How did early astronomers figure out how large the Earth really was?
Thank you! :-)
Yes, see here:
http://www.astro.washington.edu/courses/labs/eratosthenes/rung1.html
The ancient Greeks also measured the distance to the Moon:
http://www.astro.washington.edu/courses/labs/eratosthenes/rung2.html
They also attempted to measure the distance to the Sun:
http://www.astro.washington.edu/courses/labs/eratosthenes/rung3.html
but they could not obtain a accurate figure for this.
Check this article.
http://en.wikipedia.org/wiki/History_of_geodesy
Early astronomers figured out the size of the Earth using a method called "geodesy." Geodesy is the science of measuring the shape, size, and gravity field of the Earth. One of the most significant contributions to determining the Earth's size was made by the ancient Greek philosopher and mathematician Eratosthenes in the 3rd century BCE.
Eratosthenes used a simple yet ingenious method involving the observation of shadows. He realized that if he measured the angle of the shadow cast by a vertical stick at noon in two different locations on the Earth, he could determine the curvature of the Earth's surface between those two locations.
To perform this measurement, Eratosthenes chose two cities in Egypt, Alexandria, and Syene (now Aswan), located approximately 800 kilometers apart. On a specific day at noon, he measured the length of the shadow cast by a stick in Alexandria and found it to be about 1/8th the length of the stick itself (roughly 7.2 degrees angle). At the same time, in Syene, he found that a stick cast no shadow at all, indicating the Sun was directly overhead (0-degree angle).
By comparing the two angles, Eratosthenes concluded that the distance between Alexandria and Syene represented approximately 1/50th of the Earth's total circumference. Since he knew the actual distance between these two cities, he was able to estimate the Earth's circumference by using simple proportion.
His calculations resulted in a remarkably close approximation of the Earth's size, giving a circumference of approximately 39,375 kilometers. Although this estimate was not entirely accurate, considering the technology and methods available at the time, it was a significant achievement in determining the Earth's size.
Overall, early astronomers like Eratosthenes used careful observation, measurements, and mathematical calculations to understand and quantify the size of the Earth.