how did they calculate the circumference of the earth

His method was so simple that he just used sticks and geometry (and a poor guy) to determine the circumference of the earth. Eratosthenes died around 194 B.C. There, he became known for his achievements in many different fields, including poetry, astronomy, and scientific writing. Eratosthenes of Cyrene was a Greek polymath: a mathematician, geographer, poet, astronomer, and music theorist. But many scholars think it likely that he was using the Egyptian stadia (157.5 m), being in Egypt at the time.

A man named Posidonius copied Eratosthenes' basic method about a century later, using the star Canopus, Rhodes, and Alexandria as starting points. If that was the case, then using his formula, the earth was 250,000stadia around. Syene sat to the south of Alexandria. Eratosthenes described his technique in a book entitled On the measure of the Earth, which has not been preserved. He also wrote the poem Hermes, correctly sketched the route of the Nile, and even gave a more-or-less accurate account of why the Nile flooded, something that had baffled scholars for centuries. Due to the uncertain distance that stadia represents (and particularly which stadia he was using), historians believe that Eratosthenes' conclusion was between .5% and 17% off the mark. The measure of Earth's circumference is the most famous among the results obtained by Eratosthenes, who estimated that the meridian has a length of 252,000 stadia, with an error on the real value between -2.4% and +0.8% (assuming a value for the stadion between 155 and 160 metres).

Eratosthenes' most recognized milestone was his impressive calculation of the Earth’s circumference.

Furthermore, he knew that a circle contained 360°, which meant that his calculation—7°14'—was roughly one fiftieth of a circle.

At high noon, the sun would shine directly overhead and there would be no shadows stemming from the columns. Being a good mathematician, he decided to use this knowledge to do a few calculations to figure out the circumference of the Earth.

They knew about central angles and arcs. He was a man of learning, becoming the chief librarian at the Library of Alexandria.

in Cyrene, Libya, Eratosthenes soon became one of the most famous mathematicians of his time.

However, he didn't measure the distance between Rhodes and Alexandria correctly, resulting in a circumference that was smaller than Eratosthenes' estimation. Whatever the case, he estimated the distance between Syene and Alexandria was 5,000 stadia. Born around 276 B.C. The missing information was simply how far away Syene was from Alexandria.

If you liked this article, you might also enjoy: Emily Upton writes for the wildly popular interesting fact website TodayIFoundOut.com. Nevertheless, it provided a precursor for maps we know today.

To do this, Eratosthenes measured the shadow of an obelisk on June 21 at noon. He calculated the Earth’s tilt with remarkable accuracy, but also inaccurately measured the distance between Earth and the Moon. knew how to measure circumference.

His work is comparable to what is now known as the study of geography, and he introduced some of the terminology still used today. The greek way – 240 BC The very first person to determine the circumference of the earth was Eratosthenes, in sometime around 240 BC.

Second, that he heard a camel could travel 100 stadia a day, and it took a camel about 50 days to travel to Syene. It all started when he was peacefully reading something at the library of Alexandria.

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He measured the distance in stadia. He worked on a calendar that included leap years and he also estimated and corrected the dates of various historical events beginning with the Siege of Troy.

(And, yes, people at that point had known for some time that the world wasn't flat, contrary to popular belief.).

Turns out many different people considered a stadia to be different lengths, so we are not 100% sure Aristotle meant the modern value we find. Eratosthenes was able to rub shoulders with the likes of Archimedes while continuing his own learning. One complete trip around earth (one rotation) is 360°, so any arc of the circle or sphere is a fractional slice of 360°. Total Circumference of the Earth= ((360/7.2) x D) kilometers The unit of measurement that was popular in Greece at the time was stadia. His activities became so talked about, in fact, that Ptolemy III of Egypt decided to invite him to Alexandria to tutor his son.

