Found it. My post for last week's class

9/12/12

We learned about the science of Astronomy last week. We learned how astronomical observations helped ancient societies. They were benefited because it helped keep track of time and the seasons. These observations also helped them with navigation. There were many different achievements as well. Ancient astronomers were able to tell the time of day and the time of year, and were able to observe planets and stars.

We also learned about how modern science traces it's roots to the Greeks and how the Greeks explained planetary motion. The Greeks had the Ptolemaic model, which explained apparent retrograde motion by having each planet move on a small circle whose center moves around the Earth on a large circle.

We learned about Copernicus, Tycho, and Kepler. Copernicus created a Sun-centered model of the solar system, but was still not correct as it used perfect circles. Tycho provided data to improve his model, and Kepler developed a model of planetary motion that fit Tycho's data. We learned about Kepler's 3 laws:

1.) The orbit of each planet is an ellipse with the Sun at one focus.
2.) As a planet moves around its orbit, it sweeps out equal area in equal times.
3.) More distant planets orbit the Sun at slower average speeds, obeying the precise mathematical relationship p squared equals a cubed.

Galileo's telescopic observations was able to help overcome objections to the idea of Earth orbiting the Sun.