Eratosthenes
was a well-known Ancient Greek Alexandrian scholar often referred to as the
“father of geography” for his exceptional findings, specifically regarding the
earth. He was born in Cyrene, Libya
around 276 B.C.E. Eratosthenes was most recognized in his work within the
fields of astronomy, mathematics, history and philosophy.
Eratosthenes
was initially a head librarian and scholar, and this is the era when
Eratosthenes wrote a treatise about the world, called Geography. This is where the term geography
originated. Geography is a Greek term
meaning "writing about the earth" in literal terms. His work Geography also introduced the climatic concepts of
torrid, temperate, and frigid zones.
He created many reports
from different travellers and explorers in order to describe the physical
features of each region. He described
these regions through the action of natural phenomena such as water, fire,
earthquakes and volcanic eruptions.
Eratosthenes
was most notable for his determination of attempting to discover the
circumference of the earth. Being a
Greek philosopher, he knew that the earth indeed was a sphere. In order to calculate the circumference of
the earth, Eratosthenes calculated the approximate distance between Syene and
Alexandria by camel-powered trade caravans. Then, he measured the angle of the
shadow in Alexandria on the solstice. He took the angle of the shadow (7°12')
and divided it into the 360 degrees of a circle. The equation was 360 divided by 7.2
yields. He then multiplied the distance
between Alexandria and Syene by 50 to determine the overall circumference. Eratosthenes came to the conclusion that the circumference is
25,000 miles, which is only 100 miles over the actual circumference at the
equator which is converted into 40,000
kilometres which is 250,000 stadia.
This diagram
illustrates the cross-section of the Earth, at noon, on the
northern hemisphere's summer solstice. Eratosthenes
used this information to calculate the circumference of the earth.
However,
Eratosthenes’s calculations were not as accurate as he made it seem. A Greek geographer named Posidonius believed
that Eratosthenes' circumference was too large. He conducted a calculation of
the circumference on his own, and ended up getting the result of 18,000 miles,
which was 7,000 miles too short.
Eratosthenes
also came up with his own method for charting the Earth’s surface. The way he
categorized it was by separating the world known to him into a Northern and Southern
division by using an east–west line parallel to the equator running through the
island of Rhodes, and dividing the Mediterranean. He then added a second
north–south line at right angles running through Alexandria. Eratosthenes also drew
additional east–west as well as north–south lines to his map.
This illustrates Eratosthenes’
method for calculating the circumference of the earth by by calculating the distance
between these two points. This allowed Eratosthenes
to calculate the curvature of the earth between the two points and figure out
how to apply the information to calculate the circumference of the earth.
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