Hello Ward,

On Friday March 21 2008 09:49, you wrote to me:

 Mv>> You'r right of course. Its course as seen from the ground varies
 Mv>> from SW->NE to NW->SE. Apromimately.

 Mv>> That does not stop anyone from speculating what would happen
 Mv>> /if/...

 WD> I wonder: Earth is not a perfect sphere ...

Indeed. First approximation: sphere.
Second approximation: ellipsoid flattened at the poles.
Third approximation: Pear shaped
Fourth approximation: ...

 WD> is the orbit of the ISS then a perfect circle, an elips or something
 WD> wobbly?

Even with the earth a perfect sphere the orbit is more likely elliptical
than circular. As the orbit is not in the equatorial plane, the equatorial
bulge will exert a force in the direction of the equatorial plane that
causes precession of the orbital plane. I.e. the orbit "wobbles".

Deviations from the perfect orbit are also caused by the moon, the sun and
other planets. In decreasing order of the magnitude of the effect.


Cheers, Michiel

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