I finished writing a book entitled Solar Magnetohydrodynamics back in 1981, which grew out of a postgraduate lecture course at St Andrews. Since then, the whole field has been completely transformed by spectacular new observations from spacecraft and ground-based telescopes which have spawned entirely new theoretical concepts. Rather than tinker with that book, I have therefore completely rewritten it from scratch and have given it a new title, Magnetohydrodynamics of the Sun.

Magnetohydrodynamics (or MHD for short) is the study of the interaction between a plasma (or electrically conducting fluid) and a magnetic field. A magnetic field affects a plasma in several ways. It exerts a force which is able, for instance, to support material in a prominence against gravity or propel it away from the Sun at high speeds. It provides thermal insulation, and so allows cool plasma to exist alongside hotter material, as in prominences or spicules. It also stores energy, which may be released violently as a solar flare or sporadically to heat the corona.

Solar MHD has now blossomed to become a central part of solar physics, since the key role of the magnetic field in producing many dynamic processes on the Sun has been recognised, and in turn solar physics has become one of the most vibrant parts of astronomy. The Sun influences the Earth's climate and space weather and plays a crucial role as a key for unlocking the secrets of many cosmical plasma phenomena.