Stellar magnetic activity: lessons for, and from, the Sun

The Sun, as the nearest cool star, has shaped our thinking about magnetic activity of other stars that share the critical properties needed to drive a dynamo: a convective envelope directly underneath the surface, with stellar rotation setting the intensity of the activity. Spots, faculae, chromospheres, coronae, and flares are shared concepts common to the solar and astrophysical communities. But how far does the solar paradigm reach as we look at increasingly more active stars or, equivalently, at an ever younger Sun? Active stars may exhibit spots far larger than those observed on the Sun, often at polar latitudes where no solar spot has ever been reported. Other cool-star phenomena that have no obvious solar counterpart are persistently active longitudes and superflares that are far more energetic than solar events directly observed in the space age. Even activity cycles seem not to be a particularly common feature in stars. In this talk, I will compare the Sun to its peers, exploring where the paradigm holds and where it may fail. I will also look at this in the context of applications such as space weather and exoplanet transit analysis.