The first recorded use of the word geography was by Eratosthenes, a Greek scholar who lived from 276–194 BC who is credited with creating the discipline of geography. Geography is thought to have originated with the ancient Greeks. It was the Greeks who showed the first interest in the size and shape of the Earth.
Eratosthenes was a Greek expert in many disciplines, including astronomy, geography, and mathematics. He is most famous for his calculation of Earth’s circumference and for inventing the word geography.
Having heard of a deep well at Syene (near the Tropic of Cancer and modern-day Aswan) where sunlight only struck the bottom of the well on the summer solstice, Eratosthenes worked out a method by which he could calculate the circumference of the earth using basic geometry. (Greek scholars knew that the earth was indeed a sphere.) The fact that Eratosthenes was a close friend of the famous Greek mathematician Archimedes is perhaps one reason for his success in this calculation. If he did not collaborate directly with Archimedes in this exercise, he must have certainly been helped by his friendship with the great pioneer in geometry and physics.
To calculate the circumference of the earth, Eratosthenes needed two critical measurements. He knew the approximate distance between Syene and Alexandria, as measured by camel-powered trade caravans. He then measured the angle of the shadow in Alexandria on the solstice. By taking the angle of the shadow (7°12′) and dividing it into the 360 degrees of a circle (360 divided by 7.2 yields 50), Eratosthenes could then multiply the distance between Alexandria and Syene by 50 to determine the circumference of the earth.
Remarkably, Eratosthenes determined the circumference to be 25,000 miles, just 100 miles over the actual circumference at the equator (24,901 miles). Although Eratosthenes made mathematical errors in his calculations, these fortunately canceled each other out and yielded an amazingly accurate answer that still causes scientists to marvel.
A few decades later, the Greek geographer Posidonius insisted that Eratosthenes’ circumference was too large. He calculated the circumference on his own and obtained a figure of 18,000 miles–7,000 miles too short. During the middle ages, most scholars accepted Eratosthenes’ circumference, though Christopher Columbus used Posidonius’ circumference to convince his supporters that he could quickly reach Asia by sailing west from Europe. As we now know, this was a critical error on Columbus’ part. Had he used Eratosthenes’ figure instead, Columbus would have known he was not yet to Asia when he landed in the New World.
Eratosthenes was born around 276 BCE at a Greek colony in Cyrene, territory lying in what is present-day Libya. He was educated at the academies of Athens and was appointed to run the Great Library at Alexandria in 245 BCE by Pharoah Ptolemy III. While serving as head librarian and scholar, Eratosthenes wrote a comprehensive treatise about the world, called Geography. This was the first use of the word, which in Greek literally means “writing about the earth.” Geography also introduced the concepts of torrid, temperate and frigid climate zones.
In this work, the contents of which are known because of references from subsequent books still in existence, Eratosthenes divided the planet into climate zones and employed overlapping grid lines onto maps of Earth. Geographika also listed the names and locations of 400 cities.
He created an algorithm for determining prime numbers that is still in use today. It still bears his name: the Sieve of Eratosthenes. He used his mathematical knowledge and his geographical curiosity to perform his most famous experiment, the determination of Earth’s circumference, in 240 B.C.
Eratosthenes knew that at a well in Egypt, near Swenet (in Greek Syene and today Aswan), the Sun appeared directly overhead at precisely noon. He wasn’t at the well when he made his calculation, however; rather, he was in Alexandria, where he was serving as head of the Great Library. He measured the angle of elevation of the Sun at noon in Alexandria and came up with a result of 1/50th south of the zenith. Alexandria was due north of Swenet, and Eratosthenes calculated that the distance between the two places was 1/50th of a circle’s circumference, or 1/50th of 360 degrees, or 7 degrees and 12 minutes.
Employing the distance between the two cities as 5,000 stadia (a distance known to many who traveled between the two cities), he then multipled that figure, 5,000, by 50 (360 divided 7.12) and got 250,000 stadia. A stadion in ancient Greece was thought to be the equivalent of 600 feet today, so 250,000 stadia was 150 million feet. That was Eratosthenes’ estimate of Earth’s circumference.
The real distance is 24,859 miles, or 131,259,849 feet. Eratosthenes wasn’t too far wrong, and he didn’t have the fancy instruments that geographers have today.
His other geographical accomplishments include reasonably accurate measurements of the tilt of Earth’s axis, the distance from Earth to the Moon, and the distance from Earth to the Sun.
There is still more. Eratosthenes also contributed to geographic source of the river. Many scholars that preceded Eratosthenes in the study of the Nile river, tried to figure out the reason why parts of the river flooded while other parts did not. It was not until Eratosthenes that a correct answer was proposed. He believed that heavy rains near the source of the Nile was the cause of Many of Eratosthenes’ peers nicknamed him “Beta” which is the second letter of the Greek alphabet, indicating that he just fell short of first place. Eratosthenes contributed greatly to many different areas of knowledge, more than I could cover in this short paper. Maybe in his time period, his peers did not feel that he contributed enough in one area or maybe they were jealous that he had contributed so much to so many areas. For a man who was nicknamed Beta, it is pretty impressive that so much of his work in these areas is still discussed today, so many years later.
He wrote other books, including Chronographies, a scientific analysis of historical dates; Olympic Victors, a chronological listing of winners at the Olympics; works on grammar and rhetoric; and even plays and poems. He also essentially invented the leap day and year, using predictions about planetary movements.
He died in 194 B.C., at age 82.