The Rotation of Sun and Stars

The Sun and stars rotate in different ways and at different velocity rates. The knowledge of how they rotate is important in understanding the formation and evolution of stars and their structure. The closest star to our Earth, the Sun, is a good laboratory to study in detail the rotation of a G star and allows to test new ideas and develop new techniques to study stellar rotation. More or less massive, more or lessevolved objects, however, can have averydifferent rotation rate, structure and history. In recent years our understanding of the rotation of the Sun has greatly improved. The Sun has a well-known large-scale rotation, which can be m- sured thanks to visible features across the solar disk, such as sunspots, or via spectroscopy. In addition, several studies cast light on differential rotation in the convective zone and on meridional circulation in the radiative zone of the Sun. Even the rotation of the core of the Sun can now be studied thanks to various methods, such as dynamics of the gravitational moments and of course, helioseismology, through g-modes analysis. Moreover, the magnetic field is strongly linked to the matter motions in the solar plasma. The solar magnetic field can be measured only at the surface or in theupperlayers.Itistheproductof theinternaldynamoorof thelocaldynamos if they exist – in any case magnetic field and rotation cannot thus be separated.