ADVANCES IN SOLAR-STELLAR ASTROPHYSICS

The discovery on stars of coronae and of X-ray emission from flares in the 1970's opened up the investigation of stellar activity. Solar-ste llar astrophysics has now become a two-way street. The rich detail of the Sun provides a close-up view of physical phenomena, while the stel lar observations provide a way to, in effect, vary the otherwise fixed solar parameters. In this way we can study the evolution of the Sun, the dependence of activity on rotation, and the degree of autonomy bet ween magnetic fields and such fundamental parameters as mass and age. We present an overview of the Sun as a star, stellar coronae along the main sequence, the dividing line for evolved stars, rotation-activity relations, activity cycles, flux-flux relations, basal acoustic heati ng, evidence for coronal heating by microflaring, and a few facts abou t flares.