  The atmospheric activity of the Sun and Sun-like stars is analyzed involving
observations from HK-project at the Mount Wilson Observatory, the California
and Carnegie Planet Search Program at the Keck and Lick Observatories and the
Magellan Planet Search Program at the Las Campanas Observatory. We show that
for stars of F, G and K spectral classes, the cyclic activity, similar to the
11-yr solar cycles, is different: it becomes more prominent in K-stars.
Comparative study of Sun-like stars with different levels of the chromospheric
and coronal activity confirms that the Sun belongs to stars with the low level
of the chromospheric activity and stands apart among these stars by the minimum
level of its coronal radiation and the minimum level of its variations of the
photospheric flux.
