Comprises an up-to-date description of the astrophysical characteristics of the sun, including modern techniques used in solar research. Provides an historical background of solar research and techniques and covers the necessary astrophysics for solar studies, energy generation in the interior, the convection zone, the non-thermally heated layers. Solar wind are described in detail. Also considers the sun in relation to other stars, including information on its variable outputs of light, charged particles and fields. Features extensive references and numerous problems.