>>11640158Get two long poles, a buddy, a couple tape measures, synchronized clocks, and some cars.
Go to a big ass field (they did this in a desert). Plant one rod in the earth and have your buddy drive longitudinally a good number of miles away and plant their own rod. Record the length of the shadows throughout the day and at what time the shadow is superimposed over the rod (midday). You can use this to calculate the circumference of the earth to a pretty high degree of accuracy if you have a big enough rod and do it right.
Eratosthenes Experiment is the name. google is your friend.
The other method involves a tall sailboat and a spyglass. Watch the sailboat go over the horizon with the spyglass and you will see the bottom disappear before the top. In a flat earth both would slowly disappear at the same time when the limit that light can travel is reached. But on a round earth the bottom will disappear before the top does.
