  An oscillating vertical displacement of the Milky Way, with a wavelength of
about 8 kpc and and amplitude of about 100 pc (increasing with distance from
the Galactic center) is observed towards the Galactic anticenter. These
oscillations are thought to be the result of disk perturbations from dwarf
satellites of the Milky Way. They explain the Monoceros Ring and could be
related to Milky Way spiral structure.
