Presentation of Eratothenes and its calculation for circumference of the Earth

1. Eratosthene
s
Paraskevi Evangelou
2016-17
Erasmus +

2. Who was Eratosthenes?
 Eratosthenes (276 BC- 194 BC) was a Greek
mathematician, geographer, poet, astronomer,
and music theorist.
 He was a man of learning, becoming the chief
librarian at the Library of Alexandria.
 He invented the discipline of geography,
including the terminology used today.

3. Also…
 He is best known for being the first person to
calculate the circumference of the Earth, which he
did by applying a measuring system using stadia, a
standard unit of measure during that time period.
 His calculation was remarkably accurate. He was
also the first to calculate the tilt of the Earth's axis
(again with remarkable accuracy).
 Additionally, he may have accurately calculated the
distance from the Earth to the Sun and invented the
leap day.
 He created the first map of the world, incorporating
parallels and meridians based on the available
geographic knowledge of his era.

6. Measurement of the Earth's
circumference
 Eratosthenes calculated the circumference of the Earth without
leaving Egypt.
 He knew that at local noon on the summer solstice in Syene
(modern Aswan, Egypt), the Sun was directly overhead. He
knew this because the shadow of someone looking down a
deep well at that time in Syene blocked the reflection of the Sun
on the water.
 He measured the Sun's angle of elevation at noon on the same
day in Alexandria.
 The method of measurement was to make a scale drawing of
that triangle which included a right angle between a vertical rod
and its shadow.
 This turned out to be 1/50th of a circle. Taking the Earth as
spherical, and knowing both the distance and direction of
Syene, he concluded that the Earth's circumference was fifty
times that distance.

9.  His knowledge of the size of Egypt was founded on the work of many
generations of surveying trips. Pharaonic bookkeepers gave a distance
between Syene and Alexandria of 5,000 stadia.
 Some say that the distance was corroborated by inquiring about the
time that it took to travel from Syene to Alexandria by camel.
 Others say that Eratosthenes paid a man to walk and measure the
distance.
 Some claim Eratosthenes used the Olympic stade of 176.4 m, which
would imply a circumference of 44,100 km, an error of 10%, but the
184.8 m Italian stade became (300 years later) the most commonly
accepted value for the length of the stade, which implies a
circumference of 46,100 km, an error of 15%.
 It was unlikely, even accounting for his extremely primitive measuring
tools, that Eratosthenes could have calculated an accurate
measurement for the circumference of the Earth.
He made two important assumptions (neither of which is perfectly
accurate):
 That the distance between Alexandria and Syene was 5,000 stades,
 That the Earth was a perfect sphere.

12. VIDEO

13. THE END
THANK YOU FOR WATCHING!