Thursday, November 01, 2018

[zswcvjin] Pear or egg shaped earth

To first approximation, the Earth is a sphere.  To second approximation, the Earth is an oblate ellipsoid.  What is its shape to third approximation?  Is it still a surface of revolution?

EGM96 describes the shape of the Earth with spherical harmonics.  What is the base shape: sphere or ellipsoid?  If a sphere, does using just the first harmonic turn it into an oblate ellipsoid?  I'm guessing not.

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