Ptolemy assumed, like those before him, that the Earth was at the center of the Universe, and that it was stationary. In his model, everything else moved around it and had circular orbits.
The geocentric model had trouble explaining one observed aspect of planetary motion called retrograde motion, where some planets move across the sky relative to the background stars, then slow down, appear to move "backwards," and move normally again. (Here is a simulation)
We now know that this is due to the fact that the Earth catches up and passes these planets in their orbits, so the planets appear to move backwards for a little while (Fig. 1.12 in book). The outer planets move more slowly in their orbits than the inner planets do, so they pass the outer planets regularly.
Ptolemy (Greek; 140 A.D.) developed a complicated geocentric model where the planets moved on little circles (called epicycles) while orbiting the Earth (Fig. 1.13 in book). It was an incredibly ingenious model for his time, but it was wrong.
The heliocentric model was first put forth by Copernicus in 1543 (1400 years after Ptolemy!!)
Copernicus believed that the Earth was a planet, and it and all other planets orbit the Sun, with only the Moon orbiting the Earth.
Pros:
Cons:
As a result of these difficulties, the heliocentric model was not accepted when it was first proposed. Nearly a century had to elapse before the heliocentric model got a boost...
Galileo (Italian) was the first person to use the telescope for astronomical viewing (1610)
He made several important observations that supported the heliocentric model:
Consequences of Galileo's adoption of heliocentric model: house arrest in 1616 until his death; church admitted they were wrong in 1992
