Solar System

• The Solar System consists of the Sun and the nine Planets in its orbit. This includes Moons, the Asteroid belt, meteors and comets.
• The Nine Planets are Mercury, Venus, Earth, Mars, Jupiter Saturn, Uranus and Neptune.

The Seven Planets of the Classical World

• The Seven Classical Planets are described in detail in Ptolemy's Almagest and were the seven visible moving stars whilst all the other stars were fixed.
• The Greek word for planet means ‘wanderer’, and these were the seven stars that moved across the sky in contrast to the fixed stars.

1. • Moon
   • Sun
   • Mercury
   • Venus
   • Mars
   • Jupiter
   • Saturn

A Heliocentric or Geocentric Universe?

Aristotle (c.384-322 BCE)

• Aristotle taught a Geocentric universe where all the planets including the Sun orbited the Earth.

Hipparchus (c.190-c.120 BCE)

• Hipparchus produced a Star Catalogue, and proposed a Heliocentric Universe with the Sun at the centre.

Ptolemy’s Almagest (c.150 CE)

• Ptolemy (c.90-168 CE) published a star catalogue, and based his system on a geocentric universe with the Earth at the centre.

Copernicus (1543 CE)

• The geocentric Universe continued to be accepted until it was challenged by Copernicus in 1453, then by Kepler, Brahe and Isaac Newton. Within 100 years it was accepted that the Universe was Heliocentric.