Clear sighting of UFO

I was looking out the window of a moving trailer. I then suddenly saw a saucer with little square windows all the way around lit up with light. The saucer was flying fairly slow and low to where it was clear of view. The saucer span in circles while moving forward. For example, like if somebody is holding a spinning basketball on their fingure, and walking forward while the ball is spinning. The saucer flew out of my view.