For , is an unstable stationary point and the interior minimum satisfies . Hence
The potential then diverges at . For , the turning point is specified exactly by the smaller quadratic root
For small positive , this approaches , a finite excursion even when the initial impulse is arbitrarily small. An excursion from the north pole to the outer turning angle and back has period
Near the unstable pole, with . The near-pole contribution gives , so the period diverges logarithmically as . The exactly unperturbed top can remain at the unstable vertical orientation; the limiting excursions spend ever longer close to it. The direction also precesses according to part c.