We discussed the development of Astronomy, which stretches well back into prehistory. Among the most obvious early cycles are the day/night and monthly lunar phase cycles. It was clear that the planets move among the stars in a narrow band in the sky (the Zodiac). The rise of agriculture led to the need for a calendar. All cultures have cosmologies, which discuss the origin and overall nature of the Universe. These vary wildly in their details. Over 2000 years ago, the Greeks had deduced the size and shape of the Earth, and used mathematics and geometry to deduce and predict astronomical events. Ptolemy used the circle and uniform motion to develop an Earth-centered (geocentric) cosmology and explain the motions of the planets. Arguments that the Earth stands still included "common sense", the lack of stellar parallax, success of the model in predicting planetary positions, and general self-importance. Arguments for a Sun-centered (heliocentric) model included the importance of the Sun for life and the fact that it seemed to be bigger than the Earth (by lunar geometry).

The Ptolemeic model held sway in the West until after Copernicus, who preferred a heliocentric model on mostly asthetic grounds (because of uniform circular motion in his model too, it didn't predict planetary positions any better). It wasn't until Galileo used a telescope on the heavens that there was real observational evidence to overturn the old model. This included the imperfection of cosmic bodies (craters on Moon, spots on Sun), phases of Venus, and the moons of Jupiter (the latter 2 of which were clear evidence that not everything went around the Earth). Galileo was an early practitioner of the scientific method, using experiment to verify and form hypotheses, and careful observation to deduce underlying physical laws.

The class notes on History of Astronomy.