Proving the Earth is round. How round you ask? Print this and find out.

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I wanted to create something amazing for my daughter who's due in eight weeks and teach her how we knew our planet was round a long time ago. This model helps people understand this fact and it's also my first time using Tinkercad and M3D Micro printer. I hope you have fun learning about the Earth with this model that shows Eratosthenes' points of measurement. Eratosthenes calculated the Earth's circumference without leaving Egypt. He knew that on the summer solstice in the city of Aswan, the Sun would appear directly overhead at local noon because he had been told that the shadow of someone looking down a deep well would block the reflection of the Sun off the water at the bottom of the well. Using a gnomon, Eratosthenes measured the Sun's angle of elevation in Alexandria and found it to be 1/50th of a circle (7°12') south of the zenith. He may have used a compass to measure the angle of the shadow cast by the Sun. Assuming that the Earth was spherical (360°) and Alexandria was due north of Aswan, Eratosthenes concluded that the meridian arc distance from Alexandria to Aswan must be 1/50th of a circle's circumference or 7°12'/360°. His knowledge of Egypt came from many generations of surveying trips. Pharaonic bookkeepers gave a distance between Aswan and Alexandria of 5,000 stadia, which was checked yearly. Some say that Eratosthenes corroborated this distance by asking people how long it took to travel from Aswan to Alexandria by camel. Carl Sagan says that Eratosthenes paid someone to walk and measure the distance. Some claim that Eratosthenes used the Olympic stade of 176.4 meters, which would imply a circumference of 44,100 km, an error of 10%. Others say he used the Italian stade of 184.8 meters, which implies a circumference of 46,100 km, an error of 15%. It was unlikely that Eratosthenes could have accurately measured the Earth's circumference due to three important assumptions: * Alexandria and Aswan lay on the same meridian * The distance between Alexandria and Aswan was 5,000 stades * The Earth was a perfect sphere Eratosthenes later rounded his result to 700 stadia per degree, which implies a circumference of 252,000 stadia. This might have been done for calculation simplicity as this larger number is evenly divisible by sixty. Repeating Eratosthenes' calculation with more accurate data, the result is 40,074 km, which is 66 km different (0.16%) from the currently accepted polar circumference of the Earth. Seventeen hundred years after Eratosthenes died, Christopher Columbus studied what he had written about the size of the Earth and chose to believe that it was one-third smaller based on a map by Toscanelli. Had Columbus known that Eratosthenes' larger circumference value was more accurate, he would have known that the place where he made landfall was not Asia but rather a New World.