Introduction

It is now time to summarize and conclude but, regrettably, it is not possible to follow the King's advice, for the end of this story is not yet in sight. As in any good detective story, both clues and red herrings have been scattered liberally throughout the foregoing chapters. Unlike the novelist, however, we cannot be certain which is which and so cannot now discard the red herrings, marshal the significant clues, and reveal the solution. At best, we can indicate what appear to be the important themes which must form part of the solution and suggest the crucial areas of investigation which may lead to a satisfactory resolution.

Two important questions currently remain without clear and unequivocal answers:

1. (i) Do both cyclic and non-cyclic stellar activity arise as a result of dynamo action and, if so, of what kind (or kinds)?

2. (ii) Is the aperiodicity of solar cyclic activity evidence of a chaotic system, and, if so, can the existence of a strange attractor be demonstrated and its dimension determined?

Until firm answers can be provided for these questions, the problem of cyclic stellar activity remains without a satisfactory solution.

The input from stellar cycles

Because of the more extensive data-base regarding the solar cycle, the discussions in this volume are weighted heavily in that direction, but this in no way implies a greater importance to solar over stellar studies. Although still in their infancy, studies of stellar activity have already made a significant contribution to our understanding of the problem of cyclic activity.