Geocentric Thinkers and Heliocentric Theory in the History of Astronomy (Ptolemy and More Models)

Before civilizations developed enough for people to sit down and really think about tough questions, humans came up with complex mythologies to explain the miraculous world we inhabit. It wasn't until the greatest civilizations developed institutions for knowledge and discovery that people began to mix scientific observation in with their cultural beliefs.

Up until the Enlightenment, Astrology and Astronomy were one and the same. It took a few very dedicated people to lead the way to our modern beliefs about the universe, which tie in so closely to our view of ourselves, religion, and God.

Here are the [abridged] stories of some of these people and their ideas that made our modern world possible.

This theory states that the Earth is the center of everything . It makes sense-- If the Earth moved, wouldn't we would feel that movement?

Claudius Ptolemy, a Roman-Egyptian astronomer from the first century, was a chief proponent of the geocentric model, and believed in something that Plato coined as quintessence. Quintessence, or ether, is basically the heavenly stuff that the cosmos are made of, which was taken very seriously in the science community in the Middle Ages. Nowadays, the poetic word quintessence is used to describe the (hypothetical) "dark" energy that is believed to propel the expansion of the universe.

But back to the point.

Ptolemy saw the universe as a series of domes that surrounded the Earth. Each dome contained a heavenly object-- the moon had a dome, the sun had a dome, and each of the known planets had a dome. Eventually, Ptolemy's theory had 88 domes and explained retrograde. But there was a problem...as science advanced and we humans started discovering more and more things circling around in the sky, this theory got way too complicated, leading to it being discredited.

Heliocentric theory states that the sun is at the center of everything . The radical idea that the Earth revolved around the sun was proposed by a brave astronomer during the 3rd century, but the idea was thrown out by his peers.

The Heliocentric model is truly a development of the renaissance, and was presented by Nicolaus Copernicus, a Polish monk. The funny thing is, this guy didn't even care that much for astronomy- he saw it more as a hobby and focused on math, art, and linguistics. However, he went down in history for sparking the Copernican Revolution, and ideological shift away from Ptolemy's model. His heliocentric theory would later be supported by such great thinkers as Galileo Galilei and Isaac Newton.

This guy was hired to calculate the orbit of Mars based on a circular model of planetary orbit. Kepler worked on this, but had so much trouble fitting Mars' orbit into this model that he abandoned it, and came up with 3 revolutionary laws of planets in movement.

His first law is the Law of Ellipses. This states that planets travel around the sun in ellipses . What the heck is an ellipse? I could give you the physics textbook definition, but I want you to keep reading, so let me try to explain in plain English.

An elipse is a curve that gets interrupted, but still closes up again. Since it's interrupted, it doesn't form a perfect circle when it closes.

Think of that game, tether ball. The ball goes all the way around the pole, but because of its speed and the pull of the rope, it doesn't form a perfect circle. It forms more of an oval. The path of the ball around the pole is an ellipse. This is similar to the path of planets around the sun.

As you see here, the ellipse is a closed curve with two center points. In planetary motion, the sun is one of these points.

This observation was a true breakthrough in understanding how gravity works, and helped to lay the foundation for Isaac Newton's revolutionary theories.

Take a look at the illustration below, which attempts to demonstrate the effects of gravity. Imagine a penny rolling around inside a circular sink. As the penny gets closer to the drain, it speeds up.

Ok look. Take the average distance between the sun and any planet and cube it. The number you come up with is the same as the time it takes that planet to revolve around the sun squared.

Creepy? I guess so.

One side note about Kepler...his mom was put on trial for being a witch, and imprisoned for over a year before the charges were dropped!

The famous and beloved Galileo Galilei was a contemporary of Kepler. It is a common misconception that Galileo invented the telescope, but this is not true. However, he did take the marine telescope, which was commonly used by sailors, and used it to see things in the sky. He discovered that Jupiter had moons revolving around it, which he likened to a mini solar system. This discovery was another blow against Ptolemy's geocentric theory, which was supported by the church at the time.

Galileo also observed sunspots, and was the first person to conclude that the Milky Way was in fact a big collection of stars.

And weird mathematical relationships between planets and orbits and the like aren't the only creepy things going on here! Galileo died in January, 1642. In December of that same year, Isaac Newton was born. Just as spine-tingling as the ideas these guys came up with!

This dashing French fellow on the right actually predicted the existence of Neptune ( ok, so he didn't exactly guess). This was before anyone ever observed Neptune in the sky. He actually calculated this by studying irregularities in Uranus' orbit. He concluded that these interruptions must be the result of another planet whose gravity was pulling on Neptune. If you ask me, this guy has earned a place in history.

I'm leaving out obvious characters, like Isaac Newton and Albert Einstein, who have contributed loads to the science of astronomy. But I'm also leaving out many others who are not so well-known, but whose ideas became the foundations of modern science.

All photos were taken from Wikimedia commons.