1. A Short History of Astronomy Ancient (before 500 BC) Egyptians, Babylonians, Mayans, Incas, Chinese Classical Antiquity (500 BC-500 AD) Greeks, Romans: Plato, Aristotle, Ptolemy Middle Ages (500-1450 AD) Arabic astronomers Renaissance (1450-1550 AD) Copernicus Baroque (1550-1700 AD) Brahe, Kepler, Galilei, Newton

2. Ancient Astronomy Stonehenge, England Pyramids, Gizeh near Cairo, Egypt

4. “Strange” motion of the Planets Planets usually move from W to E relative to the stars, but sometimes strangely turn around in a loop, the so called retrograde motion. (Explanation: next lecture!)

5. Retrograde Motion

6. Ptolemy (~140 AD) Puts forth a complete geocentric model dominates scientific thought during the Middle Ages Longest lasting (wrong) theory ever: 1000yrs Major Work: Almagest

7. Epicycles Ptolemy’s explanation of retrograde motion About 40(!) epicycles necessary to explain all observations  complicated theory

8. Nicolas Copernicus (1473–1543) Rediscovers the heliocentric model of Aristarchus  BOOKS! Planets on circles  needs 48(!!) epicycles to explain different speeds of planets Not more accurate than Ptolemy Major Work : De Revolutionibus Orbium Celestium (published posthumously)