  The first observations of Saturn's visible-wavelength aurora were made by the
Cassini camera. The aurora was observed between 2006 and 2013 in the northern
and southern hemispheres. The color of the aurora changes from pink at a few
hundred km above the horizon to purple at 1000-1500 km above the horizon. The
spectrum observed in 9 filters spanning wavelengths from 250 nm to 1000 nm has
a prominent H-alpha line and roughly agrees with laboratory simulated auroras.
Auroras in both hemispheres vary dramatically with longitude. Auroras form
bright arcs between 70 and 80 degree latitude north and between 65 and 80
degree latitude south, which sometimes spiral around the pole, and sometimes
form double arcs. A large 10,000-km-scale longitudinal brightness structure
persists for more than 100 hours. This structure rotates approximately together
with Saturn. On top of the large steady structure, the auroras brighten
suddenly on the timescales of a few minutes. These brightenings repeat with a
period of about 1 hour. Smaller, 1000-km-scale structures may move faster or
lag behind Saturn's rotation on timescales of tens of minutes. The persistence
of nearly-corotating large bright longitudinal structure in the auroral oval
seen in two movies spanning 8 and 11 rotations gives an estimate on the period
of 10.65 $\pm$0.15 h for 2009 in the northern oval and 10.8$\pm$ 0.1 h for 2012
in the southern oval. The 2009 north aurora period is close to the north branch
of Saturn Kilometric Radiation (SKR) detected at that time.
