Early Efforts to Measure the Circumference of the Earth

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Science and technology is intertwined with the advancement of the human condition. The problems that men and women face on Earth demand solutions, and the solutions to these problems often have farther reaching implications than the original task they were built for. From the wheel to the iPad each new bit of knowledge has been made possible because of the work and brain power of those gone before; many different areas of research are affected by the advances in technologies around the world.

One of these areas where technological and scientific advancement has benefited more than the original creators is navigation and measurement. The tools that we associate with this topic include telescopes, sun dials, compasses, and cartography equipment that can measure the distances between objects. These navigational tools were designed to help early sailors be able to travel the oceans without having to be in sight of land to know where they were, and then to help map parts of the world that hadn’t been explored yet. In the modern day navigation still benefits from the information gathered by these technologies, with the added perk of having the majority of these tools computerized using software programs and information gathered by satellite.

Measuring the Earth and distances between places doesn’t just help us when we’re going on a road trip and need GPS. For centuries individuals have been creating ways to accurately measure various aspects of the Earth using the tools of their times. Aristotle, Archimedes, Erastosthenes, and Caliph al-Mamun are just a few of the early scientists who built the foundations of the field of geodesy, or the science of measuring and representing the Earth. They contributed so much information to the knowledge of the time about the world around us that has led modern man to technologies above and beyond what they could have imagined.

The idea of a spherical Earth was one of many ideas thrown about in ancient Greece when other thoughts about the Earth’s form (including that it was flat or rectangular) were also under discussion. Pythagoras, the father of the Pythagoras theorem and a brilliant mathematician, was supported in his spherical Earth belief by Aristotle. The Greeks eventually adopted a common view that the Earth was indeed spherical and study began to determine just how big it actually was.

Speculation about the Earth’s size ranged from guesses to more mathematically correct estimations. Plato took a guess at Earth’s circumference at 62,800-74,000 kilometers (or 39,250-46,250 miles) while Archimedes was closer with a guess of 55,500 kilometers, or 34,687 miles. Archimedes was the closest to guessing the accurate circumference of the Earth, which is 40,075 kilometers. Erastosthenes, a Greek scholar living in Egypt, observed the position of the sun during the summer solstice and calculated the approximate circumference of the Earth using the distances between Egyptian cities. His guess was approximately 25,000 miles which was the closest estimate to Earth’s actual circumference of 24,902 miles.

Eratosthenes' method for determining the size of the Earth. Source: Geodesy for the Layman, 1984.
Eratosthenes’ method for determining the size of the Earth. Source: Geodesy for the Layman, 1984.

Scientific studies conducted around the world from the Middle East to China, India to Europe all had their scholars who attempted to discern the size of the Earth. Middle Eastern scholars included Caliph al-Mamun in AD 830 who furthered the navigational sciences through his work measuring the distances between cities and determining their latitudinal significance in the greater scheme of the Earth. Through their study they were able to determine the placement of cities, calculate the distance between them, and place these calculations on other parts of the world to create a better understanding of the size of the Earth. Muslim scientists and astronomers first commissioned their research into geodesy because of the importance of the city of Mecca, and the necessity of knowing which direction to pray to from various parts of the world.

Measuring the circumference of the Earth was of obvious importance for civilizations around the world. Every society regardless of technological ability or scientific prowess was infinitely curious about the world around them and understanding how they geographically fit into the bigger picture of life on this spinning blue planet. Understanding the size of Earth and its circumference helped early civilizations be able to visualize a bigger world while still being able to improve their place in it.

References

Sharp, Tim. How Big is Earth? 17 September 2012. Web access 28 November 2014.

Geodesy for the Layman.  1984 . United States Air Force.  Web access 28 November 2014.

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