what is galactic motion
and how can you explain it?
What do you mean by galactic motion? The fact that the all galaxies are moving away from each other or something else?
Galaxies that are in motion
The galactic motion (aka movement of galaxies) can be explained by forces and the inflation of space-time.
the inflation of space-time is one part
there is also proper galactic motion , motion thru space
ie movement toward the great attractor
or our galixcy moving toward big A
not every galixcy is moving apart
There is the motion of galaxies THROUGH space. This is no different than a comet zipping through space, except in scale. For instance, Andromeda is coming at us like a freight train (should be here before Sol goes red giant).
Than there is the motion of galaxies IN space. Like everything else, galaxies are imbedded in the fabric of the universe. That fabric is expanding, carrying galaxies (and everything else) along with it.
Note that objects moving THROUGH space can not exceed the speed of light, while no such speed limit exists for the FABRIC of space. Galaxies can not move faster than light, but they can be carried away faster than light by the expansion of the fabric of space.
I think you may find the following web site useful to you anaguma:
Separate names with a comma.