10.13.1 Introduction

In the present document, the expression Solar-like variable is used to indicate a star whose variability can be ascribed to phenomena similar to those observed in the Sun. The Sun variability is mainly due to the evolution of its magnetic Active Regions (hereafter ARs), which are complexes of dark spots and bright faculae unevenly distributed over the stellar surface. The expression rotational modulation indicates the flux variations induced by the combined effects of the stellar rotation and the presence of ARs; stellar rotation modulates the ARs visibility and, as a consequence, the integrated optical flux coming from the star. Rotational modulation is a phenomenon widely observed in main-sequence stars with a spectral type later than F5 or in binary systems like RS Canum Venaticorum. The light curves of these stars are characterized by a flux modulation, whose periodicity corresponds to the stellar rotation period and whose amplitude is related to the area, distribution, and temperature of ARs. The analysis of these light curves, therefore, allows us to detect the stellar rotation period and to constrain the physical properties of magnetic ARs.