  High-resolution observations of horizontal motions in the penumbra are needed
to complement the concept of penumbrae obtained from spectropolarimetry. Time
series of intensity images of a large sunspot in AR 10634 acquired with the
Swedish Solar Telescope in the G band and red continuum are analysed. The two
simultaneous time series last six hours and five minutes. Horizontal motions of
penumbral grains (PGs), structures in dark bodies of filaments, the outer
penumbral border, and G-band bright points are measured in time slices that
cover the whole width of the penumbra and the neighbouring granulation. The
spatial and temporal resolutions are 90 km and 20.1 s, respectively. In the
inner penumbra, PGs move toward the umbra (inwards) with a mean speed of -0.7
km s-1. The direction of motion changes from inwards to outwards at
approximately 60% of the penumbral width and the mean speed increases gradually
in the outer penumbra, approaching 0.5 km/s. This speed is also typical of an
expansion of the penumbra-granulation border during periods that typically last
one hour and are followed by a fast contraction. The majority of the G-band
bright points moves away from the sunspot, with a typical speed of 0.6 km/s.
High outward speeds, 3.6 km/s on average, are observed in dark bodies of
penumbral filaments. According to the model of penumbral filaments, it is
suggested that the speeds detected in the dark bodies of filaments are
associated with the Evershed flow and that the opposite directions of PG
motions in the inner and outer penumbrae may be explained by the interaction of
rising plasma in filament heads with a surrounding, differently inclined
magnetic field.
