The Earth's equator, for instance, wobbles (or changes) in a predictable way -- the rotational axis moves; after 26,000 years, it returns to where it started. This is sometimes known as the "precession of the equator."
While Einstein's General Theory of Relativity includes gravity, his Special Theory does not. Gravity does not affect something as small as an atom, and the Thomas Precession, which describes atomic behavior, therefore falls under Einstein's Special Theory.
According to the Lorentz Transformation (developed by Dutch physicist Hendrik Lorentz in 1905, a few months before Einstein's Special Theory), two observers in different locations moving at different velocities will see the same events happening at different times and distances; this is because space-time must curve in order to accommodate the speed of light remaining a constant for both observers. The Lorentz Transformation therefore supersedes the old Newtonian physics of an absolute space and time. This idea became critical to Einstein's principle of relativity. The Lorentz Transformation does not apply to speeds far lower than the speed of light; there, Newtonian physics (which do not confound a human observer's common sense) still apply.
Say that you place two observers into an atom, one on the electron, one on the nucleus. The electron is moving at speeds far greater than the nucleus. Therefore one observer will be moving through time faster than the other observer. This is called time dilation. The rotational axis (the plain circumscribed by a rotating body) of the electron for the observer sitting on that electron will therefore look different than the electron's rotational axis does from the point of view of the observer stationed on the nucleus. This is the Thomas Precession, and it can be calculated mathematically from the point of view of either observer, to take into account the difference caused by the time dilation. The quantum-mechanical location of an electron cannot be determined accurately without it.