  We report on new observations of the motion of zodiacal dust using optical
absorption line spectroscopy of zodiacal light. We have measured the change in
the profile shape of the scattered solar Mg I 5184 line toward several lines of
sight in the ecliptic plane as well as the ecliptic pole. The variation in line
centroid and line width as a function of helio-ecliptic longitude show a clear
prograde signature and suggest that significant fraction of the dust follows
non-circular orbits that are not confined to the ecliptic plane. When combined
with dynamical models, the data suggest that the zodiacal dust is largely
cometary, rather than asteroidal, in origin.
