Earth at the centre of the Universe.

Copernicus' ideas were dismissed by the Church, however one of the most convincing pieces of evidence for the heliocentric model was Galileo's observations of Jupiter's moons. In 1610, Galileo observed Jupiter using a telescope and saw three stars in a line near the planet. The next evening, he noticed that these stars had moved in the wrong direction, and after a week, a fourth star appeared. These four stars never moved away from Jupiter and appeared to be carried along with it – Galileo realised that these objects were not stars, but moons in orbit around Jupiter. This proved that not everything was in orbit around planet Earth, and so the geocentric model was incorrect.

Current Model of the Solar System
The current model states that the planets in the Solar System orbit the Sun, although these orbits are elliptical rather than circular, as suggested by the heliocentric model.