Arrived home 10:30pm July 29 2013, exiting car in driveway, clear dark country skies, noticed the huge (football field size) triangle over-flying residence, north-bound. Steady speed 30mph, straight track. Constant altitude about 1500-feet. Hollered to husband to come outside, did not think of camera.Quiet country location, carefully listened - zero sound emitted. Red flashing lights each corner (3), each seemed the size of car headlight - instant-on/off flashing. No center light/structure.As triangle gained distance, the "far" red light disappeared, apparently obstructed by triangle body. Triangle continued steady-speed northbound until out of sight, several minutes clear viewing time. Perfect triangle shape and size remained exact.Did not notice if "transparent" or obscuring stars - did not pass in front of any significantly bright stars to attract attention to this. Feeling is - solid definite craft structure.Latitude: +46.1835Longitude: -117.2694