How Earth's size was computed by Eratosthenes
The ancient technique for measuring Earth's radius involved observing the sun's angle at different locations on the summer solstice, allowing Eratosthenes to calculate Earth's circumference using geometry and known distances.
MAIN POINTS FROM TRANSCRIPT
- Eratosthenes used observations from wells in Alexandria and Syene to measure Earth's circumference.
- The summer solstice allowed for predictable sun positioning, crucial for Eratosthenes' calculations.
- The angle difference between Alexandria and Syene was measured as 7 degrees.
- By comparing this angle to a full circle, Eratosthenes deduced Earth's size using known distances.
TAKEAWAYS
- Eratosthenes' method relied on the assumption of parallel sun rays due to its distance from Earth.
- The Tropic of Cancer plays a key role in consistent sun positioning on the solstice.
- Geometry and simple observations enabled ancient calculations of Earth's size.
- Understanding Earth's rotation and axial tilt was crucial for accurate measurements.