Polar radius vs equatorial radius
The earth is an oblate ellipsoid or spheroid with some bulging
at the equator and a flattening at the poles.
Based on reference
ellipsoid accepted by geodesists and geophysicists in 1980, the earth has an equatorial
radius of 6378.136km and a polar radius
of 6356.751km.
But judging from a
radius of an equivalent sphere r which is 6371.00km, compared to best fitting sphere
the spheroid is flattened by about 14.2km at each pole and the equator bulges by about 7.1km.
The polar flattening is
defined as the ratio of f=a-c/c,
Where a is equatorial radius and c is polar radius.
The cause of the polar
of the polar flattening is deforming effect of the centrifugal acceleration.
This maximum at the equator where the
gravitational acceleration is smallest.
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