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6.2 Form of the Earth
6.2.2 Describe the general shape of the earth.
- Strictly speaking, the Earth is not a sphere, but a spheroid.
- Which means it is slightly flattened at the poles.
- And because the Earth rotates around its North and South pole axis, it is called an Oblate Spheroid.
- But in practice the earth is regarded as a perfect sphere.
6.2.4 Define and identify, on a diagram of the earth:
(a) Axis and Direction of Rotation;
- The poles of the Earth are the extremities of the Earth's axis of rotation, and are fixed locations which the earth rotates about.
- They are referred to as the North and South Geographic Poles, also known respectively as True North and True South
- The direction of the Earth's rotation is from West to East, or, to an observer looking down on the North Pole, it is turning anti-clockwise.
(b) Geographic and Magnetic Poles;
- The magnetic pole is a point where the Earth's magnetic field goes vertically down into the planet.
- The geographic and magnetic poles are not situated in the same place.
- The north magnetic pole is currently about 400km south of the north geographic pole, but can move to about 1,000km away.
- The earth is essentially a large magnet with a field of magnetic force, or flux, around it.
- A freely suspended compass needle will align itself with the flux lines and under most conditions a stable direction reference is provided with reference to the magnetic poles.
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