Re: Vanguard and the shape of the Earth - was Articles of generalinterest

Jim Varney (
Sun, 8 Mar 1998 22:07:26 -0800

Ted Molczan wrote:

>This situation is approximately reversed in the Southern
>Hemisphere. So when drawn with these deviations exaggerated,
>to make them obvious, the pear shape is a reasonable

Nit-picking time: the "pear-shaped geoid" technically has no relationship to
the overall shape of the Earth's surface.

The geoid is an equipotential surface.  Any place on the geoid feels the
same force of gravity as any other place on the geoid.  Mass concentrations
in the Earth will cause the geoid to rise relative to the surface;
conversely, low density regions make it fall.  The Earth could be square and
the satellite wouldn't know or care; all it knows and cares about is the
distribution of mass (and therefore gravity) in the body it is orbiting.
Jim Varney     121.398 W, 38.458 N, 8m     Sacramento, Calif.
Member, Sacramento Valley Astronomical Society