Do Now:Write three pieces of

evidence that told us that the earth was round.

Aim: How do we measure the shape and size of the earth?

Topic: Unit 1Main Idea: Eratosthenes’s Method

1) What is the true shape of the earth?

The earth is a slightly flattened sphere called an

“oblate spheroid”.

Observations of the shape of the horizon, how ships disappear and lunar eclipses.

2) How do we know about the shape of the earth?

He was able to calculate the circumference (distance around) the earth with great accuracy.

3) What did Eratosthenes discover about the earth?

The height of the sun decreases as you move away from the equator.

4) What happens to the angle of the sun as you travel north or

south of the equator?

Angle of the sun = distance

360o circumference

or

Circumference= (360 )(distance)

angle

5) What formula did he use?

24,901 mi – 24,662 mi X 100 24,901 mi 239mi X 100 24,901 mi

0.96% !!!

6) Eratosthenes calculated the circumference of the earth to be 24,662 km while it is actually 24,901 mi. What was his

percent deviation?

(360o)(2 km) (9o)

720o.km

9o

80 km

Summary:A new planet is discovered and measurements using

Eratosthenes’s method are as follows: distance (S) = 2 km angle (L) = 9 degrees. Calculate the circumference of the new planet.