|MadSci Network: Astronomy|
There are a few things confused here; let me start by saying that there is no evidence that the Earth's geographical pole has ever reversed. Most of the planets rotate in the same direction - the exception is Venus where something odd must have happened at some point, but Earth goes along with the majority.
The Earth's magnetic poles do reverse every so often - we see evidence for this by looking at a record of the Earth's magnetic field preserved in the ocean floor. There is no way that this could have been caused by the influence of the Sun, or of the Milky Way, but it appears it is something to do with how the Earth generates its magnetic field.
Try the links in the MadSci Library for more information on Astronomy.