Example of a planet-only fit (dashed orange line) to the planet–moon model (solid black line). The star is sun-like, the planet is Jupiter-sized and in a 30 d orbit around the star, and the moon is Neptune-sized and in a 3.55 d orbit around the planet. In this example, the fitted planet-to-star radius ratio (r_fit), which goes into the calculation of the transit depth with a power of two, is slightly overestimated due to the photometric signature of the moon. As a comparison between the amplitude of the moon signal and the expected noise, the noise from the Poisson statistics of an m_V = 8 star (using a 1 h binning) is 12.6 ppm for PLATO and 6.0 ppm for Kepler. This is two magnitudes smaller than the amplitude of the moon signature but possibly comparable to the effect of stellar noise, from activity for example.