How Did the Ancient Greeks Use Geometry to Measure the Earth?

The Ancient Greeks used geometry to figure out how big the Earth was, like using a ruler and some clever math to measure something huge.

Imagine you're playing with a round ball on the floor, and you want to know how big it is without touching it. That's kind of what the Greek scholar Eratosthenes did, but instead of a ball, he used the Earth!

Eratosthenes noticed that on a certain day in a city called Syene, the sun shone directly into a well, meaning there was no shadow. But in another city, Alexandria, on the same day, a stick cast a shadow. He used this difference to measure how much of the Earth's surface curved between the two cities.

He measured the angle of the shadow and realized it was about 7 degrees, like a slice of pizza out of a full circle (which has 360 degrees). That meant the distance between the two cities was about 1/50th of the Earth's circumference.

Using that, he did some math and figured out how big the whole Earth was, all from just a shadow, a stick, and geometry! The Ancient Greeks used geometry to figure out how big the Earth was, like using a ruler and some clever math to measure something huge.

Imagine you're playing with a round ball on the floor, and you want to know how big it is without touching it. That's kind of what the Greek scholar Eratosthenes did, but instead of a ball, he used the Earth!

Eratosthenes noticed that on a certain day in a city called Syene, the sun shone directly into a well, meaning there was no shadow. But in another city, Alexandria, on the same day, a stick cast a shadow. He used this difference to measure how much of the Earth's surface curved between the two cities.

He measured the angle of the shadow and realized it was about 7 degrees, like a slice of pizza out of a full circle (which has 360 degrees). That meant the distance between the two cities was about 1/50th of the Earth's circumference.

Using that, he did some math and figured out how big the whole Earth was, all from just a shadow, a stick, and geometry!