Ancient Greek Astronomy: Lesson for Kids

Instructor: David Wilson

David has taught college history and holds an MA in history.

Despite living thousands of years ago, the ancient Greeks developed a remarkable understanding of the world and its place in the galaxy by studying astronomy. Learn about their achievements in this lesson.

Finding Your Way

If your best friend challenged you to a race around the world, would you accept? Don't answer too quickly, because you don't get to use Google Maps to find your way around. In fact, you don't even get a map: you have to figure out how to get from point A to point B the way that people did centuries ago, with the sun and stars.

It sounds difficult, but thousands of years before the internet, people began studying the sky to figure out their place in the world. The ancient Greeks were able to advance our understanding of astronomy without ever using a telescope.

Ancient Greek diagram of the size of the Sun, Moon, and Earth
Ancient Greek astronomy calculations

Looking Up

About 2,500 years ago, the Greeks realized that the Earth is a sphere, meaning that it's shaped like a round ball rather than just a flat surface. We don't know much about what they knew or believed prior to this since it took place so long ago. However, the oldest ancient Greek astronomers realized that during a lunar eclipse (when the Earth is between the Sun and the Moon), the shadow on the moon is round, which means that Earth is round.

Lunar eclipses gave ancient astronomers more opportunities to understand the world and the solar system than just realizing the Earth is round. They also helped them understand the size of the Earth. An astronomer named Eratosthenes measured the shadows cast by the Sun in order to understand the size of the Earth and, using only these measurements and some math, managed to measure the size of the Earth. Thousands of years later, we can calculate the exact size, and it turns out Eratosthenes wasn't far off.

Aristotle and Astronomy

One of the most famous ancient Greek astronomers is Aristotle; he's also considered one of the most important scientists of the ancient world. The ancient Greeks thought about the stars and heavens differently than we do today: they believed them to be unchanging and perfect. Aristotle believed that the Earth was geocentric, or the center of the solar system. Another astronomer named Aristarchus claimed the Sun was the center, but he wasn't as popular as Aristotle. It would take over 1,500 years after Aristotle until scientists realized the Earth went around the sun, not the other way around.

Statue of Aristarchus, Greek astronomer

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