evidence: We know from magnetic records locked in rocks that the Earth's magnetic field has reversed many times in the past. We don't really know why but we have some theories that are being borne out in mathematical models. We also know that the magnetic field of the sun reverses as well-- every 11 years, whereas the Earth's reverses irregularly. The last geomagnetic reversal for Earth was about 780,000 years ago. The historic reversal rate for Earth seems to be once every few hundred thousand years, but it has varied widely; on at least two occasions, the field has maintained one polarity for tens of millions of years. [...] The simulation yielded relatively long periods, when the field was roughly aligned with the rotation axis, that were separated by a rapid flipping of the poles. During this simulated reversal, the non-dipole field became dominant. Attempts are now underway to determine the morphology of the transitional fields during reversals. And it is hoped that these results will inspire still more realistic models and a better understanding of the working of the geodynamo.