The figure of the Earth is not exactly spherical; it approximates to a very slightly oblate spheroid, the ellipticity (c−a)/a being only 0.00335. (The actual figure of the Earth, mean sea le...The figure of the Earth is not exactly spherical; it approximates to a very slightly oblate spheroid, the ellipticity (c−a)/a being only 0.00335. (The actual figure of the Earth, mean sea level, is often referred to as the geoid.) Let us refer the ellipsoid ??? to a set of axes Ox′y′z′ such that the angles z′Oz and x′Ox are each θ, and the y^\prime- and y-axes are identical.
The distribution of mass around the minor axis is the same as for a circular lamina of radius a, and therefore the moment B is the same as for the circular lamina, namely \( B = \frac{1}{4}...The distribution of mass around the minor axis is the same as for a circular lamina of radius a, and therefore the moment B is the same as for the circular lamina, namely B = \frac{1}{4} ma^2 . The moments of inertia of an elliptical ring of mass m and semi major and semi minor axes a and b are c_1ma^2 about the minor axis and c_2ma^2 about the major axis, where c_1 and c_2 are shown as functions of b/a .
