The planets approximately orbit the sun, but a more precise statement is that the planets and the sun all orbit around a common barycenter.
Because the sun is so massive, this barycenter is very close to the sun. If we take the sun to be the origin, the barycenter travels in a complex, nonlinear trajectory (from Wikipedia):
Modeling this accurately is critically important to predicting celestial events. I wrote a simulator to predict the 2012 transit of Venus, based on estimates of orbits and the assumption that the sun is at the origin.
The error introduced by these assumptions was enough to miss the transit by a solar diameter.
This data must exist, since the transit actually did happen. Additionally, errors in the orbital data of the planets could have affected it. Where can I find data on where the planets and the sun are and what trajectories they're moving in (relative to the solar system's barycenter)?