- Ancient Greek science
- Greek innovations
- Spread of knowledge
- Ptolemy model


[SLIDE 1]

Modern science traces its roots back to ancient Greece. Greece rose to power in the Middle East around 800 B.C. and was well established by 500 B.C.

Greece was a crossroads for travelers, merchants and armies from northern Africa, Asia and Europe, so Greek philosophers were able to build on a diverse array of ideas from many different cultures.


[SLIDE 2]

The Greeks were responsible for three innovations in philosophy that had repercussions in science and all of human society.

First, they sought to understand nature without supernatural explanations and by debating ideas.

Second, they used mathematics for precision.

Finally, they used the power of reasoning from observations. They acknowledged that reasoning could not be right if physical evidence or facts contradicted them.


[SLIDE 3]

Using these innovations, the Greeks developed models for explaining and predicting observed phenomena. They made conceptual models of the universe. By 500 B.C, the mathematician Pythagoras taught the idea that the Earth was round. This concept was widely accepted by then and had replaced ancient beliefs that the earth was flat.

Aristotle looked at Earth's curved shadow on the Moon during lunar eclipses to prove that the Earth was spherical. The Greeks believed that the Earth is part of a system of planets and stars. The Greeks also adopted a geocentric model of the universe with the Earth at the center of the universe. 


[SLIDE 4]

Greek philosophy and ideas spread rapidly through Europe beginning with Alexander the Great's conquests of Europe from 356 to 323 B.C. While there are not a lot of books from this period, some Muslim scholars in Baghdad saved Greek works and translated them into Arabic. These Muslim scholars also pulled ideas from Hindu scholars from India and ideas from China. They were able to combine all this knowledge and ultimately developed the first tools of mathematics for algebra and astronomical observation.

This sharing of knowledge ignited the European Renaissance.


[SLIDE 5]

The Greek model of the Earth as the center of the Universe, the geocentric model, turned out to be inaccurate but it did offer the first way to see the Earth as part of a larger system of stars and planets. There were many versions of the geocentric model developed by the Greeks, but the final model was developed by Claudius Ptolemy. 

In the Ptolemy Model, each planet moved on a small circle, called an epicycle, whose center moved around the Earth in a larger circle, called a deferent. This model was clever because it kept with the ancient belief that the heavenly bodies had to move in perfect circles while at the same time managing to explain the phenomenon of apparent retrograde motion.

In spite of its faulty Earth-centered premise, the Ptolemy model did correctly forecast future planetary positions within a few degrees of arc and was in use for the next 1500 years.

Ptolemy's work also helped in building the perspective of a rotating Earth with each planet in the star system independently moving in a circular motion.