Greek Astronomy
Greeks knew earth was spherical
- Eratosthenes measured earth circumference 200 BC f.4-9
- Sun reaches zenith in Syene at noon, summer solstice
- well points toward zenith
- Syene latitude = 23.5 deg N
- right on Tropic of Cancer
- Shadows at Alexandria indicate sun 7 deg. from zenith
- Small Angle Formula, naturally!
- What is latitude of Alexandria?
- circumference = (360o/7o) x (distance Syene-Alexandria)
- Aristotle argued the earth was spherical
- Earth’s shadow circular during lunar eclipse
Plato and Aristotle misunderstood motion
- Thought continued motion required a motive force
- familiar with every day experience