Tuesday, March 15, 2011

The Geocentric Universe - Part 3

Late Greek Cosmology

I have deliberately omitted Aristotle and Plato up to this point.  The series of posts presented here are for the most part in chronological order. The reason for the omission is that of the philosophers and great thinkers of the Greek time, many had tried to separate heavenly influence from the science but this did not continue in most part due to Aristotle (384 – 322 B.C). At the time Aristotle was considered by many as the greatest thinker of his age much the same as we now see Newton or Einstein. With a person held in such reverence very few would dare put forward theories that would challenge or contradict Aristotle.

Raphael's School of Athens.
Note the two central figures of Plato and Aristotle
Aristotle believed in a hierarchical view of the cosmos. To him there was a major distinction between what he saw as an imperfect world of change and the eternal and immutable heavens. To him the heavens were perfect such that all bodies revolved about the Earth in perfect circles. Due to his influence this view was held in the highest regard and most other theories fell by the way side. Many had argued for the divorce of mysticism from science but the view put forward by Aristotle again united them.

This view was upheld by Plato (424 – 448 B.C) who dismissed natural science in favour of believing in the perfect heavens with the imperfect and changing Earth at the centre. Plato at this time established his academy (which would continue to teach for almost 900 years); through this academy these teachings would gain prominence and would dominate cosmology for centuries to come.

People now would question why did this view point persist even when faced with some major errors? This model could not explain why the planets moved with retrograde motion or following on from that when the brightness of the planets varied. To us now it almost seems foolish but it has to be remembered that this was Aristotle and other renowned philosophers’ viewpoint and as such it was accepted. Also as stated earlier humans like to see themselves at the centre and it fitted the views of many people and their religion.

The geocentric model championed by Aristotle persisted even with its flaws. With the quality of the measurements that could be made of the night sky at the time of the Greeks it was obvious that it was incorrect, this however was about to change. The rise to fame of Ptolemy (83 – 161 AD) would cement the geocentric model in cosmology. Many had tried to come up with explanations to support the geocentric model of perfect circular orbits but none could find a satisfactory answer. Ptolemy however tackled and solved this problem with the use of complex geometric patterns.

In Ptolemy’s theory (published in his treatise Almagest) the Earth remains stationary at the centre which each planet orbiting in a perfect circle known as a deferent. Within this deferent the planet moved with a circular motion known as an epicycle. Each planet had multiple epicycles. To add to this complexity planets also orbited in what was known as an equat. The equat was an offset for each orbit which placed the Earth not at the centre but slightly off. This eccentric model solves some the problems with the orbits. This model was highly complex but it did allow for good navigation and was able to provide somewhat accurate celestial predictions. With the apparent victory for this model and with the president set by Aristotle and Plato before, the geocentric model would prevail for centuries to come.

Ptolemy's Geocentric Model
The Dark Ages

The term Dark Ages refers to a time in Europe which spans from the late 5th century to the start of the 11th century. This is a list of discoveries in chronological order note the lack of advancement between the 5th and 11th centuries within Europe. This era was started with the fall of the Roman Empire and the collapse of the Greek states. Many of the great works of the Greek philosophers had been lost. With the religious turmoil and denigration this all added to the problems of the everyday person at this time. With such upheaval, stable government, schools and many forms of academia were now a distance memory. The only stabilizing force within this time was organised religion. The Catholic Church at this time was a powerful force and with such troubling times in Europe many turned to god for comfort.


While Europe seemed to have fallen from grace, the Muslim and Islamic civilizations flourished. They embraced many of the mathematical ideas from the Greeks along with their astronomical observations. Science developed within these cultures greatly during this time period. Trade with the east from India introduced many other concepts which they embraced. This upsurge in science would bring Europe out of the “darkness” it had endured for centuries. The Spanish had retaken many of the towns and cities conquered by the Muslims in which they found vast libraries of scientific teachings dating back to the time of the Greeks. These discoveries would help lay the foundations of learning within Europe and herald a new beginning in science.

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