Unit 1: Earth’s Dimensions

Unit 1: Earth’s Dimensions

Earth’s Shape

What is the shape of the Earth?

Earth is NOT a perfect sphere, but it IS close!

The true shape of Earth is an oblate spheroid.

This means that Earth’s equatorial diameter is slightly larger than its polar diameter.

Evidence of Earth’s Shape

1. Photographs of Earth from outer space show that Earth is round

2. Years ago, sailors noticed that ships slowly disappeared or appeared over the horizon.

3. Gravity measurements

More on Gravitational Measurements

Gravity is the force of attraction between any two objects.

The Law of Gravitation – the gravitational force is proportional to the square of the distance between the two centers of attracted objects.

• If Earth was a perfect sphere, then the force of gravity would be the same anywhere on the surface. But, the force of gravity is actually greater at the poles than at the equator. Thus, the distance from the poles to the center of the Earth is less than the distance from the equator to the center of the Earth!

More on Gravitational Measurements

Altitude of Polaris (North Star)

The altitude (height or angle made between the observer’s eye and the observer’s horizon) of Polaris is equal to the observer’s latitude (only in the northern hemisphere).

ALTITUDE OF POLARIS = LATITUDE (IN NORTHERN HEMISPHERE)

How smooth is Earth?

Earth’s Highest point is Mt. Everest (8.8km).

Earth has an average diameter of 12,735km.

Therefore Earth is actually a very smooth planet.

Some Good Models of Earth…