We were driving and saw motion in the sky then dissappeared.We just finished driving a friend home after a movie. Me, the driver spotted a small object high in the sky. At first we all thought it was a plane but since my father is an avid aviator I knew that it wasn't anything like the sort. It was heading left in our field of vision then, raised and fell. Since we were going down a hill it left bwehind some trees, but when we crested the next hill to investigate it was gone. There was NO chance of it still being behind the trees for this hill was very high and had a good overlook of the city. The craft was hard to determine its's actual shape for the sky was dark but clear. Anyway the way the lights were flahing it looked circular in shape. All passengers in the car are high school students.