Geocentric model of the universe versus heliocentric model of the universe

The geocentric and heliocentric mdoels of the universe are historical methods of understanding the universe by assuming, respectively, that the Earth is at the centre of the known universe (geocentrism), and that the Sun is at the centre of the universe (heliocentrism), with all other objects orbiting that fixed point.

- Geocentric Model of the Universe -

The geocentric model of the universe, also known as the Ptolemaic model, was widespread beginning in Ancient Greece and holds that the Earth lies at the centre of the universe, with all other objects circling it. This is most intuitively obvious in relation to the Sun and the Moon, which, to an observer on the surface of our planet, do seem to follow regular circular paths over our heads. It is a seemingly empirical conclusion based on the evidence that celestial objects (including stars) circle the sky above us, while the ground beneath our feet appears to be at rest.

Plato and Aristotle both wrote extensively about a geocentric universe, but is best known for another advocate, Claudius Ptolemaeus, of the Roman era. According to Ptolemy, objects orbited the Earth in distinct concentric circles, or spheres. Within these spheres, furthermore, they actually followed elliptical paths within another sphere, called an epicycle. This added complexity was necessary to account for the fact that, viewed from Earth, close objects like the planets Venus and Mars sometimes seem to stop and even to move backwards in the sky.

- Heliocentric Model of the Universe -

Despite the best efforts of geocentric scholars in the medieval and Renaissance worlds to account for these strange perturbations, the geocentric model had serious flaws. These were conclusively exposed beginning in the 1500s by four European astronomers: Johannes Kepler, Tycho Brahe, Nicolaus Copernicus, and Galileo Galilei. These men's systematic observations of the sky indicated that, if indeed objects followed the orbits prescribed by the geocentrists, they could do so only through the arbitrary random intervention of some outside force.

Theoretically there was no reason why God would not choose to move the planets any way he liked, but there was a general assumption that he had probably arranged the universe according to predictable natural laws. Although Copernicus and Galileo were astronomers and not theologians, it is important to recognize that their period was a deeply religious one and therefore that such theological questions did carry some