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

I wanted to make something that I could show my daughter (due in 8 weeks) how we learned long ago that our planet was round. This is a small model to help conceptualize this fact. I've placed the sticks in the approximate locations of Eratosthenes' points of measurement. This was also my first time using Tinkercad and my M3D Micro printer. I hope you have fun using this little thing to help prove our planet is round!

Eratosthenes calculated the circumference of the Earth without leaving Egypt. Eratosthenes knew that at local noon on the summer solstice in the Ancient Egyptian city of Swenet (known in ancient Greek as Syene, and now as Aswan) on the Tropic of Cancer, the Sun would appear at the zenith, directly overhead. He knew this because he had been told that the shadow of someone looking down a deep well in Syene would block the reflection of the Sun at noon off the water at the bottom of the well. Using a gnomon, he measured the Sun's angle of elevation at noon on the solstice 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 that Alexandria was due north of Syene, he concluded that the meridian arc distance from Alexandria to Syene must therefore be 1/50th of a circle's circumference, or 7°12'/360°.

His knowledge of the size of Egypt was founded on the work of many generations of surveying trips. Pharaonic bookkeepers gave a distance between Swenet and Alexandria of 5,000 stadia (a figure that was checked yearly). Some say this distance was corroborated by inquiring about the time that it took to travel from Syene to Alexandria by camel. Carl Sagan says that Eratosthenes paid a man to walk and measure the distance. Some claim Eratosthenes used the Olympic stade of 176.4 meters, which would imply a circumference of 44,100 km, an error of 10%, but the 184.8 meter Italian stade became (300 years later) the most commonly accepted value for the length of the stade, which implies a circumference of 46,100 km, an error of 15%. It was unlikely, even accounting for his extremely primitive measuring tools, that Eratosthenes could have calculated an accurate measurement for the circumference of the Earth due to three important assumptions he made (none of which are perfectly accurate):

That Alexandria and Syene lay on the same meridian,
That the distance between Alexandria and Syene was 5000 stades,
That the Earth was a perfect sphere.
Eratosthenes later rounded the result to a final value of 700 stadia per degree, which implies a circumference of 252,000 stadia, likely for reasons of calculation simplicity as this larger number is evenly divisible by sixty.[17] 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' death, while Christopher Columbus studied what Eratosthenes had written about the size of the Earth, he chose to believe, based on a map by Toscanelli, that the Earth's circumference was one-third smaller. Had Columbus set sail knowing 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.
Source: Wikipedia- https://en.wikipedia.org/wiki/Eratosthenes#Measurement_of_the_Earth.27s_circumference