I will show that there is an asymmetry in the main-sequence star counts on either side of the Galactic plane, as one looks towards the Galactic anticenter. This can be explained if the disk of the Milky Way oscillates up and down. This oscillation could provide an explanation for the Monoceros Ring and, also, for the TriAndromeda Stream (or Ring). The implication is that the stellar disk extends out to at least 25 kpc from the Galactic center – much farther than the canonical 15 kpc that is typically quoted. The oscillations are aligned with the spiral arms of the Milky Way and are plausibly consistent with previous predictions for disk ringing due to a Sagittarius-dwarf-sized galaxy plunging through the disk.