Shape of the Earth
The earth is not true sphere.It's shape os that of an oblate spheroid,the equatorial diameter being more than the polar diameter.
AXIS
The geograph poles of the earth are two points where the axis meets the earth surface.
The earth rotates about it's axis once each day.This rotation carries each point on the earth surface towards East West in the direction 180 degrees from East,North is the direction 90 degrees to the left of the East & South the direction 90 degrees to the right of the East.The two poles of the earth designed North pole & South pole accordingly.
GREAT CIRCLE
Great circle is a circle on the surface of the sphere,the plane which passes through the center of the sphere.
There is only one great circle through any two points on the sphere's surface,except if the points are two ends of the diameter when infinite number of great circles are possible.
A great circle is the longest line that can be drown around the earth,A segment of the earth great circle is the shortest distance between two points on the earth surface.
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