Western History 97: What was the Heliocentric Revolution?

The Heliocentric Revolution is arguably one of the greatest developments in the history of science. It involved the systematic overthrow of the older Geocentric model (that placed Earth at the center of the Universe) with a newer model that gave universal primacy to our sun ie. Heliocentric Model. From a philosophical basis this would also change the way thinkers in the West would have to reframe our importance in the universe. Politically it would weaken the power of established religion (who largely backed the Geocentric model) by calling into question their supposed infallibility in the Sciences

Key dates in the History of this Revolution are outlined below

4^th century BC – Plato, Eudoxus and later Aristotle develop progressively more sophisticated geocentric models on the notion of spheres carrying the planets and the sun around the Earth.

3^rd Century BC – Aristarchus of Samos proposes an early Heliocentric model.

2^nd Century AD – The Alexandrian Greek Astronomer draws heavily from both Hellenic and Babylonian work to produce his work the Almagest. According to Ptolemy each planet moves on two spheres – a deferent and an epicycle. The deferent has its center at the location of the Earth. The epicycle is a separate sphere that allows for motion independent of the deferent.  He includes the stars in his model and makes space for the Prime Mover. Retrograde motion (apparent backward motion of planets like Mars) are explained using epicycles. Ptolemaic Model remains dogma in both the West and the Middle East for well over a millennium.

1543 – Nicolas Copernicus publishes (on his death bed) his famed De revolutionibus orbium coelestium, "On the revolutions of the heavenly bodies. Copernicus, a Polish Monk was trying to correct the seasonal inaccuracies associated with the Ptolemaic model. He places the Sun at the center of the Universes and argues that all the planets including the Earth orbit the sun in circular patterns. Book would be denounced by both Martin Luther and ignored by the Catholic Church until 1616.

1587 – Danish astronomer Tycho Brahe collects a great deal of data about the Motion of Mars. He also develops a third model that has all the planets orbiting the sun but then the sun orbiting around the Earth.

1609- 1619 – Johannes Kepler using Brahe’s data develops this Three Planetary Laws. Kepler provides a mathematical platform for the elliptical orbits of all planets around the sun, describes the relationship between their speeds and the areas they sweep out and relates the period of orbit to the distance. These laws still hold today.

1610 – With the development of the telescope – Galileo Galilei shows that it is possible for bodies to orbit other planets (he observed the moons of Jupiter). He also studied the phases of Venus that could only be explained by heliocentric motion. However his strong advocacy on behalf of the Heliocentric model (as evidenced in his Dialogue Concerning the Two Chief World Systems) resulted in him falling foul of the Church Inquisition and his subsequent house arrest for heresy.

1687 – Sir Isaac Newton publishes the Principia where he shows how Galileo’s concept of inertia plus his Law of Universal Gravitation are the only ingredients needed to explain how the planets (including Earth) orbit the sun (Newtonian Synthesis). Final victory for the Heliocentric Model.