  The generation of magnetic flux in the solar interior and its transport to
the outer solar atmosphere will be in the focus of solar physics research for
the next decades. One key-ingredient is the process of magnetic flux emergence
into the solar photosphere, and the reorganization to form the magnetic
phenomena of active regions like sunspots and pores.
  On July 4, 2009, we observed a region of emerging magnetic flux, in which a
proto-spot without penumbra forms a penumbra within some 4.5 hours. This
process is documented by multi-wavelength observations at the German VTT: (a)
imaging, (b) data with high resolution and temporal cadence acquired in Fe I
617.3 nm with the 2D imaging spectropolarimter GFPI, and (c) scans with the
slit based spectropolarimeter TIP in Fe I 1089.6 nm. MDI contiuum maps and
magnetograms are used to follow the formation of the proto-spot, and the
subsequent evolution of the entire active region.
  During the formation of the penumbra, the area and the magnetic flux of the
spot increases. The additional magnetic flux is supplied by the adjacent region
of emerging magnetic flux: As emerging bipole separate, the poles of the spot
polarity migrate towards the spot, and finally merge with it. As more and more
flux is accumulated, a penumbra forms. From inversions we infer maps for the
magnetic field and the Doppler velocity (being constant along the
line-of-sight). We calculate the magnetic flux of the forming spot and of the
bipole footpoints that merge with the proto-spot. We witness the onset of the
Evershed flow and the associated enhance of the field inclination as individual
penumbral filaments form. Prior to the formation of individual penumbral
sectors we detect the existence of 'counter' Evershed flows. These in-flows
turn into the classical radial Evershed outflows as stable penumbra segments
form.
