Moving lights in Minnesota sky disappearing into what appeared to be a trail of smoke.

The first thing we noticed was a weird trail of smoke almost appearing as though a rocket had been shot off or crashed.  We went to follow the smoke first, but then saw these weird lights that almost looked like moving stars.  They were very synced in their movements.  One would fly off into this trail of smoke (still in the sky for over 30 minutes) then it would disappear.  The next would follow, and so on.  As they enter this what appeared to be a trail of smoke they would disappear.  The trail of smoke would then shift and became larger in the sky.  We watched this happen for 2 hours consecutively.