Geocentric and heliocentric Theories

Our understanding of the solar system has changed over many centuries. Scientists such as Ptolemy, Copernicus and Galileo added their ideas to our changing understanding. We observe the universe using a variety of equipment, from telescopes to orbiters and landers.

The planets and the Sun orbit the Earth in Ptolemy's model.

Our understanding of the universe has changed over time. Different civilisations have created different models to explain what the universe is and how the universe began. The Greek astronomer Ptolemy (c90-168AD) used measurements of the sky to create his geocentric model. This had the earth at the centre and all the planets and the sun orbiting around it.

The geocentric model lasted a long time. It wasn’t until the mid 18th century that Nicolaus Copernicus (1473-1543) came up with a different model. His heliocentric theory put the sun at the centre if the universe. It was based on observations with the telescope – work pioneered by the Italian astronomer Galileo Galilei (1564-1642).

Discovering new planets

As telescopes have improved scientists have discovered new planets. Copernicus’ model of the universe didn’t include Uranus, Neptune or the dwarf planet Pluto because telescopes at the time weren’t good enough to see them.