The story of the Solar System – how have our ideas changed

Egyptian & Chinese Astronomy - Used star maps to place festivals - Work out when to sow and harvest the crops Babylonian astronomy - considered the celestial bodies to be Gods Greek Astronomy – used starts for navigation Ancient Times

Thales (Thay-lees), ( BC.) He thought the Earth floated in water, was stationary and at the centre of the universe; closest to Earth is the Moon. His explanation was based on observed motion of the planets orbiting the Earth. Geocentrism

Pythagoras, ( B.C.) Pythagoras and his followers were the first to consider the Earth as a globe revolving with the other planets around a central fire (the Sun but was unknown at that time). However this was not taken seriously. Heliocentrism

Aristotle, ( B.C.) Was the first person to state that the Earth was spherical, although his theory was not taken seriously at the time and was based more on philosophy than on actual evidence. He also believed that the Earth was at the centre of the universe and that everything including the Sun orbited the Earth. Geocentrism

Aristarchus of Sámos, ( B.C.) First person known to have proposed our modern view of the universe: The Earth was at the centre of the Solar System and Earth turned on its own axis every 24 hours. His work was firmly grounded in observation and mathematics. He went on to calculate the approximate distance from the Earth to the Sun. Unfortunately most people did not take his work seriously. Heliocentrism

Ptolemy, (200 A.D.) 1) Supported Aristotle’s findings. 2) Drew a map showing the Universe with the Earth at the centre and the Moon and Sun orbiting it. This model was known as the geocentric model (“geo” means Earth). This was accepted for over a thousand years. Geocentrism

Geocentrism (Geo = Earth, kentron = Centre)

Copernicus, ( A.D.) Copernicus said the Sun was at the centre of the Universe, with the planets going around it. His model was called the heliocentric model (“helio” means Sun). Copernicus knew that the church authorities would be strongly against his ideas, and did not publish them during his lifetime. Heliocentrism

Heliocentrism (Helios = Sun and kentron = Centre )

Kepler, ( A.D.) Used many of people’s observations and measurements to devise laws of motion for the planets. He showed that they moved not in circles but in elliptical (oval) orbits. Heliocentrism

A model of Kepler’s elliptical orbits:

Galileo, (1564 – 1642 A.D.) With the aid of telescope of his design was the first to report astronomical observations. His observations confirmed that Copernicus was right and that Ptolemy’s model of the planetary motions was wrong. He detected four moons orbiting Jupiter, which showed that not everything orbits Earth. One argument against the idea that Earth orbits the Sun was that the Moon would be left behind. Galileo’s observations clearly disproved that argument. After all, Jupiter’s moons were able to keep up with Jupiter. His attempts to publicise the Copernican system caused him to be tried by the Church for heresy and he was condemned to house arrest in Heliocentrism

Sir Isaac Newton ( A.D.) Newton explained about the elliptical orbits based on Kepler’s work. The planets are held in elliptical orbits by the gravitational attraction of the Sun. Heliocentrism