Zodiacal Light as seen from near the summit of Kitt Peak, 
Arizona in April of 1977. This
appears as a "false twilight" and is shaped like a wide band arcing above
the horizon unlike true twilight that hugs much more of the horizon.
This is visible just after "official" twilight ends and is distinct from the
Milky Way. It is caused by sunlight scattering off of dust particles in
orbit around the sun.