Ted Sung wrote:
When talking about the rotation of spiral galaxies, it almost always
seems to mean rotating in a plane. I was wondering if it was possible
that the galaxy also precesses much like a spinning top. Perhaps this
would occur when the galaxy was young. Has this ever been observed?
Could it?

A galaxy disk could show precession under the influence of some
external torque whidch is misaligned with its rotation, but not
all radii in the disk would respond at the same rate. Some
spirals in interacting systems do show such disk warps with
radius (especially if we happen to see this warp from the
clearest direction or can see how foreground dust doesn't match
the plane of stars behind it), as in Arp 230 from the HST
public-release pictures. Such warps can be long-lasting once
excited - which is why evidence of warps in the outer disk of the
Milky Way and Andromeda are discussed in terms of past encounters
or minor mergers.

Bill Keel