Who calculated the diameter of the Earth?

Question

He also calculated the diameter of the equator and the south and north pole.

Answer 1

The Egyptian Eratosthenes, director of the Library in Alexandria, wedded observation to calculation. His idea was as simple as it was brilliant. When the sun was directly above Aswan, 500 miles away, he measured the shadow cast by a vertical tower in Alexandria. The rest was simple trigonometry. He calculated earth's diameter with only 16 percent error, and his method was used right down to modern times.

Answer 2

The diameter of the Earth at the equator is 12,756 kilometers (km).

How Do We Calculate Distances of This Magnitude?
Clementine image of Earth - false color In 200 B.C., the size of the Earth was actually calculated to within 1% accuracy! Eratosthenes used Aristotle's idea that, if the Earth was round, distant stars in the night sky would appear at different positions to observers at different latitudes. Eratosthenes knew that on the summer solstice, the Sun passed directly overhead at Syene, Egypt. At midday of the same day, he measured the angular displacement of the Sun from overhead at the city of Alexandria - 5000 stadia away from Syene. He found that the angular displacement was 7.2 degrees - there are 360 degrees in a circle, making 7.2 degrees equivalent to 1/50 of a circle. Geometry tells us that the ratio of 1/50 is the same as the ratio of the distance between Syene and Alexandria to the total circumference of the Earth. Thus the circumference can be estimated by multiplying the distance between the two cities, 5000 stadia, by 50, equaling 250,000 stadia.

math equation

How do we convert to kilometers? Well, we believe that the unit of the "stadium" was about 0.15 km. This means that Eratosthenes estimated the circumference of the Earth to be about 40,000 km.

So how did Eratosthenes do compared to modern measurements? Well, the Earth is almost, but not quite, a perfect sphere, which is what Eratosthenes assumed. The Earth is actually slightly flattened. The measured circumference around the equator is 40,075 km, which is longer than the circumference through the poles of 40,008 km. Eratosthenes was measuring the latter, and got it almost exactly right. We're not sure the exact conversion factor from stadium to km, so we don't know exactly how close his number was to the modern value.

http://heasarc.gsfc.nasa.gov/docs/cosmic/earth_info.html

Answer 3

In 200 B.C., the size of the Earth was calculated by Eratosthenes to within 1% accuracy.

Answer 4

Eratosthenes

Answer 5

“Journal du Voyage fait par l’ordre du Roi a L’equateur”, published in 1751, and the maps made by Charles Marie de La Condorine

Answer 6

Eratosthenes, a greek librarian

Answer 7

eratosthenes. using the concepts of trigonometry.

Answer 8

not me