That is dependent upon a lot of factors. The Earth's axial tilt wobbles between 21 and 25 (approximation) degrees. Many scientists believe these wobbles (Milankovitch Cycles) are what help to create the Earth's periods of glaciation and warming. Basically, these wobbles are caused by the system's primary and all other planet's in the stellar system playing constant tug-of-wars on the Earth.
Of course, if you believe in the Nemesis Hypothesis (a coalstar with tremendous gravity well is in an elliptical orbit around our sun that cycles every 65,000,000 years (or so)), then Nuelan's Nemesis could be passing close and thus throws Nuelan's axis off. Of course, there is the perterbations of any comet and asteroid orbits that can cause a shooting gallery...
Also, there is the magnetic field polarity reversal that can cause all kinds of havoc. It has even been proven here on Earth. In the studies done on the mid-oceanic ridge in the Atlantic, they have found that as the ridge feeds new ocean floor, that it has created stripes of magnetic reversal. I'll look for some links about this and post them.
rmfr