Triangular flying object with very dim lights seen flying northeast across the sky of west side of Billings, MT.I went outside for a cigarette around 7:25pm. I was gazing up, scanning the western sky when my eyes caught strange movement. It looked like a dark form that seemed to materialized nearly directly west of me, but I'll admit that it may have just seemed that it materialized when my eyes caught the movement. My eyes adjusted a bit and saw that the form was triangular, grey/almost translucent (hardly darker than the night sky behind it) and had three very dim lights with an almost pale greenish glow at the points of each of its triangular ends. It then flew (or continued to fly) northeast across the western sky out of view. It was flying at a lower altitude than an airplane, and I could not hear any sound although there was a bit of noise pollution from a nearby street. I don't know if I could accurately gauge its size, but I'd said it was not a large craft. A single point of the triangle seemed to be the nose of the craft, as that lead the direction it was flying. The lights/craft did not rotate, cease or hover once my eyes focused on it. I tracked it across the sky until I could no longer see it, it was moving quite fast, I'd say I watched it cross the western sky in about 5 seconds. I am a very practical person, down to earth and very skeptical about UFO sightings, but this was one experience that I can't explain.