3. Earth

5. Aristotle BC 384-322

6. Aristotle

7. Geocentric model

8. Nicolas Copernicus 1473-1543

9. Eyeball observations De Revolutionibus The Earth rotates on its axis once daily and revolves around the Sun once yearly.

10. Heliocentric Model

12. Tycho Brahe (1546-1601)

13. Johann Kepler (1571-1630)

14. Kepler’s 1 st Law “ellipses”

15. Kepler’s 2 nd Law “equal areas in equal times”

16. PlanetPeriodDistanceP/DP/D 2 P 2 /D 3 Mercury0.240.390.621.600.99 Venus0.620.720.851.181.00 Earth1.00 Mars1.881.521.230.811.00 Jupiter11.95.202.280.441.00 Saturn29.59.513.100.331.01

17. Kepler’s 3 rd Law “Harmonic Law”

18. Astronomical Unit Average Distance to Sun from the Earth 1 A.U. = 150 million km Examples: Mercury 0.4 A.U. Neptune 30 A.U.