🌍 Who Calculated the Earth’s Circumference — and How?

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🧠 Who did it?

The first person to calculate the Earth’s circumference was Eratosthenes
👨‍🏫 He was a Greek scientist who lived more than 2,200 years ago (around 240 BCE).

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📏 What is Earth’s circumference?

• The circumference is the distance all the way around the Earth.
• Today we know it is about 40,075 km around the equator.

What’s amazing is that Eratosthenes got very close to this number without satellites or modern tools!

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☀️ How did Eratosthenes calculate it?

He used:

• 🌞 The Sun
• 📏 Shadows
• 🧠 Smart thinking

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🪜 Step-by-step (simple explanation)

1️⃣ A strange observation

Eratosthenes knew that:

• In a city called Syene (now Aswan, Egypt),
  • At noon on a certain day, the Sun was directly overhead
  • No shadow was seen at the bottom of a deep well

But in another city…

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2️⃣ A shadow appears

• In Alexandria, at the same time, a stick did cast a shadow
• He measured the shadow and found the angle was about 7.2°

🧠 This angle is 1/50 of a full circle (360°)

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3️⃣ Measuring the distance

• He knew the distance between Syene and Alexandria
• It was about 800 km

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4️⃣ The big calculation

If 7.2° = 800 km,
then 360° = 800 × 50 = 40,000 km

🎉 That was his answer!

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🤯 Why is this so amazing?

• He didn’t:
  • Travel around the Earth
  • Use satellites 🛰️
  • Use airplanes ✈️
• He only used:
  • A stick
  • Shadows
  • Math
  • His brain 🧠✨

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🧠 Easy to remember

Eratosthenes measured Earth using sunlight and shadows ☀️📏

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⭐ Fun facts for kids

• He lived over 2,000 years ago
• His answer was very close to today’s measurements
• This proved the Earth is round
• He also worked at the Library of Alexandria, one of the greatest libraries ever

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