How did scientists back in the middle ages measure the diameter of planet earth while on earth?

Answer 1

Erathosthenes was the first one to measure it.

Answer 2

The previous two answers are correct, but they forget an important detail.

You asked for the Middle Ages. In the Dark Ages, after the fall of the Roman Empire that information and a lot of other were lost. In fact as part of the Dark Ages scientific information and research was suppressed! In the Middle Ages the world was thought to be FLAT! Remember that people feared Chris Columbus would sail off the edge of the world!

The diameter of the earth can be measured on the planet by observing the horizon. The Greeks had the closest figure and arrived at it by watching a ship sailing into the harbor. As the ship appeared the distance was calculated from the observer which told the observer how much curvature there was in the Earth and therefore it was a sphere and so its diameter could be calculated.

In the Dark Ages all that was lost, despite the teaching of the Christian Church that Classical Greek science was the best science and so sponsored by the Church.

Because of this attitude new research was discouraged and suppressed. It wasn’t until the Renaissance that science was again embraced and allowed to continue. If it weren’t for the Dark Ages we could already have colonies on Mars.

The Church demanded to be the absolute power in Europe and as such it couldn’t be wrong. Even when Galileo showed the moons of Jupiter to the Church officials they still refused to allow the teaching that the earth was not at the center of the universe. They didn’t ignore what was as plain as the nose on your face; they just suppressed it saying that the public wasn’t ready for that information (which in a way is even worse). When Galileo refused to stay quiet about it he was condemned to home arrest for over 300 years (Pope John Paul pardoned him before the pope’s death). The Christian Church has a pattern and principle of working against science; even when the science is as plain as the nose on my face. This is one of the major failings of the modern church. I don’t say that there should be no limits on science, but we need reasonable ones.

Answer 3

They stood up and got counted!

Techniques for reaching conclusions of foreign objects such as the diameter were drawn up by the distance between shadows and length or object in view.
During summer months shadows were shorter in winter they were longer - using this as a basis they walked the earth and calculated by rule of thumb. Other methods were done on foot - thus the introductions of measurements in inches (thumb length), hands (still used as measurment for horses height), arms, feet and the yard that was used to perform the experimental measurements. Having a set bed of figures they could be used to measure almost anything.

Answer 4

Actually, it was done way before that by the Egyptians in about 200BC (not exactly sure about the date)

Eratosthenes (a librarian in Alexandria) measured the angle of light coming into 2 different cities at the same time during the day. With simple geometry, he calculated the circumference of the earth