  Penumbrae are known to be area of mainly horizontal magnetic field
surrounding umbrae of relatively large and mature sunspots. In this paper, we
observationally studied the formation of penumbrae in NOAA10978, where several
penumbral formations were observed in G-band images of SOT/Hinode. Thanks to
the continuous observation by Hinode, we could morphologically follow the
evolution of sunspots and found that there are several paths to the penumbral
formation: (1) Active accumulation of magnetic flux, (2) Rapid emergence of
magnetic field, and (3) Appearance of twisted or rotating magnetic tubes. In
all of these cases, magnetic fields are expected to sustain high inclination at
the edges of flux tube concentration longer than the characteristic growth time
of downward magnetic pumping.
