Recall that geostationary satellites are placed into an orbit which is designed to stay above a fixed point on the Earth's surface. If the Earth and the satellite were both spherical cows in an otherwise-empty universe, the satellite, once placed in orbit at geostationary altitude over the equator, would presumably co-rotate with the Earth for the rest of time.
But, of course, there are no spherical cows. Real satellite orbits are presumably perturbed by various factors, like gravity from other large bodies (especially the moon?); collisions with "stuff" (dust, etc.); and the non-constant motion of the Earth itself (tidal deceleration, earthquakes altering the Earth's mass distribution, etc.).
This brings me to my two questions:
- How much does a typical geostationary satellite wobble away from its designated position over the Earth before being station-kept back into place?
- Which factors contribute the most to this wobble?