Therefore, Aristotle had the Earth’s circumference at about 39,146 miles, assuming this was the stadia he referenced. While finding the approximate circumference of the Earth was probably Eratosthenes' largest contribution to scholarship at the time, it was by no means the only one. While finding the approximate circumference of the Earth was probably Eratosthenes' largest contribution to scholarship at the time, it was by no means the only one. Despite these accomplishments and many more like them, Eratosthenes was often nicknamed "Beta." There isn't an exact modern day conversion to stadia, and it isn't perfectly clear which version of the stadia Eratosthenes was using, but regardless, from what is known, his estimation was remarkably accurate. They knew the circumference of a sphere formula, 2πr. Eratosthenes is considered the inventor geography, particularly because he developed the system of latitudinal and longitudinal lines to map the world. So he multiplied 500 by 50 to arrive at his estimate of the Earth’s circumference: 25,000 miles. People in 240 B.C.E. There had been previous attempts at discovering the Earth's circumference (which don't count as "first recorded" because their methods didn't survive, though we have references to them) which resulted in a 400,000 stadia figure, 150,000 more than Eratosthenes'—obviously far from accurate.

To subscribe to Today I Found Out's "Daily Knowledge" newsletter, click here or like them on Facebook here. He discovered that the sun was about 7°14' from being directly overhead. Historians have yet to figure out the true length of a single stadia, but popular estimates put it around 160 meters. Therefore, Eratosthenes thought, if he multiplied the distance between Syene and Alexandria by 50, he would have the circumference of the Earth. Not only that, but Eratosthenes estimated the distance to both the sun and the moon, and measured the tilt of the Earth's axis all with amazing accuracy. Beta is the second letter in the Greek alphabet and referred to Eratosthenes being second-best in everything he did. Eratosthenes thought the following way. He realized that, because the Earth is curved, the greater the curve, the longer the shadows would be.

However, Eratosthenes realized that at the same moment in Alexandria, columns clearly did have shadows. The Library of Alexandria was a hub of learning at the time, attracting scholars from across the known world. Well, the difference in angle between these two cities is equal to 7.12°, which is 50.56 times less than a full circle. Eratosthenes was able to accomplish this in part because of his education in Athens.

It is believed that he started going blind in his later years and, unable to continue his work, he simply stopped eating.

There are two theories as to how Eratosthenes figured out the distance: first, that he hired a man to walk there and count the steps.

While determining how to calculate the size of the Earth, Eratosthenes became aware of a well in Syene (modern-day Aswan, Egyp… However, these lines were irregular and often drawn through known places, meaning they weren't entirely accurate.

This would make his estimate only about 1% too small. Though none of Eratosthenes' personal work on the sieve survives, he was credited with the creation of the algorithm by Nicomedes in his Introduction to Arithmetic.

and is thought to have starved himself to death. The mathematician must have been thrilled to have this opportunity. This estimate was only 100 miles off the actual circumference of 24,900 miles!

Even if the latter case was true, it was astoundingly accurate given the limited technology he was dealing with at the time. Later, he would become the head librarian of the Library of Alexandria. Based on his observations, he hypothesized that Syene must lie 7°14' along a curve from Alexandria. It was probably in the Library of Alexandria that he read about a curious event that took place in Syene (now Aswan, Egypt) at the summer solstice. He is also remembered for the Sieve of Eratosthenes, a simple algorithm that makes it easy to find all prime numbers up to a certain limit. But how did he know it was noon in Alexandria? It was this circumference that was recorded by Ptolemy in his geography treatise and later used by explorers looking for a quicker way to the Indies. This post has been republished with permission from TodayIFoundOut.com. You can also check 'em out on YouTube here. Eratosthenes is also credited with coming up with a way to map out the known world by drawing lines north-south and east-west—early latitude and longitude lines. Eratosthenes divided 360° by 7.2° and got 50, which told him that the distance between Alexandria and Syene (500 miles) was 1/50 of the total distance around the Earth. He is best known for making the first recorded measurement of the Earth's circumference, which was also remarkably accurate.

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