From left to right: empirical distribution of the RMS, amplitude range, and F8 measurements evaluated on a set of one-day VIRGO subseries taken during a solar-cycle minimum (2008, colors are related to the three SPM channels). The empirical distributions obtained during a solar-cycle maximum (2003) are shown by the black contours. Distributions derived using the HMI data described in Sect. 3 are shown by the yellow histograms.In each panel, the vertical dashed line indicates the transit depth expected for an Earth analogue (84 ppm).