One of the most interesting things I find about the Middle Ages (and through to the early modern period) is its cosmology. Geocentrism was the primary model used during this period, though it was a theory that existed long before the Middle Ages. The Geocentric model is also called the Ptolemaic System, and named for a second century greek astronomer named Claudius Ptolemaeus, who put centuries of Greek thought on this subject together into a working theory.
Ptolemy is most known for his Almagest, which sets out his system of planetary motion and cosmology. The Almagest consists of thirteen books, which deal with everything from former theories from people like Aristotle, to planets and stars and even the moon and eclipses. The main points of his cosmology form the basis for what would be called the geocentric model, and contrary to what our school books told us, the belief in a flat earth was not part of it. The Almagest presents a spherical Earth, at the center of a spherical universe. The Earth itself being a great distance from the stars and merely a point in the universe, but stationary and at its center. This model was taught in the middle ages until Jean Buridan and others would tweak it to suggest a rotating earth which in effect laid the groundwork for a new theory which was heliocentric or Sun centered. Ptolemy’s Almagest found its place among the books of the wise, and is said to be the primary textbook of astronomy used through the middle ages. (paraphrase of C.S. Lewis). It even gets a plug in the Canterbury tales:
“His Almagest, and bookes great and small
His astrolabe, belonging to his art,” from The Millers Tale in Chaucer’s Canterbury Tales
What makes the Geocentric model interesting is the problem of the Sun, which I guess wasn’t a problem for them, but is for me. After all today we know the Earth isn’t the center of the solar system, let alone the universe. So where does the Sun fit in? Well right between Mars and Venus. With the Earth in the center the order of heavenly bodies goes: the Moon, Mercury, Venus, Sun, Mars, Jupiter, Saturn and the Stars. In the pictures you can see the “Via Solis” which is the path or way of the Sun in the fourth ring out from the Earth.
This brings up the next interesting thing for me, that there are only five planets (seven if you count the Moon and Sun). Without a telescope to use, these would be the planets visible to the naked eye. And this point helps explain a lot about the Geocentric model. That it is a model based on observation by the naked eye and from the perspective of the earth. I suppose a lot of fun can be poked at the older cosmology for being wrong, but to see the reasoning, the math, the ground-breaking concepts that developed from such observant people as Ptolemy, Jean Buridan and others; who lacked the benefit of satellites, and telescopes, and computers. This alone makes such leaps in theory, like a rotating earth, simply amazing. Observation would lead anyone to assume it was still. If the Earth did rotate, people argued that a great constant wind from east to west would exist.
One of the problems I have heard made about the Geocentric belief is that it placed the Earth at the center of the universe, being the center of Gods creation. To the Greeks, the center of the universe was not about primacy, and in the Christian mind it wasn’t a place of importance either, rather it was the place of least importance, lowest place. The Earth was surrounded by an invisible fire and above were the heavens. The only thing lower would be the fires of Hell. To look into the heavens, was to look into perfection, a cathedral of life which became more perfect with ascent, until the great you reached the high Heaven. On the maps the last sphere begins the Coelum Empireum Habitaculum Dei et Omneum Electorum which roughly translates as (Heavens kingdom)/(Empyrean Heavens) and dwelling place of God and all the Elect.
Several different models of geocentrism formed through the years trying to piece together new ideas and observations, but it wasn’t until the 16th century that geocentrism began to decline when a theory based on the sun being the center of the cosmos and a man named Copernicus would change everything.