1. PowerPoint Presentation
Mr. Syracuse
PowerPoint Presentation
Copyright 2008, All rights reserved

2. Eratosthenes’ Method

3. Eratosthenes of Cyreneβ
Eratosthenes of Cyrene
B.C.E.

4. The known world in 194 B.C.E.

5. Ancient Library of Alexandria

6. Modern Library of Alexandria

7. Modern Library of Alexandria

8. Ancient unit of measurement – the Stade
Stadium name
Length (approximate)
Itinerary
157 m
Olympic
176 m
Attic/Italic
185 m
Babylonian-Persian
196 m
Phoenician-Egyptian
209 m

9. How big is the
Earth?

10. Look to the sun for the answer!
Obelisk in
Alexandria
Sun
Earth
Well in Syene

11. θ What Eratosthenes noticed Sunlight was at an angle in Alexandria…
…And right overhead in Syene. θ

12. How could this be explained?
Center – O – the earth θ θ

14. θ 360° Distance Circumference =
We can get a simple formula!
Part of a circle in relation
to the whole circle… θ
360°
Distance
Circumference =
…Part of the circumference in relation
to the whole circumference.

15. So how big is the earth?
Eratosthenes figured out that θ was 7.2°
He knew the distance was 5,000 stadia
Just plug and chug to find the circumference!
He got 39,690 km. How far off is that?