Tag

mathematics

• Eratosthenes measures the EarthAbout 240 BC, one angle (7.2°) and one distance gave the size of the whole planet.
• The shadow stick and why the lines meet at Earth's centerHow the 7.2° was measured at Alexandria, and why a plumb line points to the center of the Earth.
• Why the sun's rays count as parallel (Aristarchus)The Greeks already knew the sun was very far away, so rays reaching two cities 500 miles apart are effectively parallel.