Single-peaked light curve of comet ISON. Upper panel: rotational light curve of comet ISON phasing all the photometric data to the preferred period (14.4 h). Errors are not plotted for clarity, but each individual value has an uncertainty ~0.021 mag. A one-term Fourier fit (red curve) is shown on top of the data, the peak-to-peak amplitude derived from this fit is 0.03 ± 0.02 mag. The Julian date for zero phase angle is 2 456 332.47479 days. Lower panel: rotational light curve of comet ISON after applying a running median (0.05 step in phase) to the data showed in the upper panel. The rotational light curve variability is clearer to the eye in this plot. Like in the upper panel, a one-term Fourier fit (red curve) is shown on top of the data. Each individual point has an uncertainty ~0.015 mag.