The Heliocentric Theory of the Solar System

The Geocentric Theory

• The geocentric theory asserts that Earth is at the center of the Universe and that all objects in the night sky orbit around it. This theory, long since disproven, gained popularity in ancient China and Greece and was supported by such influential thinkers as Aristotle and Ptolemy. Evidence supposedly came from the fact that the Sun, stars, and planets appear to revolve daily around the Earth and that the Earth is sold and stable. Since the Earth appears to be unmoving, thinkers reasoned that other bodies must orbit it.

First Proponents of the Heliocentric Theory

• Aristarchus, a Greek philosopher and mathematician from the isle of Samos, was the first proponent of the heliocentric theory in ancient Greece. He lived from approximately 310 to 230 BC. His only surviving work, "On the Sizes and Distances of the Sun and Moon," makes no reference to his heliocentric theory. In this treaty, he calculated that the Sun was seven times the diameter of the Earth and 300 times its volume. His calculations were far from the actual ratios; the Sun is actually 300 times diameter of the Earth and 1,300,000 its volume. However, the realization that the Sun is much bigger than the Earth probably led him to the conclusion that the Earth actually orbited the Sun. While no copies of the book he wrote about the heliocentric solar system remain, there are references to it, particularly in the work of Archimedes.

Copernicus

• While the heliocentric theory fell out of favor, it was later revived in the 16th century by Nicolaus Copernicus. He based his own formulations on Aristarchus's work, and he published his findings in "On the Revolutions of the Heavenly Bodies." In his model, he used geometry to correctly identify the Earth as the third planet from the Sun and asserted that the moon orbits the Earth rather than the Sun. He also theorized that the stars do not orbit the Earth, but rather, the Earth itself rotates which makes it seem as if the stars transit across the sky. The Italian astronomer Galileo Galilei built a telescope and helped provide observational proof for the theory, although he erred in assuming that the planets followed circular orbits. Johannes Kepler later proved that the orbits of the planets are elliptical.

Church Opposition

• One of the main factors hindering the development and dissemination of the heliocentric theory was first the opposition of such influential philosophers of Plato and Aristotle, and then the implacable opposition of Roman Catholic Church. It considered the heliocentric theory heretical and may have influenced Copernicus to withhold publication of his theory until he was on his deathbed. Following Copernicus's death, the Church put Galileo under house arrest for promoting the heliocentric theory.