Was traveling south on Interstate between Billings and Hardin, Montana. Looked up toward the southeastern sky and saw was at first I thought was a plane, but it looked odd. The exhaust trail appeared to be going vertical and the trail was fanned out instead of line like you would see if watched a jet go across the sky. Then the exhaust trail dissipated, leaving a glowing starlike orb which moved across the sky to the south/southwest. I could not tell if it was changing directions or if was the turns in the road that I was driving on that made it appear like it was changing directions. It appeared to move effortlessly and became smaller and smaller as it got farther away. Even as it was in some light clouds I could faintly see it's glow, but eventually disappeared. I had a smart phone with a photo capabilities, but being on the interstate did not want to pull over for safety reasons and thought I could make it to Hardin and still get a photo, but was not able to get there by the time it was gone. I have spoken to other people who have also seen strange things in the sky in this area.