Earth+dimensions+and+measurement

=Earth’s Shape and Dimensions – Key Ideas=
 * __Earth is Spherical__** – The Earth is not flat or round, but it is an **//__oblate spheroid__//**. This means that the Earth is //slightly// flattened at the poles, and it bulges //slightly// at the equator (Earth’s equatorial circumference is greater than its polar circumference). This is caused by Earth’s rotation (spin).

Early evidence that Earth is spherical:

 * The mast of a ship is the first part to appear over the horizon when approaching port.
 * Ships sailing north would see Polaris (north star) rise in the sky, and get lower as they sailed south. Polaris is not visible in the southern hemisphere.
 * **The angle of Polaris above the horizon is your line of latitude!!**
 * **During a lunar eclipse the edge of Earth’s shadow appears as an arc of a circle on the moon’s surface.**

The force of gravity pulling down on us (toward the center of the Earth) causes us to have weight. The farther we are from the center of the Earth, the less we weigh. Therefore, we actually weigh **more** at the poles since we are slightly closer to Earth’s center. We weigh slightly **less** at the equator!

=Measuring Earth’s Circumference -=


 * //__Eratosthenes’ Method__// __(formula)__**

__Example:__


 * __Earth’s Density__** – The density of an object is defined as the amount of material (mass) in a given amount of space (volume). As you go deeper in the Earth, the mass of the rocks above press down on the rocks below, decreasing their volume. This causes the rocks to increase in density (Reference Tables).

Formula (Ref.Tables): Density = Mass / Volume (g/ml __or__ g/cm³)
Cutting an object into pieces, no matter how many, __does not__ change its density! This is true, because you are not changing what the object is made of.