What do you see in the night sky as time goes by? Do all objecets stay still? Do they appear to move? If so, how?
In ancient times, it was believed that the Earth was the center of the known Universe. [At that time, the Universe consisted of the Sun, Moon, Earth, Mercury, Venus, Mars, Jupiter, and Saturn, along with the stars in the night sky.] This idea was put forth by Ptolemy, a Greek philosopher, and was held as the dominant view of the universe for nearly fifteen hundred years. Most of early astronomy was based on predicting the positions of planets in the night sky.
Earth at center, assumed to be stationary, everything else moved around it and had circular orbits
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 (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)
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). It was an incredibly ingenious model for his time, but it was wrong.
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:
first to use the telescope for astronomical viewing (1610)
made 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