Observed longitudinal sunspot distribution (left) and longitudinal spot distribution obtained from the analysis of the VIRGO/SPM solar time series for the spots-and-faculae model (middle) and the spots-only model (right) during cycles 23 and 24. The longitudinal map is extended at each edge to reflect the periodic nature of the distributions. In all three panels, the grey hatched areas highlight the time interval for which VIRGO/SPM observations are lacking.