Eratosthenes of Cyrene

Hello! My name is Eratosthenes. I was born a very long time ago, around the year 276 BCE, in a sunny Greek city by the sea called Cyrene. Even as a boy, I was curious about everything! I loved reading poetry, studying the stars, and playing with numbers. My friends and teachers gave me a nickname: 'Beta,' which is the second letter of the Greek alphabet. They said I was the second-best at many different subjects. That never bothered me; it just made me want to learn even more about the world!

When I grew up, I traveled to Athens to study with the best minds. Then, around 245 BCE, I received an amazing invitation. The king of Egypt, Ptolemy III Euergetes, asked me to come to the city of Alexandria. He wanted me to be the head librarian at the Great Library of Alexandria! Imagine the biggest library you have ever seen, filled with thousands of scrolls holding all the world's knowledge. It was my job to take care of them and to keep learning. It was the most exciting job in the world for a curious person like me.

One day in the library, I read something fascinating on a scroll. In a city to the south called Syene, there was a deep well. On one special day a year, the summer solstice, the sun's rays shone straight down to the bottom of the well at noon. This meant the sun was directly overhead. But I knew that here in Alexandria, on that same day and time, a tall stick in the ground cast a shadow. How could that be? Suddenly, I had a huge idea! The only way a shadow could appear in one city but not the other was if the surface of the Earth was curved, like a giant ball.

I decided to measure the world! Around 240 BCE, I performed an experiment. On the summer solstice, I measured the angle of the shadow in Alexandria. It was about 7.2 degrees, which is exactly 1/50th of a full circle. Next, I found out the distance between Alexandria and Syene. With those two pieces of information, all I had to do was multiply that distance by 50 to find out how big the whole Earth was! My calculation was incredibly close to what scientists know today. After that, I also created one of the first maps of the known world, invented a clever way to find special numbers called prime numbers, and was the very first person to use the word 'geography' to describe the study of our planet.

I lived a long and wonderful life filled with questions and discoveries, and I lived to be about 82 years old. My work showed that anyone could understand the world using observation, curiosity, and a little bit of math. Today, people remember me as the 'Father of Geography' and as the person who first measured our planet, proving that even the biggest questions can be answered if you are brave enough to ask them.