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Summary

The video discusses Eratosthenes' remarkable experiment from around 190 BCE, where he determined that Earth is round and calculated its circumference with impressive accuracy. Using basic tools like shadows and measurements from two cities, Syene and Alexandria, Eratosthenes observed that sunlight hit them at different angles. From this, he concluded Earth was curved and calculated its circumference to be approximately 40,000 km, close to modern-day measurements. The video demonstrates this experiment with simple objects, emphasizing the significance of Eratosthenes' discovery in ancient times.

Takeaways

• 🌍 Eratosthenes, an ancient scientist from 190 BC, made a significant discovery about the shape of the Earth, proving that it is spherical, not flat.
• 🧪 Through a series of experiments, Eratosthenes calculated the Earth's circumference with remarkable accuracy using simple observational methods.
• 🛠 He used a lamp to represent the sun and two objects at different latitudes to demonstrate the Earth's curvature.
• 🗺 Eratosthenes compared two cities, one at the equator and another at 23° latitude, to observe the difference in shadow lengths, proving that the Earth is curved.
• 📅 He noted that in Pontianak, during the equinox, there is no shadow at midday, but at other latitudes, shadows appear, showing Earth's roundness.
• ⚖️ By observing the difference in shadows between Alexandria and Syene, Eratosthenes calculated that the angle of the shadow in Alexandria was 7.2°, which he used to estimate the Earth's curvature.
• 🧮 Using simple geometry, he compared the 7.2° angle to the full 360° circle and the distance between the two cities (5,000 stadia) to compute the Earth's circumference.
• 📏 He calculated that the Earth's circumference was 250,000 stadia, which converts to approximately 40,125 km, very close to modern measurements.
• 🔍 The accuracy of Eratosthenes' method is remarkable considering the limited tools and knowledge available at the time.
• 👏 Eratosthenes' discovery laid the foundation for understanding the Earth's spherical shape and its size, and his work remains relevant even in modern science.

Q & A

Who was Eratosthenes and what significant discovery did he make about the Earth?

Eratosthenes was an ancient Greek scientist who lived around 190 BC. He made a significant discovery that the Earth is not flat but spherical, and he also calculated its circumference through a series of experiments.

How did Eratosthenes prove that the Earth is spherical?

Eratosthenes used observations of shadows in two different cities, Syene (modern-day Aswan) and Alexandria, during the summer solstice. He found that in Syene, the Sun was directly overhead with no shadow, but in Alexandria, there was a shadow, indicating that the Earth is curved.

What assumption did Eratosthenes make about the Sun’s rays for his experiment?

Eratosthenes assumed that the Sun’s rays are parallel when they reach Earth because the Sun is far enough from the Earth that the rays arrive in straight lines.

What two cities did Eratosthenes use for his experiment, and what was the distance between them?

Eratosthenes used Syene and Alexandria for his experiment, which were approximately 5000 stadia apart (about 925 kilometers).

What was the significance of the shadow observed in Alexandria?

The shadow observed in Alexandria showed that the Sun was not directly overhead as it was in Syene. This difference in shadow length helped Eratosthenes calculate the angle of the Earth's curvature and, in turn, its circumference.

What was the angle of the shadow in Alexandria during Eratosthenes' experiment?

The angle of the shadow in Alexandria was measured to be 7.2 degrees.

How did Eratosthenes use the angle of the shadow to calculate the Earth's circumference?

Eratosthenes realized that the angle of the shadow (7.2 degrees) corresponded to a fraction of the Earth's 360 degrees. He used this ratio (7.2/360) and the distance between the two cities (5000 stadia) to calculate the Earth’s total circumference.

What was Eratosthenes' calculated value for the Earth's circumference in stadia?

Eratosthenes calculated the Earth's circumference to be about 250,000 stadia.

How accurate was Eratosthenes' calculation of the Earth's circumference compared to modern measurements?

Eratosthenes' calculation was remarkably accurate. His result, when converted to modern units, was approximately 40,125 kilometers, which is very close to the modern value of 40,075 kilometers for the Earth's circumference.

What is the modern equivalent of one stadia, as used by Eratosthenes in his calculations?

One stadia, in the context of Eratosthenes’ calculations, is approximately 185 meters.