Model light curve of star with 30-day rotation period covered by spots and observed from its equatorial plane. The spots decay according to a linear law with T_spot =25 d. Two upper panels: normalized light curve (panel a) and corresponding Lomb–Scargle periodogram (panel b). Panels c–f: global wavelet power spectra (left panels) and corresponding gradient of the power spectra (right panels) calculated with the 6th order Morlet wavelet (panels c and d) and with the sixth-order Paul wavelet (panels e and f). The values of the gradients of these power spectra are a scaled and offset by unity (see Eq. (3) and the discussion in the text for the exact quantity plotted). Numbers in panels d and f correspond to the positions of the inflection points (i.e., local maxima of the gradient). Vertical dashed lines in panels b, c, and e indicate the rotation period of the modeled star. Vertical solid lines in panels d and f indicate the positions of the inflection points. We note that since spots reduce stellar brightness, the normalized variability (i.e., normalized F(λ, t) − F_Q(λ) values, see Eq. (1)) is plotted between −1 and 0.