That's possible. It's also possible that it does not rotate in the Milky Way at all. Earth would still be passing through it faster for the part of the year whe

That's possible. It's also possible that it does not rotate in the Milky Way at all. Earth would still be passing through it faster for the part of the year where our rotation around the sun has us going at a faster velocity around the center of the galaxy. If it helps, think of your car's tire as you drive down the road at speed v. The part of the tire that touches the road at any instant has no speed (relative to the road), and the opposite point on the tire is travelling at 2*v (still relative to the road).