Abstract:
The role of the Ca II K line as a reliable diagnostic of the chromospheric activity on the Sun is reviewed. The chromospheric structures seen in this line serve as good indicators of the photospheric magnetic structures and also mimic the morphological changes in the surface magnetic features associated with the solar cycle. Similar changes can be expected to take place in other sun-like stars and could therefore be used as a diagnostic for inferring the kind of structures of surface magnetic fields in them.
