Fifteen years ago, we modeled the distribution of stars in the Milky Way

using three components: an exponential disk, a power law spheroid, and a

bulge.  Then, we discovered the distribution of stars in the spheroid

was lumpy due to the accretion and tidal disruption of dwarf galaxies

that ventured too close the the Galactic center.  We now wonder whether

the Milky Way has a classical bulge at all; likely the bulge-like

feature we see is instead due to the Galactic bar.  And most recently,

we are discovering large scale departures from the standard exponential

disk.  New discoveries point to variations in the expected bulk

velocities of stars in the Galactic disk, and oscillations in the

spatial densities of disk stars.  Some believe these observations point

to a wave response to the passing of dwarf galaxies (or dark matter

lumps) through the Milky Way's disk.  These waves may also explain the

observed rings of stars, 15-25 kpc from the Galactic center, which is

farther out than we originally believed the disk to extend.

Refreshments will be served in CP 179 at 3:15 PM