silent isosceles triangle shaped mirage-like UFO with no lightsAs far as the exact date and time go, I cannot be certain. It was definitely in the fall of 1987. I was a junior in high school at that time and on one particular evening my astronomy class went to the observatory on the Yankton College campus. That campus is now a federal prison. That evening was very clear and I don't think there was much of a moon. Our assignment was to look through the telescope and then write down on our sheet how many rings we could see around Saturn, moons around Jupiter, etc. When I had finished my assignment I went back outside and stood with the other students on the hill on which the YC observatory is located. There were maybe 10-12 of us there all talking about whatever when several of us just became suddenly quiet as an isosceles triangle shaped object in the sky to the west moved through our line of sight south to north. It had no lights and made no sound. Its only discernable feature was that it seemed to distort the sky behind it and the light of the stars it passed in front of in relation to us; kind of like heat waves rising off the pavement. There were no additional colors. Even though I can't describe the actual aircraft the shape of the visible distortion was definitely an isosceles triangle moving in the direction of the angle made by the two equal sides. The base, or the back of the object in relation to its direction of movement, was a little longer than the two equal sides. The translucent nature of the object makes it difficult to determine speed, size, or distance with accuracy. The YC campus(Yankton Federal Prison) is not very big and is in a residential area. From where we were standing on the hill the object didn't seem to be more than a few blocks away at an altitude of 200 feet, possibly lower. At arms length it was aproximately 5-6 inches from top to bottom and 3.5 to 4 inches from front to back. I did not get the impression that this was an extremely large aircraft. When I caught site of the object I was facing southwest, and it moved! straigh t north until it was out of sight in five or six seconds. Since it was night time and the object had no lights this probably wasn't a great distance, so it was most likely not moving incredibly fast. Yankton is a smaller town so there aren't as many street lights as there are in bigger areas. If this was not the case the object may have gone completely unseen. Myself and possibly six or seven other people witnessed this event. At this time I can only remember one or two who could corroborate this story.Even though this happened fifteen years ago those five or six seconds are burned into my memory like a movie clip that I can replay. I've never seen anything like it since.((NUFORC Note: Date is approximate. PD))