Temporal evolution of the area covered by active region NOAA 11126 as it crossed the solar disk. The area enclosed by umbral cores and pores is displayed with a dashed line. Dashed dot dot line refers to the penumbra, whereas the solid line denotes the total area. Some smoothing was applied to the time-series to suppress features on temporal scales shorter than one hour. The vertical gray bars refer to the observing periods of HOP 0176 (2010 November 18 − 22). The labels indicate different stages of active region evolution, which are explained in Sect. 3.1.