Solar magnetic fields: Models and observations

The activity in the atmosphere of the Sun is largely determined by the ubiq uitous magnetic fields. Their modeling and observation is, however, hindere d by mathematical and experimental difficulties. These are reviewed briefly , and some applications and results are shown on the example of a solar act ive region (NOAA 3804, July, 1982). To resolve the problem of the ambiguity of the measurement of the direction of the transversal magnetic field a me thod developed by E. Teller and collaborators more than 40 years ago gives the physically most plausible results.