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- To measure the circumference of the Earth, you can use several methods
To measure the circumference of the Earth, you can use several methods
This ancient problem is no longer a challenge today, thanks to precise measuring instruments. In 240 BCE, the Greek mathematician Eratosthenes applied a clever method to calculate the circumference of the Earth. Eratosthenes observed the shadow cast by a vertical pillar in Alexandria, Egypt, at noon during the summer solstice. The angle of incidence was measured to be 7.2 degrees. Simultaneously, at a location 500 miles (approximately 800 kilometers) southeast from Alexandria, sunlight shone directly to the bottom of a well. Please refer to the diagram below.
[Diagram illustrating Eratosthenes' method of measuring Earth's circumference]
Using this information, Eratosthenes was able to estimate the Earth’s circumference.
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In the diagram, point C represents the location of the well, point A represents the location of the vertical pillar in Alexandria, and point O represents the center of the Earth. It is given that AOC is a right angle, and the arc AC has a length of 500 miles. Assuming the circumference of the Earth is denoted by s, we can calculate it using proportions. Thus, s = 500 × 50 = 25,000 miles, which is approximately 40,232.5 kilometers.
