Unit 1 Earth’s Dimensions The Earth has an Oblate Spheroid Shape Polar Circumference= 40,008 km Equatorial Circ. = 40,076 km Polar Diameter = 12, 714 km Equatorial Diameter= 12, 757km

The Geographic poles are at the ends of the Earth’s Axis of Rotation. The axis is tilted at an angle of 23 ½ degrees

Although the Earth is not a perfect sphere it is very close as compared to the size of its diameter. The Earth has very little relief compared to its diameter. If you compare the highest mountain to the deepest ocean we find that the Earth is smooth.

EXAMPLE Mount Everest is 9km high The Marinas Trench is 11km deep 20 km as compared to 12, 757km less than 0.2% of the diameter On a normal 20cm globe Mt Everest would be 1/10th of a millimeter.

Evidence of the Earth’s Shape 1. Altitude to Polaris(North Star)- is located directly over the Earth’s Axis of Rotation. Therefore the angle above the horizon to Polaris in the northern hemisphere is equal to the observer’s latitude

The altitude to Polaris at any place in the Northern Hemisphere is equal to it’s latitude. The latitude at any given point on the Earth is equal to the angle from the equator to a radius line that extends to the point on the surface

2. Lunar Eclipses- The shadow of the Earth cast on the moon’s surface is round.

During a lunar eclipse the Earth’s curved shadow is cast on the moon.

3. Gravity Measurement- gravity is the force that pulls all objects toward the center of the Earth. Weight = mass x gravity Describe how this can be used to determine the shape of the Earth

As you move away from the Earth gravity decreases. The distance from the center of the Earth to the poles is less than the distance to the equator, Therefore gravity is greater at the poles.

4. As an observer on shore watches a ship sail out to sea the ship will appear to sink into the sea as it passes over the horizon. This occurs due to the ship following the curvature of the Earth. Observer Ship Observer’s Line of Sight

5. Photographs from space are the best evidence of the Earth’s shape.

Proofs of the Earth’s Shape Pictures of the Earth from Space Other Objects in the Sky Lunar Eclipse Ships Sailing Out to Sea The Changing Altitude of Polaris The Change in Gravity on Earth Distance Between Adjacent Lines of Latitude

Earth’ Motions Earth rotates on its axis at a rate of 15 ⁰ per hour. Earth’s rotation causes the apparent motion of the sun They appear to revolve around the Earth, but it doesn’t the Earth is moving around the sun

All the stars seem to rotate around Polaris throughout the night. The pattern of stars also change throughout the year. They also move around Polaris.

Circumpolar Star Trails

Proofs of the Earth’s Rotation Motion of a Foucault Pendulum –Jean Foucault Coriolis Effect –Deflection in the Northern Hemisphere –Deflection in the Southern Hemisphere

Foucault Pendulum at the United Nations

Sun Winter Orion Summer Sagittarius Earth

Orion Winter Constellation in the Southern Sky

Sagittarius - Summer Constellation in the Southern Sky