Helioseismology provides us with means to investigate the otherwise invisible solar interior. The seismic approach is indispensable for the study of internal structure and evolution of the sun. It is even more so, however, for the study of dynamical aspects of the sun, because of the lack of other reliable means. The current status of seismology of solar rotation is reviewed and outstanding problems are discussed.

Introduction

In 1984, Douglas Gough started his paper, entitled ‘On the rotation of the Sun’, by pointing out our lack of understanding of the dynamical history of the sun (Gough 1984). The question of how the sun has evolved dynamically, since its arrival on the main sequence, still stands as one of the big questions in astronomy. With an increased level of interest attracted by the issue of how our solar system (and other ‘solar’ systems) formed and evolved, it may be a problem of even greater importance today.

Another big problem regarding the solar rotation is what is behind the solar cycle, and if a dynamo mechanism is responsible, as is generally believed, how it works. Here, too, the problem seems to be recognized in a wider community because of the great interest currently shown towards the solar-terrestrial study.

In tackling both problems, an important key is the dynamical structure of the sun today, and in particular how it rotates. Observational clues are not many.