1. Aim: How do we know the true shape of Earth?
Do Now: Describe the shape of Earth using your own terms.

2. Do You Think the World is Flat?
World Map Click Me

3. Do you think the Earth is flat? How do you know?

4. How can you prove that the earth is round?

5. How can we prove earth is not flat?
Evidence from Space
1. Photographs taken from outer space.
Earth looks perfectly round and smooth

6. How can we prove earth is not flat?
2. Earth has a curved surface - when a ship sails farther away from you, the ship “appears” to sink
Ships mast first to appear and last to disappear over the horizon

7. How can we prove earth is not flat?
3. When a lunar eclipse occurs, (eclipse of the moon) the shadow of the earth has a curved circular pattern.
Dec 21, 2010 lunar eclipse

8. How can we prove earth is not flat?
There is also evidence of Earth’s shape in the observation of distant objects in the night sky. A person at the North pole sees the North Star, Polaris, directly overhead. To a person located farther south, Polaris appears lower in the sky. In fact, at the equator, Polaris is located along the horizon. South of the equator, Polaris is not visible at all. The height (altitude) of Polaris in the night sky is equal to the latitude of the observer which is consistent with a spherical earth.
How can we prove earth is not flat?
4. Changing of the position the Sun and North Star, Polaris
North Star (Polaris) – The altitude of Polaris is equal to the latitude (northern hemisphere)
The North Star cannot be seen in the southern hemisphere

9. What is the true shape of Earth?
Oblate spheroid –
Earth is slightly flattened at the poles and bulging (wider), at the equator
Due to Earth’s rotation
Earth’s dimensions
Circumference at the Equator = 40,074 km
Equatorial diameter – 12,756 km
Circumference at the Poles = 40,007 km
Polar diameter – 12,714 km

10. How do gravity measurements explain earth’s true shape?
A person at the North Pole will weigh more because the poles are slightly flatten and are closer to the center of the earth (more gravity)
A person at the Equator will weigh less because the equator bulges (wider) and is farther from the center of the earth (less gravity)

11. Summary Activity How do you know that the earth is not flat?
How do we know the true shape of Earth?
Compared to the weight of a person at the North Pole, how would the weight of a person at the equator be different? Why?

12. Summary Questions

13. Summary Questions