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

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

How can you prove that the earth is round?

Evidence from Space 1. Photographs taken from outer space. –Earth looks perfectly round and smooth 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 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. How can we prove earth is not flat? Dec 21, 2010 lunar eclipse

4. Changing of the position the Sun and North Star, Polaris North Star (Polaris) – The angle of Polaris is equal to the latitude (northern hemisphere) The North Star cannot be seen in the southern hemisphere 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.

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 kmCircumference at the Equator = 40,074 km Equatorial diameter – 12,756 kmEquatorial diameter – 12,756 km Circumference at the Poles = 40,007 kmCircumference at the Poles = 40,007 km Polar diameter – 12,714 kmPolar diameter – 12,714 km

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)

Summary Activity 1.How do you know that the earth is not flat? 2.How do we know the true shape of Earth? 3.Compared to the weight of a person at the North Pole, how would the weight of a person at the equator be different? Why?

Summary Questions