1. Shape of the Earth: The Earth is not a true sphere. Its shape is that of an oblate spheroid, the equatorial diameter being more than polar diameter. The equatorial diameter is 7926.7 statue miles while the polar diameter is 7899.5 km statute miles. In kilometers the equatorial radius is 6378.16 and the polar radius is 6356.77 km. The difference of about 27 miles between these diameters as compared to the average diameter of 7913 miles is so small that the Earth may be considered a true sphere for most purposes.
2. AXIS: The axis of the Earth is the diameter about which it rotates.
3. Poles: The geographical poles of the Earth are the two points where the axis meets the Earth’s surface.
The Earth rotates about its axis once a day. This rotation carries each point on the Earth’s surface towards East. West is the direction 180° from East, North is the direction 90° to the left of East, and South the direction 90° to the right of East. The two poles of the Earth are designated North Pole and South Pole, accordingly.
4. A Great Circle: is a circle on the surface of a sphere, the plane of which passes through the centre of the sphere.
There is only one great circle through any two points on the sphere’s surface, except if the points are at the two ends of a diameter when an infinite number of great circles are possible.
5. A small circle: is a circle on the surface of a sphere, the plane of which does not pass through the centre of the sphere.
6. Equator: The Equator is a great circle on the surface of the Earth, the plane of which is perpendicular to the Earth’s axis. The Equator divides the Earth into the north and the south hemispheres. Latitudes are measured North or Equator.
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