These subjects have been the focus of several topical symposia, so
in
order to narrow the subject I will concentrate on stars like the Sun and
primarily on rotation. I will discuss observations and models
that treat the rotational history of the Sun and stars like it, and show
how observations of activity in these stars help as well.
First I provide some context for rotation in solar-type stars, both compared to other stars and in historical terms. Observations of solar-type stars in young clusters almost 20 years ago revolutionized our view of the evolution of angular momentum by showing how different and unpredictable stars could be. The study of clusters has been vital in this area because they not only provide samples of stars of know age, but large samples as well, so that statistical properties can be understood. Also, the most interesting stars for this work are very young, meaning clusters are almost the only places where they are found anyway. Observing stars in clusters means working on faint objects, and the new generation of large telescopes with outstanding instruments, such as Keck + HiRes, has been crucial.
By these means observers have kept one step ahead of the modelers because the many parameters that must necessarily go into the models leave them poorly constrained. Nevertheless, important conclusions about angular momentum loss and the mechanisms that drive it can be drawn. This field continues to provide fascinating surprises as we explore new clusters.
Just as important have been new generations of space instrumentation, especially Rosat. Young stars are bright in x-rays, making it easy to find and study the members of young clusters that would otherwise be difficult to distinguish from the field. This benefit, however, leaves a potentially significant bias present in some samples.