Lomb-Scargle periogram for three synthetic light curves from simulations with two spots at different latitudes, L₁ and L₂. Top panel: only one rotation period is detected. Middle panel: two peaks associated with the surface rotation are seen but the second is not within the detectable period range. Bottom panel: the rotation periods associated with each spot latitude are successfully detected. The spot latitudes are indicated in the left top left corner of each panel. The red symbols mark the first and second harmonics if detected. The yellow regions mark the detectability limit we impose (see text for details).